CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of priority of Singapore Patent Application No. 10202251283D, filed on 5 October 2022, the content of which being hereby incorporated by reference in its entirety for all purposes.

TECHNICAL FIELD

[0002] The present invention generally relates to a single-wing rotorcraft, a method of operating the single-wing rotorcraft and a method of forming the single-wing rotorcraft, and more particularly, a single-wing rotorcraft with multiple flight modes.

BACKGROUND

[0003] Unmanned Aerial Vehicles (UAVs) have been continuously gaining attention since their development, owing to the multitude of tasks they can accomplish involving mapping, inspection and observation. In the past, research has enhanced the performance and capabilities of traditional UAVs through additional flight modes. An additional flight mode can help to accomplish different objectives using a single platform. For example, there has been proposed a tri -tiltrotor UAV, which can perform a conversion between vertical take-off and landing flight mode and fixed-wing flight mode. As another example, there has also been disclosed a transformable hovering rotorcraft, which can achieve controllability in four degrees of freedom while in the horizontal cruising mode and five degrees of freedom while in the hovering mode. As a further example, there has also been introduced a flying robot that can roll over on the ground, through a gap that is narrower than its diameter.

[0004] Monocopters are single-wing rotorcrafts (which may also be referred to as singlewing rotating aerial vehicles), which achieve lift by spinning/rotating about the yaw axis. For example, inspiration for the monocopters may be taken from maple seeds (or samaras) which can utilize their shape to auto-rotate while falling. The monocopter platform has been used for various different practical applications, for example, in practical applications where its spinning nature can be utilized. For example, there has been disclosed an example of an unpowered monocopter-based lightweight sensor that can achieve soft landing due to its shape. Monocopters may also utilize a motor-driven propeller to achieve lift. For example, there has been disclosed a monocopter-based platform for short-range urban surveillance and sampling missions. There has also been developed three-dimensional electronic micro-fliers based on the monocopter platform, covering a wide variety of use case scenarios. The spinning nature of the monocopter platform may also be applied for passively scanning and mapping a surrounding environment using Simultaneous Localization and Mapping (SLAM). Similarly, there have also been disclosed applications for monocopters for simultaneous image and onboard state estimation and LiDAR inertial odometry, respectively.

[0005] On the other hand, a bicopter UAV may use two thrust units to generate collective lift force and torque in the roll axis using differential thrust. Additionally, two servos may be provided to produce torque in the pitch and yaw axes by tilting the thrust units. A number of studies have been conducted on the bicopter platform. For example, there has been developed a functional mini tiltrotor UAV, which (unlike the conventional tiltrotor swashplate mechanism) utilized the tilting of rotors to stabilize the UAV. There has also been presented a prototype based on research conducted on the principles of motion and the design of an attitude stabilizing controller based on a Proportional Integral Derivative (PID) controller. Besides these and various other studies, the concept of bicopters has been implemented on manned aircrafts as well.

[0006] For example, a comparison of main characteristics of example conventional monocopters and bicopters are presented in Table 1 below, which highlights a number of key differences between the two flight modes (monocopter and bicopter flight modes). For example, during hover, a monocopter spins its entire body while a bicopter has zero angular velocity.

Table 1 - Comparison of Conventional Monocopters and Bicopters

[0007] In a conventional monocopter, the aerodynamic force produced by the wing and the rotating motion provide its flight mode (monocopter mode) with passive stability while hovering. For example, the ability to auto-rotate helps the monocopter mode to reduce/minimize its impact when hitting the ground in case of power failure (i.e., a softer landing in case of power failure). Moreover, recent research has also demonstrated that the rotating wing platform has superior power/energy efficiency compared to other types of platforms. For example, monocopters may be employed for various practical applications where the spinning nature of the monocopter platform can be utilized, such as passively scanning and mapping a surrounding environment. However, even though the conventional monocopter platform is based on a single wing, the physical footprint of the spinning monocopter is large enough to hinder its mobility whereby the conventional monocopter platform has a highly nonlinear dynamic nature. Moreover, cost-effective sensors available in the market may struggle to measure the state of the conventional monocopter as they may not be able to keep up with the rotational speed of the conventional monocopter platform.

[0008] On the other hand, the flight mode (bicopter mode) of a conventional bicopter is steady with zero angular velocity during hovering, which helps to achieve position and attitude control with easier or simpler control effort. For example, the steady nature of a conventional bicopter contributes to capabilities such as close inspections and steady mode video transmission. Additionally, the smaller footprint while hovering allows maneuvering through small or narrow spaces. However, conventional bicopters are less power/energy efficient than conventional monocopters, for example, since conventional bicopters are not configured to auto-rotate. In addition, conventional bicopters may bear a resemblance to a tailsitter, which may be particularly good for its efficiency in a forward-flight mode, however, owing to its forward velocity, the forward-flight mode may not be suitable for operations within a confined space. Furthermore, the tailsitter would simply crash during a fail-safe scenario, however, the monocopter mode can achieve a softer landing, comparatively. Accordingly, the monocopter mode and the bicopter mode have different advantages/benefits and disadvantages/limitations. [0009] A need therefore exists to provide a single-wing rotorcraft (which may also be referred to as a single-wing aerial vehicle or robot) with multiple flight modes, including a monocopter mode and a bicopter mode, that seeks to overcome, or at least ameliorate, one or more deficiencies in conventional rotorcrafts with (only) a single flight mode, and more particularly, provide a single-wing rotorcraft with multiple flight modes in an effective manner for enabling the single-wing rotorcraft to be adaptable in an operating environment during flight and be employable in a wider range of practical applications. It is against this background that the present invention has been developed. SUMMARY

[0010] According to a first aspect of the present invention, there is provided a single-wing rotorcraft with multiple flight modes, comprising: a frame member; a wing member coupled to the frame member; a flap member rotatably coupled to the frame member; a first thrust unit rotatably coupled to the frame member at a first portion thereof and configured to generate a first thrust; a second thrust unit rotatably coupled to the frame member at a second portion thereof and configured to generate a second thrust, the first and second portions being separated along the frame member by a distance; a first actuator configured to rotate the first thrust unitabout the frame member with respect to the wing member; a second actuator configured to rotate the second thrust unit and the flap member about the frame member with respect to the wing member; and a flight controller communicatively coupled to the first and second thrust units and the first and second actuators and configured to control, in response to a transition control signal received, the single-wing rotorcraft to transition from one flight mode to another flight mode amongst the multiple flight modes during flight based on the first and second thrust units and the first and second actuators, the multiple flight modes comprising a monocopter mode and a bicopter mode.

[0011] According to a second aspect of the present invention, there is provided a method of operating the single-wing rotorcraft according to the above-mentioned first aspect of the present invention, the method comprising: receiving, by the flight controller, the transition control signal to instruct the flight controller to transition the single-wing rotorcraft from the monocopter mode to the bicopter mode or from the bicopter mode to the monocopter mode; and controlling, by the mode transition controller in response to the transition control signal received, the first and second actuators and the first and second thrust units during the transition phase to transition the single-wing rotorcraft from one flight mode to another flight mode amongst the multiple flight modes during flight. [0012] According to a third aspect of the present invention, there is provided a method of forming a single-wing rotorcraft with multiple flight modes (e.g., the single-wing rotorcraft according to the above-mentioned first aspect of the present invention), the method comprising: providing or forming a frame member; providing or forming a wing member coupled to the frame member; providing or forming a flap member rotatably coupled to the frame member; providing or forming a first thrust unit rotatably coupled to the frame member at a first portion thereof and configured to generate a first thrust; providing or forming a second thrust unit rotatably coupled to the frame member at a second portion thereof and configured to generate a second thrust, the first and second portions being separated along the frame member by a distance; providing or forming a first actuator configured to rotate the first thrust unit about the frame member with respect to the wing member; providing or forming a second actuator configured to rotate the second thrust unit and the flap member about the frame member with respect to the wing member; and providing or forming a flight controller communicatively coupled to the first and second thrust units and the first and second actuators and configured to control, in response to a transition control signal received, the single-wing rotorcraft to transition from one flight mode to another flight mode amongst the multiple flight modes during flight based on the first and second thrust units and the first and second actuators, the multiple flight modes comprising a monocopter mode and a bicopter mode.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Embodiments of the present invention will be better understood and readily apparent to one of ordinary skill in the art from the following written description, by way of example only, and in conjunction with the drawings, in which:

FIG. 1 depicts a schematic drawing of a single-wing rotorcraft with multiple flight modes, according to various embodiments of the present invention;

FIG. 2 depicts a schematic flow diagram of a method of operating the single-wing rotorcraft, according to various embodiments of the present invention;

FIG. 3 depicts a schematic block diagram of a flight controller configured to control, in response to a transition control signal received, the single-wing rotorcraft to transition from one flight mode to another flight mode amongst the multiple flight modes during flight, according to various embodiments of the present invention;

FIG. 4 depicts a schematic flow diagram of a method of forming a single-wing rotorcraft with multiple flight modes, according to various embodiments the present invention;

FIGs. 5 A to 5D depict schematic drawings of an example single-wing rotorcraft (which may be referred to as an unmanned aerial vehicle (UAV)) with multiple flight modes at different views, according to various example embodiments of the present invention;

FIG. 6 depicts a schematic block diagram of an example flight controller of the UAV, according to various example embodiments of the present invention;

FIG. 7 depicts plots of example thrust and actuator output commands/signals output from the mode transition controller for the transition of the UAV (1) from the B-mode to the M-mode and (2) from the M-mode to the B-mode, according to various example embodiments of the present invention;

FIG. 8 illustrates example transitions of the UAV between the B-mode to the M-mode (from the B-mode to the M-mode and vice versa), according to various example embodiments of the present invention, along with various stages encountered during the transitions;

FIG. 9 depicts a front or top view and a back or bottom view of an example physical prototype of the UAV, according to various example embodiments of the present invention;

FIG. 10 shows a Table (Table 2) presenting various dimensional and gain parameters associated with the UAV, along with their example numerical values, according to various example embodiments of the present invention;

FIGs. 11 A and 1 IB show pictures of the UAV during experimental flight in the M-mode and the B-mode (flying through a narrow opening), respectively, according to various example embodiments of the present invention;

FIG. 12 shows plots comparing the power consumption of the UAV when hovering in the M-mode and the B-mode, according to various example embodiments of the present invention;

FIG. 13 shows plots of the Euler angles of the UAV during the M-mode and B-mode flights, according to various example embodiments of the present invention;

FIGs. 14A and 15A depict plots of the desired position (Xd, Yd, Zd) and the actual position (X, Y, Z) of the UAV, along with the thrust and actuator output commands/signals, while performing square shaped waypoint tracking (FIG. 14 A) and while performing circular trajectory tracking (FIG. 15 A), respectively, for the M-mode flight, according to various example embodiments of the present invention;

FIGs. 14B and 15B depict plots of the desired position (Xd, Yd, Zd) and the actual position (X, Y, Z) of the UAV, along with the thrust and actuator output commands/signals, while performing square shaped waypoint tracking (FIG. 14B) and while performing circular trajectory tracking (FIG. 15B), respectively, for the B-mode flight, according to various example embodiments of the present invention;

FIG. 16 depicts plots of the angular velocity and the attitude of the UAV during the transition from the B-mode to the M-mode and then back to the B-mode, according to various example embodiments of the present invention; and

FIGs. 17A and 17B depict the thrust and actuator output commands/signals output from the mode transition controller for controlling the first thrust unit (‘Motorl’, the second thrust unit (‘Motor2'), the first actuator (‘Servol’) and the second actuator (‘Servo2’) during the transition from the B-mode to the M-mode and then back to the B-mode, according to various example embodiments of the present invention.

DETAILED DESCRIPTION

[0014] Various embodiments of the present invention provide a single-wing rotorcraft (which may also be referred to herein as a single-wing aerial vehicle or robot), a method of operating the single-wing rotorcraft and a method of forming the single-wing rotorcraft, and more particularly, a single-wing rotorcraft with multiple flight modes, including a monocopter mode and a bicopter mode. In this regard, the multiple flight modes are different types of flight modes, including monocopter and bicopter modes.

[0015] As discussed in the background, different types of flight modes, such as monocopter and bicopter modes, have different advantages/benefits and disadvantages/limitations. Accordingly, conventional rotorcrafts with (only) a single flight mode suffers from various limitations or deficiencies. In this regard, various embodiments of the present invention provide a single-wing rotorcraft with multiple flight modes, including a monocopter mode and a bicopter mode, that seeks to overcome, or at least ameliorate, one or more deficiencies in conventional rotorcrafts with a single flight mode, and more particularly, provide a single-wing rotorcraft with multiple flight modes in an effective manner for enabling the single-wing rotorcraft to be adaptable in an operating environment during flight and be employable in a wider range of practical applications. [0016] FIG. 1 depicts a schematic drawing of a single-wing rotorcraft 100 with multiple flight modes according to various embodiments of the present invention. The single-wing rotorcraft 100 comprises: a frame member 110; a wing member 120 coupled (e.g., rigidly/non- rotatably attached/affixed) to the frame member 110; a flap member 122 rotatably coupled to the frame member 110; a first thrust unit 130 rotatably coupled to the frame member 110 at a first portion 112 thereof and configured to generate a first thrust; and a second thrust unit 132 rotatably coupled to the frame member 110 at a second portion 114 thereof and configured to generate a second thrust. In this regard, the first and second portions 112, 114 are separated along the frame member 110 by a distance. The single-wing rotorcraft 100 further comprises a first actuator 140 configured to rotate the first thrust unit 130 about the frame member 110 with respect to (or relative to) the wing member 120, and a second actuator 142 configured to rotate the second thrust unit 132 and the flap member 122 about the frame member 110 with respect to (or relative to) the wing member 120. In particular, the single-wing rotorcraft 100 comprises a flight controller 150 communicatively coupled to the first and second thrust units 130, 132 and the first and second actuators 140, 142 and configured to control, in response to a transition control signal received, the single-wing rotorcraft 100 to transition from one flight mode to another flight mode amongst the multiple flight modes during flight based on the first and second thrust units 130, 132 and the first and second actuators 140, 142. In this regard, the multiple flight modes comprising a monocopter mode and a bicopter mode.

[0017] In various embodiments, the monocopter mode is a flight mode whereby the flight of the rotorcraft (e.g., lift thereof) is primarily achieved by rotating/ spinning the entire rotorcraft (with its single wing member (e.g., single rotating blade)) about its yaw axis, such as but not limited to, the flight mode of conventional monocopters as described in the background. The bicopter mode is a flight mode whereby the flight of the rotorcraft (e.g., lift thereof) is primarily achieved by two thrust units (e.g., two motor-driven propellers) without rotating/spinning the entire rotorcraft about its yaw axis, such as but not limited to, the flight mode of conventional bicopters as described in the background.

[0018] Accordingly, the single-wing rotorcraft 100 according to various embodiments of the present invention is advantageously capable of multiple flight modes (i.e., different types of flight modes, including the monocopter and bicopter modes). Furthermore, the single-wing rotorcraft 100 with multiple flight modes is provided in an effective manner. In particular, not only is the single-wing rotorcraft 100 capable of multiple flight modes, the single-wing rotorcraft 100 comprises a flight controller 150 configured to control, in response to a transition control signal received, the single-wing rotorcraft 100 to transition from one flight mode to another flight mode amongst the multiple flight modes during flight in an effective manner, and more particularly, based on controlling the first and second thrust units 130, 132 and the first and second actuators 140, 142 during a transition phase. Accordingly, the single-wing rotorcraft 100 is advantageously able to adapt in an operating environment during flight (e.g., set or transition to monocopter mode when power/energy efficiency is desired and set or transition to bicopter mode when flight stability is desired) and be employable in a wider range of practical applications. These advantages or technical effects, and/or other advantages or technical effects, will become more apparent to a person skilled in the art as the single-wing rotorcraft 100 is described in more detail according to various embodiments and example embodiments of the present invention.

[0019] In various embodiments, the second actuator 142 is coupled to the second thrust unit 132 and the flap member 122 (e.g., via a servo horn) for rotating the second thrust unit 132 and the flap member 122 about the frame member 110 with respect to (or relative to) the wing member 120.

[0020] In various embodiments, the second thrust unit 132 has a fixed relationship with the flap member 122, and the second actuator 142 is configured to rotate the second thrust unit 132 and the flap member 122 together about the frame member 110 with respect to the wing member 120. That is, the second thrust unit 132 and the flap member 122 are arranged/configured to have a fixed relationship with respect to each other (e.g., rigidly affixed/attached to each other) and the orientation of the second thrust unit 132 and the flap member 122 (collectively) about the frame member 110 is controllable/adjustable by the second actuator 142.

[0021] In various embodiments, the first actuator 140 is coupled to the first thrust unit 130 (e.g., via a servo horn) for rotating the first thrust unit 130 about the frame member 110 with respect to (or relative to) the wing member 120. In various embodiments, the first and second actuators 140, 142 are coupled to the wing member 120 at opposite edge portions of the wing member 120.

[0022] In various embodiments, the single-wing rotorcraft 100 further comprises a housing member coupled (e.g., rigidly/non-rotatably attached/affixed) to the frame member 110. In various embodiments, the flight controller 150 is disposed on the housing member (thereby housing the flight controller 150). Moreover, the housing member is arranged between the first actuator 140 and the wing member 120, and the first actuator 140 is coupled to the wing member 120 via the housing member. In this regard, the first actuator 140 may be directly coupled to the housing member, and the housing member may in turn be directly coupled to the wing member 120. Therefore, the first actuator 140 may be indirectly coupled to the wing member 120 (via the housing member). For example, various electrical/electronic components may be disposed on the housing member as desired or as appropriate, and the housing member may also be referred to as a board member (e.g., a printed circuit board).

[0023] In various embodiments, the second thrust unit 132 is configured to generate the second thrust in a direction at least substantially perpendicular to the second portion 114 of the frame member 110 and at least substantially opposite to a direction in which the flap member 122 extends from the second portion 114 of the frame member 110. In various embodiments, the first thrust unit 130 is configured to generate the first thrust in a direction at least substantially perpendicular to the first portion 112 of the frame member 110.

[0024] In various embodiments, the first and second thrust units 130, 132 are arranged at a first side of the frame member 110, and the wing member 120 and the flap member 122 are arranged at a second side of the frame member 110. In this regard, the first and second sides of the frame member 110 are opposite sides.

[0025] In various embodiments, the frame member 110 is a rod. In this regard, the wing member 120 and the flap member 122 are arranged adjacent to each other (and nonoverlapping) along the rod 110 such that, in a non-actuated state, a plane (planar cross-section) of the wing member 120 and a plane (planar cross-section) of the flap member 122 are at least substantially along a same plane.

[0026] In various embodiments, the above-mentioned first and second portions 112, 114 of the frame member 110 may be inner/proximal portion and outer/distal portion of the frame member 110, respectively. For example, the inner/proximal portion and outer/distal portion of the frame member 110 may be with respect to a rotating axis (yaw axis) of the single-wing rotorcraft 100 in the monocopter mode.

[0027] In various embodiments, the flight controller 150 comprises: a monocopter mode controller configured to control a flight of the single-wing rotorcraft 100 in the monocopter mode; a bicopter mode controller configured to control a flight of the single-wing rotorcraft 100 in the bicopter mode; and a mode transition controller communicatively coupled to the monocopter mode controller and the bicopter mode controller and configured to control, in response to the transition control signal received, the first and second actuators 140, 142 and the first and second thrust units 130, 132 during a transition phase to transition the single-wing rotorcraft 100 from one flight mode to another flight mode amongst the multiple flight modes during flight. In this regard, the transition control signal received is to instruct the flight controller 150 to transition the single-wing rotorcraft 100 from the monocopter mode to the bicopter mode or from the bicopter mode to the monocopter mode. In this regard, the mode transition controller advantageously enhances the transition from one flight mode to another flight mode in an effective manner. In particular, instead of merely implementing an on-off approach (e.g., simply turning on/off the monocopter/bicopter mode to transition from one flight mode to another flight mode), the mode transition controller is configured to control the first and second thrust units 130, 132 during the transition phase to enhance the transition from one flight mode to another flight mode in an effective manner. In various embodiments, the mode transition controller is further configured to control the first and second actuators 140, 142 during the transition phase to further enhance the transition from one flight mode to another flight mode in an effective manner.

[0028] In various embodiments, the mode transition controller is configured to, in response to the transition control signal received being to instruct the flight controller 150 to transition the single-wing rotorcraft 100 from the monocopter mode to the bicopter mode, control, during a first stage (or an initial stage) of the transition phase, the first actuator 140 to rotate, in a clockwise direction, the first thrust unit 130 about the frame member 110 with respect to (or relative to) the wing member 120 and the second actuator 132 to rotate, in the clockwise direction, the second thrust unit 132 and the flap member 122 about the frame member 110 with respect to (or relative to) the wing member 120 so as to increase a relative angle in the clockwise direction from a plane of the wing member 120 to a direction of the first thrust generated by the first thrust unit 130 (i.e., the relative angle in the clockwise direction between the plane of the wing member 120 and the direction of the first thrust) and to increase a relative angle in the clockwise direction from the plane of the wing member 120 to a plane of the flap member 122 and a direction of the second thrust generated by the second thrust unit 132 (i.e., the relative angle in the clockwise direction between the plane of the wing member 120 and the plane of the flap member 122 (as well as the direction of the second thrust) (in this regard, the direction of the second thrust is along (in) the plane of the flap member 122)) for increasing a pitch of (pitching up) the first and second thrust units 130, 132 and the flap member 122 so as to stall the wing member 120 (e.g., pitching up the single-wing rotorcraft 100 decreases its rotational speed). In this regard, the clockwise direction is when viewed in a direction along the frame member 110 from the first thrust unit 130 to the second thrust unit 132. In various embodiments, the mode transition controller is further configured to, in response to the transition control signal received being to instruct the flight controller 150 to transition the single-wing rotorcraft 100 from the monocopter mode to the bicopter mode, control, during the first stage of the transition phase, the first thrust unit 130 to increase the first thrust generated by the first thrust unit 130 and the second thrust unit 132 to decrease the second thrust generated by the second thrust unit 132.

[0029] In various embodiments, the mode transition controller is further configured to, in response to the transition control signal received being to instruct the flight controller 150 to transition the single-wing rotorcraft 100 from the monocopter mode to the bicopter mode, control the first and second thrust units 130, 132 during the transition phase based on a first function configured to phase out a second thrust control signal produced based on the monocopter mode controller for controlling the second thrust unit 132 and to phase in a first thrust control signal and a second thrust control signal produced based on the bicopter mode controller for controlling the first and second thrust units 130, 132, respectively. In various embodiments, the first function is a sigmoid function.

[0030] In various embodiments, the mode transition controller is further configured to, in response to the transition control signal received being to instruct the flight controller 150 to transition the single-wing rotorcraft 100 from the monocopter mode to the bicopter mode, control the first and second actuators 140, 142 during the transition phase based on the first function configured to further phase out a second actuator control signal produced based on the monocopter mode controller for controlling the second actuator 142 and to phase in a first actuator control signal and a second actuator control signal produced based on the bicopter mode controller for controlling the first and second actuators 140, 142, respectively.

[0031] Accordingly, in various embodiments, when transitioning the single-wing rotorcraft 100 from the monocopter mode to the bicopter mode, the mode transition controller does not simply switch off the monocopter mode and switch on the bicopter mode, but controls the first and second actuators 140, 142 and the first and second thrust units 130, 132 in the manner as described herein according to various embodiments to advantageously enhance the transition from the monocopter mode to the bicopter mode in an effective manner.

[0032] In various embodiments, the mode transition controller is configured to, in response to the transition control signal received being to instruct the flight controller 150 to transition the single-wing rotorcraft 100 from the bicopter mode to the monocopter mode, control, during a first stage (or an initial stage) of the transition phase, the first actuator 140 to rotate, in an anticlockwise direction, the first thrust unit 130 about the frame member 110 with respect to (or relative to) the wing member 120 and the second actuator 142 to rotate, in the anti-clockwise direction, the second thrust unit 132 and the flap member 122 about the frame member 110 with respect to (or relative to) the wing member 120 so as to increase a relative angle in the anticlockwise direction from a plane of the wing member 120 to a direction of the first thrust generated by the first thrust unit 130 (i.e., the relative angle in the anti-clockwise direction between the plane of the wing member 120 and the direction of the first thrust) and to increase a relative angle in the anti -clockwise direction from the plane of the wing member 120 to a plane of the flap member 122 and a direction of the second thrust generated by the second thrust unit 132 (i.e., the relative angle in the anti-clockwise direction between the plane of the wing member 120 and the plane of the flap member 122 (as well as the direction of the second thrust) (in this regard, the direction of the second thrust is along (in) the plane of the flap member 122)) for decreasing a pitch of (pitching down) the first and second thrust units 130, 132 and the flap member 122. In this regard, the anti-clockwise direction is when viewed in a direction along the frame member 110 from the first thrust unit 130 to the second thrust unit 132. In various embodiments, the mode transition controller is further configured to, in response to the transition control signal received being to instruct the flight controller 150 to transition the single-wing rotorcraft 100 from the bicopter mode to the monocopter mode, control, during the first stage of the transition phase, the first thrust unit 130 to decrease the first thrust generated by the first thrust unit 130 and the second thrust unit 132 to increase the second thrust generated by the second thrust unit 132 (e.g., which has been found to induce rotational motion in the anti -clockwise direction for transitioning to the monocopter mode).

[0033] In various embodiments, the mode transition controller is further configured to, in response to the transition control signal received being to instruct the flight controller 150 to transition the single-wing rotorcraft 100 from the bicopter mode to the monocopter mode, control the first and second thrust units 130, 132 during the transition phase based on a second function configured to phase out a first thrust control signal and a second thrust control signal produced based on the bicopter mode controller for controlling the first and second thrust units 130, 132, respectively, and to phase in a second thrust control signal produced based on the monocopter mode controller for controlling the second thrust unit 132. In various embodiments, the second function is a sigmoid function.

[0034] In various embodiments, the mode transition controller is further configured to, in response to the transition control signal received being to instruct the flight controller 150 to transition the single-wing rotorcraft 100 from the bicopter mode to the monocopter mode, control the first and second actuators 140, 142 during the transition phase based on the second function configured to further phase out a first actuator control signal and a second actuator control signal produced based on the bicopter mode controller for controlling the first and second actuators 140, 142, respectively, and to phase in a second actuator control signal produced based on the monocopter mode controller for controlling the second actuator 142.

[0035] Accordingly, in various embodiments, when transitioning the single-wing rotorcraft 100 from the bicopter mode to the monocopter mode, the mode transition controller does not simply switch off the bicopter mode and switch on the monocopter mode, but controls the first and second actuators 140, 142 and the first and second thrust units 130, 132 in the manner as described herein according to various embodiments to advantageously enhance the transition from the bicopter mode to the monocopter mode in an effective manner.

[0036] In various embodiments, the first and second thrust units 130, 132 may each comprise a propeller and a motor configured to rotate the propeller. It will be appreciated by a person skilled in the art that the present invention is not limited to any particular type of thrust unit for the first and second thrust units 130, 132 as long as the thrust unit is capable of being operated to generate thrust to facilitate or support a flight of the single-wing rotorcraft 100 as described herein according to various embodiments. It will also be appreciated by a person skilled in the art that the present invention is not limited to any particular type of actuator for the first and second actuators 140, 142 as long as the actuator is capable of being configured, or being operated, to rotate the first and second thrust units 130, 132 and the flap member 122 about the frame member 110 as described herein according to various embodiments. Furthermore, it will be appreciated by a person skilled in the art that the wing member 120 and the flap member 122 may each be configured to have any configuration or any shape as desired or as appropriate, as long as the single-wing rotorcraft 100 can operate in multiple flight modes, including the monocopter and bicopter flight modes, as described herein according to various embodiments. Accordingly, the wing member 120 and the flap member 122 is not limited to any particular configuration or shape.

[0037] FIG. 2 depicts a schematic flow diagram of a method 200 of operating the singlewing rotorcraft 100 according to various embodiments of the present invention. As described hereinbefore according to various embodiments, the flight controller 150 comprises: a monocopter mode controller configured to control a flight of the single-wing rotorcraft 100 in the monocopter mode; a bicopter mode controller configured to control a flight of the singlewing rotorcraft 100 in the bicopter mode; and a mode transition controller communicatively coupled to the monocopter mode controller and the bicopter mode controller and configured to control, in response to the transition control signal received, the first and second actuators 140, 142 and the first and second thrust units 130, 132 during a transition phase to transition the single-wing rotorcraft 100 from one flight mode to another flight mode amongst the multiple flight modes during flight. In this regard, the transition control signal received is to instruct the flight controller 150 to transition the single-wing rotorcraft 100 from the monocopter mode to the bicopter mode or from the bicopter mode to the monocopter mode.

[0038] In various embodiments, the method 200 comprises: receiving (at 206), by the flight controller 150, the transition control signal to instruct the flight controller 150 to transition the single-wing rotorcraft 100 from the monocopter mode to the bicopter mode or from the bicopter mode to the monocopter mode; and controlling (at 208), by the mode transition controller in response to the transition control signal received, the first and second actuators 140, 142 and the first and second thrust units 130, 132 during the transition phase to transition the singlewing rotorcraft 100 from one flight mode to another flight mode amongst the multiple flight modes during flight.

[0039] In various embodiments, the above-mentioned controlling (at 208), by the mode transition controller in response to the transition control signal received being to instruct the flight controller 150 to transition the single-wing rotorcraft 100 from the monocopter mode to the bicopter mode, comprises controlling, during a first stage (or an initial stage) of the transition phase, the first actuator 140 to rotate, in a clockwise direction, the first thrust unit 130 about the frame member 110 with respect to (or relative to) the wing member 120 and the second actuator 132 to rotate, in the clockwise direction, the second thrust unit 132 and the flap member 122 about the frame member 110 with respect to (or relative to) the wing member 120 so as to increase a relative angle in the clockwise direction from a plane of the wing member 120 to a direction of the first thrust generated by the first thrust unit 130 (i.e., the relative angle in the clockwise direction between the plane of the wing member 120 and the direction of the first thrust) and to increase a relative angle in the clockwise direction from the plane of the wing member 120 to a plane of the flap member 122 and a direction of the second thrust generated by the second thrust unit 132 (i.e., the relative angle in the clockwise direction between the plane of the wing member 120 and the plane of the flap member 122 (as well as the direction of the second thrust) (in this regard, the direction of the second thrust is along (in) the plane of the flap member 122)) for increasing a pitch of (pitching up) the first and second thrust units 130, 132 and the flap member 122 so as to stall the wing member 120 (e.g., pitching up the single-wing rotorcraft 100 decreases its rotational speed). In this regard, the clockwise direction is when viewed in a direction along the frame member 110 from the first thrust unit 130 to the second thrust unit 132. In various embodiments, the above-mentioned controlling (at 208), by the mode transition controller in response to the transition control signal received being to instruct the flight controller 150 to transition the single-wing rotorcraft 100 from the monocopter mode to the bicopter mode, further comprises controlling, during the first stage of the transition phase, the first thrust unit 130 to increase the first thrust generated by the first thrust unit 130 and the second thrust unit 132 to decrease the second thrust generated by the second thrust unit 132.

[0040] In various embodiments, the above-mentioned controlling (at 208), by the mode transition controller in response to the transition control signal received being to instruct the flight controller 150 to transition the single-wing rotorcraft from the monocopter mode to the bicopter mode, further comprises controlling the first and second thrust units 130, 132 during the transition phase based on a first function configured to phase out a second thrust control signal produced based on the monocopter mode controller for controlling the second thrust unit 132 and to phase in a first thrust control signal and a second thrust control signal produced based on the bicopter mode controller for controlling the first and second thrust units 130, 132, respectively. In various embodiments, the first function is a sigmoid function.

[0041] In various embodiments, the above-mentioned controlling (at 208), by the mode transition controller in response to the transition control signal received being to instruct the flight controller 150 to transition the single-wing rotorcraft 100 from the monocopter mode to the bicopter mode, further comprises controlling the first and second actuators 140, 142 during the transition phase based on the first function configured to further phase out a second actuator control signal produced based on the monocopter mode controller for controlling the second actuator 142 and to phase in a first actuator control signal and a second actuator control signal produced based on the bicopter mode controller for controlling the first and second actuators 140, 142, respectively.

[0042] In various embodiments, the method 200 further comprises controlling, by the mode transition controller after phasing out the second thrust control signal and the second actuator control signal produced based on the monocopter mode controller: the first and second actuators 140, 142 based on the first and second actuator control signals produced based on the bicopter mode controller for controlling the first and second actuators 140, 142, respectively; and the first and second thrust units 130, 132 based on the first and second thrust control signals produced based on the bicopter mode controller for controlling the first and second thrust units 130, 132, respectively, thereby completing the transition of the single-wing rotorcraft 100 from the monocopter mode to the bicopter mode.

[0043] In various embodiments, the above-mentioned controlling (at 208), by the mode transition controller in response to the transition control signal received being to instruct the flight controller 150 to transition the single-wing rotorcraft 100 from the bicopter mode to the monocopter mode, comprises controlling, during a first stage (or an initial stage) of the transition phase, the first actuator 140 to rotate, in an anti-clockwise direction, the first thrust unit 130 about the frame member 110 with respect to (or relative to) the wing member 120 and the second actuator 142 to rotate, in the anti-clockwise direction, the second thrust unit 132 and the flap member 122 about the frame member 110 with respect to (or relative to) the wing member 120 so as to increase a relative angle in the anti-clockwise direction from a plane of the wing member 120 to a direction of the first thrust generated by the first thrust unit 130 (i.e., the relative angle in the anti-clockwise direction between the plane of the wing member 120 and the direction of the first thrust) and to increase a relative angle in the anti-clockwise direction from the plane of the wing member 120 to a plane of the flap member 122 and a direction of the second thrust generated by the second thrust unit 132 (i.e., the relative angle in the anti-clockwise direction between the plane of the wing member 120 and the plane of the flap member 122 (as well as the direction of the second thrust) (in this regard, the direction of the second thrust is along (in) the plane of the flap member 122)) for decreasing a pitch of (pitching down) the first and second thrust units 130, 132 and the flap member 122. In this regard, the anti -clockwise direction is when viewed in a direction along the frame member 110 from the first thrust unit 130 to the second thrust unit 132. In various embodiments, the above- mentioned controlling (at 208), by the mode transition controller in response to the transition control signal received being to instruct the flight controller 150 to transition the single-wing rotorcraft 100 from the monocopter mode to the bicopter mode, further comprises controlling, during the first stage of the transition phase, the first thrust unit 130 to decrease the first thrust generated by the first thrust unit 130 and the second thrust unit 132 to increase the second thrust generated by the second thrust unit 132 (e.g., which has been found to induce rotational motion in the anti-clockwise direction for transitioning to the monocopter mode).

[0044] In various embodiments, the above-mentioned controlling (at 208), by the mode transition controller in response to the transition control signal received being to instruct the flight controller to transition the single-wing rotorcraft from the bicopter mode to the monocopter mode, further comprises: controlling the first and second thrust units 130, 132 during the transition phase based on a second function configured to phase out a first thrust control signal and a second thrust control signal produced based on the bicopter mode controller for controlling the first and second thrust units 130, 132, respectively, and to phase in a second thrust control signal produced based on the monocopter mode controller for controlling the second thrust unit 132. In various embodiments, the second function is a sigmoid function.

[0045] In various embodiments, the above-mentioned controlling (at 208), by the mode transition controller in response to the transition control signal received being to instruct the flight controller 150 to transition the single-wing rotorcraft 100 from the bicopter mode to the monocopter mode, further comprises, controlling the first and second actuators 140, 142 during the transition phase based on the second function configured to further phase out a first actuator control signal and a second actuator control signal produced based on the bicopter mode controller for controlling the first and second actuators 140, 142, respectively, and to phase in a second actuator control signal produced based on the monocopter mode controller for controlling the second actuator 142.

[0046] In various embodiments, the method 200 further comprises controlling, by the mode transition controller after phasing out the first and second thrust control signals and the first and second actuator control signals produced based on the bicopter mode controller: the second actuator 142 based on the second actuator control signal produced based on the monocopter mode controller for controlling the second actuator 142; and the second thrust unit 132 based on the second thrust control signal produced based on the monocopter mode controller for controlling the second thrust unit 132, thereby completing the transition of the single-wing rotorcraft 100 from the bicopter mode to the monocopter mode.

[0047] It will be appreciated by a person skilled in the art that the method 200 of operating the single-wing rotorcraft 100 may further comprise additional or other operation(s) corresponding to operation(s) in which the single-wing rotorcraft 100 (e.g., components/modules thereof) is configured to perform as described herein according to various embodiments of the present invention, and thus such corresponding additional or other operations need not be repeated with respect to the method 200 of operating the single-wing rotorcraft 100 for clarity and conciseness. In other words, various embodiments described herein in context of the single-wing rotorcraft 100 are analogously valid for the method 200 of operating the single-wing rotorcraft 100, and vice versa. [0048] FIG. 3 depicts a schematic block diagram of the flight controller 150 configured to control, in response to a transition control signal received, the single-wing rotorcraft 100 to transition from one flight mode to another flight mode amongst the multiple flight modes during flight according to various embodiments of the present invention. The flight controller 150 comprises: at least one memory 302; and at least one processor 304 communicatively coupled to the at least one memory 302 and configured to perform the above-mentioned method 200 of operating the single-wing rotorcraft 100 as described herein according with reference to FIG. 2 according to various embodiments of the present invention. Accordingly, the at least one processor 304 is configured to: receive the transition control signal to instruct the flight controller 150 to transition the single-wing rotorcraft 100 from the monocopter mode to the bicopter mode or from the bicopter mode to the monocopter mode; and control, in response to the transition control signal received, the first and second actuators 140, 142 and the first and second thrust units 130, 132 during the transition phase to transition the single-wing rotorcraft 100 from one flight mode to another flight mode amongst the multiple flight modes during flight.

[0049] It will be appreciated by a person skilled in the art that the at least one processor 304 may be configured to perform various functions or operations through set(s) of instructions (e.g., software modules) executable by the at least one processor 304 to perform various functions or operations. Accordingly, as shown in FIG. 3, the flight controller 150 may comprise: a transition control signal receiving module 306 (or a transition control signal receiving circuit) configured to receive the transition control signal to instruct the flight controller 150 to transition the single-wing rotorcraft 100 from the monocopter mode to the bicopter mode or from the bicopter mode to the monocopter mode; and a mode transition controller 308 (or a mode transition control module or circuit) configured to control, in response to the transition control signal received, the first and second actuators 140, 142 and the first and second thrust units 130, 132 during the transition phase to transition the single-wing rotorcraft 100 from one flight mode to another flight mode amongst the multiple flight modes during flight. In various embodiments, the flight controller 150 may further comprise a monocopter mode controller 310 (e.g., a monocopter mode control module or circuit) configured to control a flight of the single-wing rotorcraft 100 in the monocopter mode; and a bicopter mode controller 312 (e.g., a bicopter mode control module or circuit) configured to control a flight of the single-wing rotorcraft 100 in the bicopter mode. In this regard, the mode transition controller 308 (e.g., a mode transition control module or circuit) may be communicatively coupled to the monocopter mode controller 310 and the bicopter mode controller 312. It will be appreciated by a person skilled in the art that various components of the flight controller 150 may communicate via an interconnected bus 305.

[0050] It will be appreciated by a person skilled in the art that the transition control signal receiving module 306, the mode transition controller 308, the monocopter mode controller 310 and the bicopter mode controller 312 and are not necessarily separate modules, and they may be realized by or implemented as one functional module (e.g., a circuit or a software program) as desired or as appropriate without deviating from the scope of the present invention. For example, the transition control signal receiving module 306, the mode transition controller 308, the monocopter mode controller 310 and/or the bicopter mode controller 312 may be realized (e.g., compiled together) as one executable software program (e.g., software application or simply referred to as an “app”), which for example may be stored in the at least one memory 302 and executable by the at least one processor 304 to perform various functions/operations as described herein according to various embodiments of the present invention.

[0051] In various embodiments, the flight controller 150 corresponds to the method 200 of operating the single-wing rotorcraft 100 as described hereinbefore with reference to FIG. 2 according to various embodiments, therefore, various operations, functions or steps configured to be performed by the at least one processor 304 may correspond to various operations, functions or steps of the method 200 of operating the single-wing rotorcraft 100 as described herein according to various embodiments, and thus need not be repeated with respect to the flight controller 150 for clarity and conciseness. In other words, various embodiments described herein in context of the methods are analogously valid for the corresponding systems (e.g., the flight controller 150), and vice versa.

[0052] For example, in various embodiments, the at least one memory 302 may have stored therein the transition control signal receiving module 306, the mode transition controller 308, the monocopter mode controller 310 and/or the bicopter mode controller 312, which are configured to perform, or correspond to, various operations, functions or steps of the method 200 of operating the single-wing rotorcraft 100 as described herein according to various embodiments, which are executable by the at least one processor 304 to perform the corresponding operations, functions or steps as described herein. For example, in various embodiments, the transition control signal receiving module 306 is configured to perform the above-mentioned receiving (at 202) the transition control signal. For example, in various embodiments, the mode transition controller 308 is configured to perform the above-mentioned controlling (at 204), in response to the transition control signal received, the first and second actuators 140, 142 and the first and second thrust units 130, 132 during the transition phase to transition the single-wing rotorcraft 100 from one flight mode to another flight mode amongst the multiple flight modes during flight. In this regard, the mode transition controller 308 may be configured to control the first and second actuators 140, 142 and the first and second thrust units 130, 132 during the transition phase as described herein according to various embodiments.

[0053] Any computing system or device providing a processing capability may be provided according to various embodiments of the present invention. Such a computing system or device may be taken to include one or more processors and one or more computer-readable storage mediums. A memory or computer-readable storage medium used in various embodiments may be a volatile memory, for example a DRAM (Dynamic Random Access Memory) or a nonvolatile memory, for example a PROM (Programmable Read Only Memory), an EPROM (Erasable PROM), EEPROM (Electrically Erasable PROM), or a flash memory, e.g., a floating gate memory, a charge trapping memory, an MRAM (Magnetoresistive Random Access Memory) or a PCRAM (Phase Change Random Access Memory).

[0054] In various embodiments, a “circuit” may be understood as any kind of a logic implementing entity, which may be special purpose circuitry or a processor executing software stored in a memory, firmware, or any combination thereof. Thus, in an embodiment, a “circuit” may be a hard-wired logic circuit or a programmable logic circuit such as a programmable processor, e.g., a microprocessor (e.g., a Complex Instruction Set Computer (CISC) processor or a Reduced Instruction Set Computer (RISC) processor). A “circuit” may also be a processor executing software, e.g., any kind of computer program, e.g., a computer program using a virtual machine code, e.g., Java. Any other kind of implementation of various functions or operations may also be understood as a “circuit” in accordance with various other embodiments. Similarly, a “module” may be a portion of a system according to various embodiments of the present invention and may encompass a “circuit” as above, or may be understood to be any kind of a logic-implementing entity therefrom.

[0055] Some portions of the present disclosure may be explicitly or implicitly presented in terms of algorithms and functional or symbolic representations of operations on data within a computer memory. These algorithmic descriptions and functional or symbolic representations are the means used by those skilled in the data processing arts to convey most effectively the substance of their work to others skilled in the art. An algorithm is here, and generally, conceived to be a self-consistent sequence of steps leading to a desired result. The steps are those requiring physical manipulations of physical quantities, such as electrical, magnetic or optical signals capable of being stored, transferred, combined, compared, and otherwise manipulated.

[0056] It will be appreciated by a person skilled in the art that the flight controller 150 may be specially constructed for the required purposes, or may comprise a general purpose computing device selectively activated or reconfigured by computer program(s) stored in the computing device. In general, various algorithms that may be presented herein are not limited to being implemented or executed by any particular computer system. Alternatively, the construction of more specialized computer system to perform various operations, functions or steps of various methods described herein may be provided as desired or as appropriate without going beyond the scope of the present invention.

[0057] In addition, the present specification also at least implicitly discloses computer program(s) or software/functional module(s), in that it would be apparent to a person skilled in the art that various operations, functions or steps of various methods described herein may be put into effect by computer code. The computer program(s) is not intended to be limited to any particular programming language and implementation thereof, and it will be appreciated by a person skilled in the art that a variety of programming languages and coding thereof may be used to implement the computer program(s). Moreover, the computer program(s) is not intended to be limited to any particular control flow as there are a variety of programming languages which can use different control flows. It will be appreciated by a person skilled in the art that a computer program may be stored on any computer-readable storage medium (non- transitory computer-readable storage medium), such as but not limited to, a magnetic disk, an optical disk or a memory chip. For example, a computer program stored on a computer-readable storage medium may be loaded and executed on a computer system or device to implement various operations, functions or steps of various methods described herein according to various embodiments of the present invention.

[0058] Accordingly, in various embodiments, there is provided a computer program product, embodied in one or more computer-readable storage mediums (non-transitory computer-readable storage medium(s)), comprising instructions (e.g., the transition control signal receiving module 306, the mode transition controller 308, the monocopter mode controller 310 and/or the bicopter mode controller 312) executable by one or more computer processors to perform the method 200 of operating the single-wing rotorcraft 100, as described herein with reference to FIG. 2 according to various embodiments of the present invention. Accordingly, various computer programs or software modules described herein may be stored in a computer program product receivable by a system or device therein, such as the flight controller 150, for execution by at least one processor 304 of the flight controller 150 to perform various functions or operations described herein according to various embodiments of the present invention.

[0059] It will be appreciated by a person skilled in the art that various modules described herein (e.g., the transition control signal receiving module 306, the mode transition controller 308, the monocopter mode controller 310 and/or the bicopter mode controller 312) may be software module(s) realized by computer program(s) or set(s) of instructions executable by a computer processor to perform various functions or operations. Various modules described herein (e.g., the transition control signal receiving module 306, the mode transition controller 308, the monocopter mode controller 310 and/or the bicopter mode controller 312) may also be implemented as hardware module(s) being functional hardware unit(s) designed to perform various functions or operations. More particularly, in the hardware sense, a module is a functional hardware unit designed for use with other components or modules. For example, a module may be implemented using discrete electronic components, or it can form a portion of an entire electronic circuit such as an Application Specific Integrated Circuit (ASIC). Numerous other possibilities exist. It will also be appreciated by a person skilled in the art that a combination of hardware and software modules may be implemented. Furthermore, various operations, functions or steps of various methods described herein may be performed in parallel rather than sequentially as desired or as appropriate (e.g., as long as it does not render the method(s) inoperable or unsatisfactory for its intended purpose).

[0060] FIG. 4 depicts a schematic flow diagram of a method 400 of forming a single-wing rotorcraft 100 with multiple flight modes according to various embodiments the present invention. The method 400 comprises: providing or forming (at 402) a frame member 110; providing or forming (at 404) a wing member 120 coupled (e.g., rigidly/non-rotatably attached/affixed) to the frame member 110; providing or forming (at 406) a flap member 122 rotatably coupled to the frame member 110; providing or forming (at 408) a first thrust unit 130 rotatably coupled to the frame member 110 at a first portion 112 thereof and configured to generate a first thrust; providing or forming (at 410) a second thrust unit 132 rotatably coupled to the frame member 110 at a second portion 114 thereof and configured to generate a second thrust, the first and second portions 112, 114 being separated along the frame member 110 by a distance; providing or forming (at 412) a first actuator 140 configured to rotate the first thrust unit 130 about the frame member 110 with respect to (or relative to) the wing member 120; providing or forming (at 414) a second actuator 142 configured to rotate the second thrust unit 132 and the flap member 122 about the frame member 110 with respect to (or relative to) the wing member 120; and providing or forming (at 416) a flight controller 150 communicatively coupled to the first and second thrust units 130, 132 and the first and second actuators 140, 142 and configured to control, in response to a transition control signal received, the single-wing rotorcraft 100 to transition from one flight mode to another flight mode amongst the multiple flight modes during flight based on the first and second thrust units 130, 132 and the first and second actuators 140, 142. In this regard, the multiple flight modes comprising a monocopter mode and a bicopter mode.

[0061] In various embodiments, the method 400 is for forming the single-wing rotorcraft 100 as described hereinbefore with reference to FIG. 1, therefore, various steps or operations of the method 400 may correspond to forming, providing or configuring various components, modules or portions of the single-wing rotorcraft 100 as described herein according to various embodiments, and thus such corresponding steps or operations need not be described or repeated with respect to the method 400 for clarity and conciseness. In other words, various embodiments described herein in context of the single-wing rotorcraft 100 are analogously valid for the method 400 (e.g., for forming the single-wing rotorcraft 100 having various components, modules, portions and configurations as described hereinbefore according to various embodiments), and vice versa. It will also be appreciated by a person skilled in the art that the method 400 for forming the single-wing rotorcraft 100 is not limited to any particular order of operations/steps. For example, FIG. 4 does not indicate or limit any particular order of operations/steps in which the method 400 can be performed to form the single-wing rotorcraft 100. Furthermore, one or more operations/steps of the method 400 may be performed concurrently or integrally as desired or as appropriate without going beyond the scope of the present invention. For example, various components or parts of the single-wing rotorcraft 100 may be 3D printed components or parts, such as but not limited to, the frame member 110, the wing member 120, the flap member 122 and the housing member, and may be assembled together (e.g., coupled together), along with various other components or parts of the singlewing rotorcraft 100, to form the single-wing rotorcraft 100 as described herein according to various embodiments of the present invention. [0062] It will be appreciated by a person skilled in the art that the terminology used herein is for the purpose of describing various embodiments only and is not intended to be limiting of the present invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and/or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

[0063] Any reference to an element or a feature herein using a designation such as “first”, “second” and so forth does not limit the quantity or order of such elements or features, unless stated or the context requires otherwise. For example, such designations may be used herein as a convenient way of distinguishing between two or more elements or instances of an element. Thus, a reference to first and second elements does not necessarily mean that only two elements can be employed, or that the first element must precede the second element, unless stated or the context requires otherwise. In addition, a phrase referring to “at least one of’ a list of items refers to any single item therein or any combination of two or more items therein.

[0064] In order that the present invention may be readily understood and put into practical effect, various example embodiments of the present invention will be described hereinafter by way of examples only and not limitations. It will be appreciated by a person skilled in the art that the present invention may, however, be embodied in various different forms or configurations and should not be construed as limited to the example embodiments set forth hereinafter. Rather, these example embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the present invention to those skilled in the art.

[0065] Various example embodiments present design, modeling and control of a two-flight mode (or dual-mode) capable single-wing rotorcraft with mid-air transition ability. Conventional monocopters are nature-inspired, single-wing, rotating aerial vehicles that fly by spinning/rotating their entire body about its yaw axis. On the other hand, conventional bicopters are twin propeller-based aerial vehicles that may control their attitude by changing the direction of thrust forces from the two thrust units using two servos. In this regard, various example embodiments provide a single-wing rotorcraft (which may also be referred to as a single-wing aerial vehicle), which is capable of flying in both the monocopter and bicopter modes. To enhance its maneuverability while still being in the air, the single platform is configured to be capable of performing mid-air transition (i.e., during flight) from one flight mode to another flight mode. In various example embodiments, the control of the single-wing rotorcraft is developed by fusing various attributes of monocopter and bicopter, while allowing to maintain the natural shape of the monocopter (e.g., including the single-wing configuration) for flight. Considering forces and torques experienced by both flight modes (monocopter and bicopter modes), the dynamics of the single-wing rotorcraft are described, and a cascaded control strategy/technique is developed, according to various example embodiments of the present invention. Furthermore, in various example embodiments, a technique is provided to control an angular velocity of the single-wing rotorcraft in the monocopter mode. In addition, a blending and transition control method for controlling thrust units and actuators (e.g., servos) of the single-wing rotorcraft is developed for enhancing the transition of the single-wing rotorcraft between the two flight modes in an effective manner according to various example embodiments of the present invention. As an illustrative example only and without limitation, an example prototype of the single-wing rotorcraft will also be presented later below to demonstrate the flight of the single-wing rotorcraft in both flight modes, as well as transitions therebetween. As will also discussed later below, experimental results obtained based on the example prototype successfully verify designs/configurations of the single-wing rotorcraft according to various example embodiments, as well as control strategies/techniques implemented to control various states of the single-wing rotorcraft in both flight modes and transition therebetween.

[0066] Accordingly, to capitalize on different advantages of the monocopter and bicopter platforms, various example embodiments advantageously introduce a single-wing rotorcraft that is capable of flying in both monocopter and bicopter modes. As a result of providing both of these flight modes on a single platform in an effective manner, the single-wing rotorcraft can advantageously be adaptable in an operating environment and be employable in a wider range of practical applications, such as transiting to the monocopter mode when power/energy efficiency is desired and transitioning to the bicopter mode when flight stability (e.g., hovering with zero angular velocity) is desired. For example, the aerodynamic force produced by the wing of the single-wing rotorcraft and the rotating motion provides the monocopter mode with passive stability while hovering. In this regard, the ability to auto-rotate helps the monocopter mode to reduce/minimize its impact when hitting the ground in case of power failture (i.e., a softer landing in case of power failure). Moreover, recent research has also demonstrated that the rotating wing platform has superior power/energy efficiency compared to other types of platforms. For example, monocopters may be employed for various practical applications where the spinning nature of the monocopter platform can be utilized, such as passively scanning and mapping the surrounding environment. However, even though the conventional monocopter platform is based on a single wing, the physical footprint of the spinning monocopter is large enough to hinder its mobility whereby the conventional monocopter platform has a highly nonlinear dynamic nature. Moreover, cost-effective sensors available in the market may struggle to measure the state of the conventional monocopter as they may not be able to keep up with the rotational speed of the conventional monocopter platform.

[0067] On the other hand, the flight mode (bicopter mode) of a conventional bicopter is steady with zero angular velocity during hovering, which helps to achieve position and attitude control with easier or simpler control effort. For example, the steady nature of a conventional bicopter contributes to capabilities such as close inspections and steady mode video transmission. Additionally, the smaller footprint while hovering allows maneuvering through small or narrow spaces. However, conventional bicopters are less power/energy efficient than conventional monocopters, for example, since conventional bicopters are not configured to auto-rotate. In addition, conventional bicopters may bear a resemblance to a tailsitter, which may be particularly good for its efficiency in a forward-flight mode, however, owing to its forward velocity, the forward-flight mode may not be suitable for operations within a confined space. Furthermore, the tailsitter would simply crash during a fail-safe scenario, however, the monocopter mode can achieve a softer landing, comparatively.

[0068] Accordingly, the monocopter and bicopter modes have different advantages/benefits and disadvantages/limitations, and various example embodiments advantageously capitalize on the different advantages of the monocopter and bicopter platforms on a single platform (the single-wing rotorcraft) capable of flying in both monocopter and bicopter modes in an effective manner. For example, besides the capability of flying in two different flight modes, the single platform is also able to perform a transition from one flight mode to another flight mode without landing (i.e., during flight). In addition, to address the technical problem or difficulty of providing the two flight modes having completely different hovering styles (e.g., the monocopter mode rotates about the yaw axis when hovering and the bicopter mode is steady (zero angular velocity) when hovering) on a single platform, a blending and transition control method for controlling thrust units and actuators (e.g., servos) of the single-wing rotorcraft is developed for enhancing the transition of the single-wing rotorcraft between the two flight modes in an effective manner according to various example embodiments of the present invention. Therefore, for example, the single-wing rotorcraft may be a hybrid aerial vehicle operable to, for example, achieve a power-efficient flight in the monocopter mode and hover with zero angular velocity in the bicopter mode as desired. For simplicity, the monocopter mode and the bicopter mode may hereinafter be referred to as the M-mode and the B-mode, respectively.

[0069] Accordingly, various example embodiments provide:

• design and control of the single-wing rotorcraft with two different flight modes,

• experimental results demonstrating successful takeoff and position control in both flight modes, and

• experimental results demonstrating successful and effective transition between the two different flight modes during flight.

SINGLE-WING ROTORCRAFT AND DYNAMIC MODELING THEREOF

[0070] FIGs. 5 A to 5D depict schematic drawings of an example single-wing rotorcraft 500 (which may herein be referred to as an unmanned aerial vehicle (UAV)) with multiple flight modes (e.g., corresponding to the single-wing rotorcraft 100 as described herein according to various embodiments) at different views, according to various example embodiments of the present invention.

[0071] FIG. 5 A depicts a top view of the UAV 500 showing example locations and number of thrust units (Mi 530, M2 532) (e.g., each comprising a propeller and a motor for driving/rotating the propeller) (which may be referred to herein as the first and second thrust units 530, 532, respectively, e.g., corresponding to the first and second thrust units 130, 132 as described herein according to various embodiments) and actuators (Si 540, S2 542) (e.g., servos) (which may be referred to herein as the first and second actuators 540, 542, respectively, e.g., corresponding to the first and second actuators 140, 142 as described herein according to various embodiments), along with various dimensional parameters of the UAV 500 shown, according to various example embodiments of the present invention. In FIGs. 5A to 5C, the body frame B is defined in terms of x, y and z axes with respect to the center of gravity (CG) (denoted by the center of gravity symbol) of the UAV 500. Parameter Zi denotes the distance between the thrust force generated by the first thrust unit 530 and the CG in the -axis, parameter Li denote the distance between the thrust force generated by the second thrust unit 532 and the CG in the -axis, and parameter D denotes the distance between the thrust force generated by the first thrust unit 530 and the CG (and also denotes the distance between the thrust force generated by the second thrust unit 532 and the CG) in the z-axis. Parameters r _y and r _z denote the distances between the center of pressure (CP, the center of pressure is an imaginary point where the sum total of all the aerodynamic forces is located) and the CG in the y and z axes, respectively.

[0072] FIGs. 5B and 5C depict an isometric view of the UAV 500 in the M-mode and the B-mode, respectively, according to various example embodiments of the present invention, where B denotes the body frame attached to the CG, along various forces acting in the two modes shown. Parameters r _x , r _y , and r _z denote the torques generated in the body frame B in the x, y and z axes, respectively, and F _g denotes the gravitational force acting on the UAV 500, as illustrated in both FIGs. 5B and 5C. In FIG 5B, L and D denote the total lift and drag forces acting on the UAV 500 at the CP, respectively, and Qz denotes the angular velocity of the UAV 500 in the M-mode flight. 7i, Tz denote the thrust forces generated by the first and second thrust units 530, 532, respectively, 4i denote an angle (e.g., may be referred to herein as the first relative angle, the first rotation angle or the first servo angle) between the plane (y-z plane) of the wing member 520 and the direction of the thrust force generated by the first thrust unit 530 (which may be simply referred to herein as the angle between the first thrust unit 530 and the wing member 520), and A denote an angle (e.g., may be referred to herein as the second relative angle, the second rotation angle, the second flap angle or the second servo angle) between the plane (y-z plane) of the wing member 520 and the plane of the flap member 522 (as well as the direction of the thrust force generated by the second thrust unit 532) (e.g., as can be seen in FIG. 5C, the direction of the thrust force generated by the second thrust unit 532 is along (in) the plane of the flap member 522) (which may be simply referred to herein as the angle between the second thrust unit 532 (along with the flap member 522) and the wing member 520). In various example embodiments, both angles 4i and A are controllable/adjustable by the first and second actuators (e.g., servos) 540, 542, respectively. The rotation direction of propellers of the first and second thrust units 530, 532 and the UAV’s spin direction in the M-mode are also denoted with corresponding arrows, for example, FIG. 5B.

[0073] FIG. 5D depicts a cross-sectional view (viewing in a direction along the frame member 510 from the second thrust unit 532 to the first thrust unit 530) of the UAV 500, as well as showing the aerodynamic forces acting on the wing and the flap surfaces of the UAV 500, where d/. refers to lift force, dD refers to drag force, dV refers to normal force and dT refers to tangential force on each blade element (blade elements will be described further below). Furthermore, subscripts b and f denote the body and flap, respectively. [0074] In various example embodiments, the UAV 500 comprises: a frame member 510; a wing member 520 (which may simply be referred to as a wing) coupled (e.g., rigidly/non- rotatably attached/affixed) to the frame member 510; a flap member 522 (which may simply be referred to as a flap) rotatably coupled to the frame member 510 ; a first thrust unit 530 rotatably coupled to the frame member 510 at a first portion thereof and configured to generate a first thrust 7i; and a second thrust unit 532 rotatably coupled to the frame member 510 at a second portion thereof and configured to generate a second thrust Ti. In this regard, the first and second portions are separated along the frame member 510 by a distance (/.i + Li as shown in FIG. 5 A) (e.g., the distance may be configured as desired or as appropriate to facilitate flight in the B- mode). The UAV 500 further comprises a first actuator 540 configured to rotate the first thrust unit 530 about the frame member 510 with respect to (or relative to) the wing member 520; and a second actuator 542 configured to rotate the second thrust unit 532 and the flap member 522 about the frame member 510 with respect to (or relative to) the wing member 520. In addition, the UAV 500 comprises a flight controller (not shown in FIGs. 5A to 5D) communicatively coupled to the first and second thrust units 530, 532 and the first and second actuators 540, 542 and configured to control, in response to a transition control signal received, the UAV 500 to transition from one flight mode to another flight mode amongst the multiple flight modes (including the M-mode and the B-mode) during flight based on the first and second thrust units 530, 532 and the first and second actuators 540, 542.

[0075] In various example embodiments, the second actuator 542 is coupled to the second thrust unit 532 and the flap member 522 (e.g., via servo hom(s)) for rotating the second thrust unit 532 and flap member 522 about the frame member 510 with respect to (or relative to) the wing member 520.

[0076] In various example embodiments, the second thrust unit 532 has a fixed relationship with the flap member 522, and the second actuator 542 is configured to rotate the second thrust unit 532 and the flap member 522 together about the frame member 510 with respect to the wing member 520. That is, the second thrust unit 532 and the flap member 522 are arranged/configured to have a fixed relationship with respect to each other and the orientation of the second thrust unit 532 and the flap member 522 (collectively) about the frame member 510 is controllable/adjustable by the second actuator 542.

[0077] Accordingly, the first and second thrust units 530, 532 may each be rotatably coupled to the frame member 510. In particular, the first and second actuators 540, 542 may be respectively coupled to (e.g., via a servo horn) the first and second thrust units 530, 532 for respectively rotating the first and second thrust units 530, 532 about the frame member 510 with respect to the wing member 520. For example, the first and second thrust units 530, 532 may each be configured to generate a thrust 7i, Ti in a particular direction from the corresponding portion of the frame member 510 (e.g., thereby forming the corresponding rotation angle A or A) as controlled by the corresponding actuator 540/542. In various example embodiments, the first and second actuators 540, 542 are coupled (e.g., rigidly attached/affixed) to the wing member 520 at opposite edge portions of the wing member 520.

[0078] In various example embodiments, the UAV 500 further comprises a housing member 560 coupled (e.g., rigidly/non-rotatably attached/affixed) to the frame member 510. In various example embodiments, the flight controller is disposed on the housing member 560 (thereby housing the flight controller). Moreover, the housing member 560 is arranged between the first actuator 540 and the wing member 520, and the first actuator 540 is coupled to the wing member 520 via the housing member 560. That is, the first actuator 540 may be directly coupled to the housing member 560, and the housing member 560 may in turn be directly coupled to the wing member 520. Therefore, the first actuator 540 may be indirectly coupled to the wing member 520 via the housing member 560. For example, the first actuator 540 may be connected to the first thrust unit 530 through a linkage connecting a servo horn of the first actuator 540 and a mounting base of the first thrust unit 530. Similarly, the second actuator 542 may be connected to the second thrust unit 532 through a linkage connecting a servo horn of the second actuator 542 and a mounting base of the second thrust unit 532.

[0079] In various example embodiments, the second thrust unit 532 is configured to generate the second thrust Ti in a direction at least substantially perpendicular to the above- mentioned second portion of the frame member 510 and at least substantially opposite to a direction in which the flap member 522 extends from the above-mentioned second portion of the frame member 510 (e.g., configured to generate the second thrust Ti in the x-z plane). In various example embodiments, the first thrust unit 530 is configured to generate the first thrust Zi in a direction at least substantially perpendicular to the above-mentioned first portion of the frame member 510 (e.g., configured to generate the first thrust Ti in x-z plane).

[0080] In various example embodiments, as shown in FIGs. 5A to 5D, the first and second thrust units 530, 532 are arranged at a first side of the frame member 510, and the wing member 520 and the flap member 522 are arranged at a second side of the frame member 510. In this regard, the first and second sides of the frame member 510 are opposite sides. [0081] In various example embodiments, the frame member 510 is a rod. In this regard, the wing member 520 and the flap member 522 are arranged adjacent to each other (and nonoverlapping) along the rod 510 such that, in a non-actuated state, a plane (planar cross-section) of the wing member 520 and a plane (planar cross-section) of the flap member 522 are at least substantially along a same plane.

[0082] The dynamic modeling of the UAV 500 will now be described according to various example embodiments of the present invention. Let denote the right-handed inertial frame and denote the body frame attached to the Centre of Gravity (CG) of the UAV 500 such as shown in FIGs. 5B and 5C. The rotation angles about the X ³ , Y ³ and Z ³ axes of the inertial frame J are denoted by <p, 0, and X/J, respectively. Using the Newton- Euler formulation, the translational dynamics of the UAV 500 may be expressed as,

(Equation 1) where P ³ = [P _x , Py> PzV is the position vector in the inertial frame J , R _B represents the rotational transformation from the body frame B to the inertial frame J, F® = [F _x , Fy> ^zV is the force vector, and G = [0,0, g] ^T is the gravity vector.

[0083] Similarly, the attitude dynamics equation of the UAV 500 may be expressed as,

(Equation 2) where I ^s G ft ^3x3 is the inertia matrix, to® is the angular velocity in the body frame B, and T® ⁼ [ ^T x> ^T y> ^T Z] ^T is the torque vector.

[0084] In various example embodiments, the aerodynamic forces acting on the wing and flap surfaces (e.g., FIG. 5D) are modeled according to the Blade Element Theory (BET). Under BET, a surface is sliced span-wise into n blade elements, and the overall lift and drag contributions are obtained by summing up the individual contributions of the blade elements. Each blade element’s lift and drag contribution may be defined as,

(Equation 3) where C _t and C _d are the lift and drag coefficients respectively, p is the density of air, U is the relative air velocity encountered at the tip of the blade element (i.e., velocity of the oncoming air encountered by the tip of the blade element), c is the chord length of each blade element, and dr is the width of each blade element. d/. and d/J can be resolved into normal and tangential forces as,

(Equation 4) [0085] By integrating Equation (4), various example embodiments obtain the overall contribution of normal and tangential forces for both wing 520 and flap 522 which are at different angles of attack (6b and 9f, respectively) with respect to the inertial frame 7. In various example embodiments, the total normal ( ?) and tangential (Ti) forces from the wing 520 and the flap 522 are assumed to be acting on the Centre of Pressure (CP). These forces may be calculated as,

(Equation 5) where subscript t, b, and f refer to total, body and flap forces, respectively, and represents the rotational transformation from flap-frame to body-frame.

[0086] During the spinning/rotating motion of the UAV 500, a precession torque experienced (e.g., illustrated in FIG. 5B), which may be obtained by where, I _P and co _P is the moment of inertia and rotational speed of the propeller of the thrust unit. Considering the body frame axis definition, the first and third components (e.g., the x component and the z component , respectively) obtained for

^T prec ^w iH b ^e zero, ^an d therefore can be ignored. That is, ■ Using the Newton’s laws and the free body diagrams given in FIGs. 5 A to 5D, according to various example embodiments, the total force (F _x , F _y , F _z ) and moment ( _X , T _y , _Z ) equilibrium equations for the UAV 500 may be expressed as,

(Equation 6) T _Z = (Ti sin <?! L a + T ₂ sin 8 ₂ L ₂ - (N _t r _y )fl

(Equation 7) where /drag is drag force induced by the propeller of the thrust unit flying in its own wake and Tprec.2 (e.g., Tprec.y) is the second component (e.g., the component) of the precession torque r _prec . a, fl G [0, 1] are control parameters that can be varied to modify the dynamics of the overall system for a specific mode.

[0087] According to various example embodiments, considering the force (F _x , F _y , F _z ) and torque ( _X , T _y , _Z ) equilibrium of the UAV 500 (Equations (6) and (7)), and that the first thrust unit 530 and the first actuator 540 are not used for the M-mode, the body force (F _x , F _y , F _z ) and torque ( _X , T _y , _Z ) equations for the UAV 500 in the M-mode may be obtained by setting control parameters a = 0 and fl = 1 in Equations (6) and (7).

[0088] According to various example embodiments, a number of assumptions are made for simplification of the dynamics of the UAV 500 while flying in the B-mode, including:

1. the lift and drag generated by the wing 520 are considered to be negligible in steady state,

2. the reaction torques due to the actuators (servos) 540, 542 and thrust units 530, 532 are considered negligible as they are comparatively much smaller compared to the torque induced by the thrust in the body frame, and

3. the thrust force projected by the thrust units 530, 532 is considered to be only present in the x-z plane in the steady state. In this regard, although this thrust force will be proj ected in the j'-axis during the transient response but it will become zero as the roll angle of the UAV 500 converges to the commanded value by the flight controller. In various example embodiments, the thrust units 530, 532 are fixed to the frame member 510 in such a way that they cannot themselves produce any force in they axis (e.g., see FIG.

5 A). Therefore, if the thrust units 530, 532 are allowed to rotate about the frame member 510, the thrust force produced will be only in the x-z plane. However, for example, if the UAV 500 is rolled to the right side, the thrust force produced by the first thrust unit 530 will be more than that produced by the second thrust unit 532. In this case, the thrust force vector will be present in they-z plane. However, when the UAV 500 has rolled to the right according to the commanded value, the flight controller is configured to stabilize the UAV 500 again so that the UAV 500 does not roll anymore by balancing the thrust forces from the two thrust units 530, 532. Therefore, they component of the thrust force again becomes zero, and it can be assumed that the thrust force projected by the thrust units 530, 532 is only present in the x-z plane in the steady state.

[0089] Accordingly, in various example embodiments, considering the above assumptions, the body force (F _x , F _y , F _z ) and torque (r _x , T _y , T _Z ) equations for the UAV 500 in the B-mode may be obtained by setting a = 1 and fl = 0 in Equations (6) and (7). Therefore, in various example embodiments, the control of the UAV 500 is advantageously developed by fusing various attributes of monocopter and bicopter, while maintaining the natural shape of the monocopter (e.g., including the single-wing configuration) for flight. That is, a common set of body force (F _x , / , F _z ) and torque (r _x , T _y , T _Z ) equations for the UAV 500 for both the M-mode and the B-mode is advantageously provided according to various example embodiments of the present invention.

[0090] It will be appreciated by a person skilled in the art the UAV 500 is not limited to the example configuration/form (e.g., shape/size/configuration of the wing member 520, the flap member 522 and the frame member 510 and dimensional parameters of the UAV 500 such as those shown in FIG. 5A) as described herein and as shown in FIGs. 5A to 5D, and that the configuration/form of the UAV 500 may be modified or varied as desired or as appropriate without going beyond the scope of the present invention, as long as the UAV 500 is capable of operating in multiple different flight modes (including the monocopter and bicopter modes) on a single platform and comprises a flight controller communicatively coupled to first and second thrust units 530, 532 and first and second actuators 540, 542 and configured to control, in response to a transition control signal received, the UAV 500 to transition from one flight mode to another flight mode amongst the multiple flight modes during flight based on the first and second thrust units 530, 532 and the first and second actuators 540, 542, as described herein according to various example embodiments of the present invention.

FLIGHT CONTROL AND TRANSITION

[0091] FIG. 6 depicts a schematic block diagram of an example flight controller 550 (flight control architecture) of the UAV 500 according to various example embodiments of the present invention (e.g., corresponding to the flight controller 150 of the single-wing rotorcraft 100 as described herein according to various embodiments). The flight controller 550 may be configured to include three main sections/modules: (1) M-mode control, (2) B-mode control and (3) mode transition control. In particular, in various example embodiments, the flight controller 550 comprises: a M-mode controller 610 configured to control a flight of the UAV 550 in the M-mode; a B-mode controller 612 configured to control a flight of the UAV 550 in the B-mode; and a mode transition controller 608 communicatively coupled to the M-mode controller 610 and the B-mode controller 612 and configured to control, in response to a transition control signal 620 received, the first and second actuators 540, 542 and the first and second thrust units 530, 532 during a transition phase to transition the UAV 500 from one flight mode to another flight mode amongst the multiple flight modes during flight. In this regard, the transition control signal 620 received is to instruct the flight controller 550 to transition the UAV 500 from the M-mode to the B-mode or from the B-mode to the M-mode.

[0092] As shown in FIG. 6, in various example embodiments, the flight controller 550 is based on a cascaded control architecture/strategy, where the higher level controller controls the position of the UAV 500 in the three-axes (x, y, z axes). The flight controller 550 is configured to control both the position and the attitude of the UAV 500. In this regard, in various example embodiments, for the cascaded control architecture, a position controller (higher level or outer controller) is provided outside the attitude controller loop (lower level or inner controller). Accordingly, in various example embodiments, the lower level controller (attitude controller) may not be directly controlled by a user, and may be controlled via the higher level controller (position controller).

[0093] In various example embodiments, input switch(es) 624 (e.g., manual switch(es)) may be provided and configured to control flight input data (or signals) (e.g., desired attitude command/signal, desired altitude command/signal and desired rotational speed command/signal) to be fed from a remote controller (e.g., radio controller operated by a user) 626 or from a velocity controller 632, an altitude controller 634 and a rotational speed input 636 in a closed-loop control such as shown in FIG. 6. In other words, the input switch(es) 624 may be configured to selectively connect flight input data communication path(s) leading to the M-mode controller 610, the B-mode controller 612 and/or the mode transition controller 608 to flight input data communication path(s) configured to receive flight input data from the remote controller 626 or flight input data communication path(s) configured to receive flight input data from the velocity controller 632, the altitude controller 634 and/or the rotational speed input M-Mode Control

[0094] In various example embodiments, the M-mode controller 610 is configured to control a flight of the UAV 550 in the M-mode. In this regard, the M-mode controller 610 may comprise a cyclic controller 611 configured to generate a periodic signal (cyclic control signal) for controlling the thrust force generated by the second thrust unit 532 to steer the UAV 500 operating in the M-mode in a specific or desired direction, which may be referred to as a lower level controller for the M-mode. In various example embodiments, the cyclic control signal is configured to pulse the second thrust unit 532 at a particular/determined heading angle of the UAV 500 and with a particular/determined magnitude in each of a plurality of rotation cycles to steer the UAV 500 operating in the M-mode in a specific or desired direction. In various example embodiments, the cyclic control for the UAV 500 in the M-mode may be based on a square cyclic control strategy/technique such as previously described in Win et al.. “Achieving Efficient Controlled Flight with a Single Actuator”, 2020 IEEE/ASME International Conference on Advanced Intelligent Mechatronics (AIM), 2020, pages 1625-1631. As the square cyclic control technique is known in the art, it is not necessary to describe the square cyclic control technique in detail for conciseness. In general, the cyclic control technique may be implemented by controlling the roll and pitch of a rotating body (e.g., a helicopter blade or a rotorcraft such as a monocopter). Inputs to the cyclic controller 611 may include commanded values of roll/pitch (e.g., included in the desired attitude command/signal) and a parameter to scale the effectiveness of these commanded values, such as presented in Equation (8) below. The cyclic controller 611 may be configured to generate and output a sinusoidal control signal based on the inputs thereto. In various example embodiments, since the motors of the thrust units 530, 532 may not be able to actuate at the same rate as the rotational speed of the UAV 500, the sinusoidal control signal is converted or divided into a square cyclic control signal, such as presented in Equation (9) below.

[0095] For example, during flight in the M-mode, the UAV 500 constantly rotates in the Z- axis (i.e., the yaw axis of the UAV 500). In various example embodiments, the altitude error of the UAV 500 may be corrected based on the altitude controller 634 of which may be based on a PID control. In this regard, the cyclic controller 611 may receive a commanded value of altitude (e.g., included in the desired altitude command/signal) from the altitude controller 634 for altitude correction in the Z direction. The directional control of the UAV 500 correlates to the roll ( <p _c ) and pitch (ft) input commands (e.g., included in the desired attitude command/signal) for position correction in the X and Y directions. In various example embodiments, the direction control variable ip _c and the amplitude (Tamp) of the cyclic control signal may be computed as,

(Equation 8) where k _c is a constant to scale the effectiveness of roll and pitch input (actuation) commands. For example, as shown in FIG 6, the roll and pitch input commands (included in the desired attitude command/signal) either may be generated by the radio controller 626 as commanded by an operator/user or may be generated by the velocity controller 632 in the case of closed- loop control. In various example embodiments, the cyclic commanded thrust (cyclic control signal T _cyc ) for controlling a motor of a thrust unit to generate a thrust force includes both the altitude and the directional components for the altitude and directional controls and may be computed as, c ^yc ~ u _z - T _amp , otherwise

(Equation 9) where uz is the altitude correction, p is the current azimuth heading of the UAV 500 in the M- mode, xp ₀ is the offset value for angular correction induced due to gyroscopic precision and other effects, and e is the variable to control the duty cycle.

[0096] Accordingly, in various example embodiments, directional control in the M-mode flight may be implemented based on roll and pitch input commands included in the desired attitude command/signal. In general, if a rotating body (e.g., a helicopter blade) pitches down/up, the aerial vehicle (e.g., a helicopter) moves forward/backward. Furthermore, if the rotating body rolls left/right, the aerial vehicle moves left/right. The same or similar control principle may apply to a rotorcraft (e.g., a monocopter) as well. For example, in relation to the UAV 500 in the M-mode, to move the UAV 500 forward/backward, a pitch input command may be provided. Similarly, to move the UAV 500 left/right, a roll input command may be provided. In this regard, in various example embodiments, Equation (8) determines the direction control variable, which is a parameter used to control the direction in which the UAV 500 is to fly in the M-mode. Accordingly, Equation(8) maps the roll and pitch input commands (e.g., included in the desired attitude command/signal) to generate a cyclic control signal for controlling the thrust force generated by the second thrust unit 532 for directional control. The T _amp parameter in Equation (8) denotes the amplitude of the cyclic control signal, which basically corresponds to the effectiveness of the roll and pitch input commands. For example, as shown in FIG. 6, the roll and pitch input values ( _C and 0c in Equation (8) either may be obtained from the radio controller 626 or computed by the position and velocity controllers 630, 632 and included in (or constituting) the desired attitude command/ signal. Equation (9) defines the output command (square cyclic control signal) generated by the cyclic controller 611 for controlling the thrust force generated by the second thrust unit 532 to steer the UAV 500 operating in the M-mode. Accordingly, the cyclic control signal T _cyc is configured to pulse the second thrust unit 532 at a particular/determined heading angle of the UAV 500 (based on the direction control variable/i _c ) and with a particular/determined magnitude (based on the amplitude T _amp ) in each of a plurality of rotation cycles to steer the UAV 500 operating in the M-mode in a specific or desired direction.

[0097] For example, when flying manually (i.e., flight input data is obtained from the radio controller 626 being operated by an operator/user), the cyclic controller 611 obtains, as inputs thereto, the desired attitude command/signal (including roll and pitch input commands) and the desired altitude command/signal (including altitude input command) from the radio controller 626 (e.g., based on the roll, pitch and thrust sticks of the radio controller 626). On the other hand, when flying with position control (closed-loop control), the roll and pitch input commands may be computed by the position and velocity controllers 630, 632 and the altitude input command may be computed by the altitude controller 634. According to Equation (9), the cyclic controller 611 may be governed by a condition where the sine value of the current azimuth heading, direction control variable, and offset value for angular correction are computed to equate with the duty cycle variable. For example, the current azimuth heading may be obtained from a magnetometer onboard, and the direction control variable may be determined according to Equation (8). To offset the direction, a manual correction term for offset may be included if desired. In various example embodiments, the duty cycle may be adjusted based on a performance obtained from the magnetometer to achieve an equal share of roll and pitch value inputs.

[0098] Conventionally, a single actuator monocopter does not have control over the rate at which it is spinning/rotating. This rate of spin (i.e., the angular velocity) depends on the shape, size and weight distribution of the UAV. In contrast, according to various example embodiments, the flight controller 550 is further configured to be able to control the angular velocity of the UAV 500 in the M-mode for better efficiency, more control authority and to assist in the transition between different modes. In this regard, in various example embodiments, the M-mode controller 610 may further comprise a rotational speed controller 638 configured to control the second actuator 542 to control/adjust the angle h (e.g., may be referred to as the second flap or servo angle) of the flap 522 and the second thrust unit 532 with respect to the wing 520 for providing extra lift to control the rotational speed of the UAV 500 in the M-mode as well as reducing the effort on the motor of the second thrust unit 532. In various example embodiments, the rotational speed controller 638 may be configured to determine a second actuator control signal based on the desired rotational speed of the UAV 500 in the M-mode and output the second actuator control signal to the mode transition controller 608 for controlling the UAV 500 to achieve the desired rotational speed. In this regard, based on the second actuator control signal received, the mode transition controller 608 is configured to control/adjust the second flap (or servo) angle A and the thrust generated by the second thrust unit 532 to achieve the desired rotational speed of the UAV 500 in the M-mode. For example, by being able to control/adjust the rotation speed (angular velocity) of the UAV 500 in the M- mode, the rotational speed can advantageously be controlled/adjusted for various practical applications, such as to match with sensors (e.g., LIDAR) for various purposes.

[0099] Various example embodiments note that owing to the fast-spinning speed of the UAV 500 in the M-mode, the force components perpendicular to the rotating axis can be treated as zero over a rotation cycle in the inertial frame as they have a limited impact on the translational motion. In the hovering state, the collective force aligned with the rotating axis balances the gravity. Accordingly, various example embodiments determine the force and torque equilibrium for hovering using,

(Equation 10) where /?®(1, : ) refers to the first row of the rotation matrix R _B ' since the gravity is applied on the x-axis in the M-mode (e.g., see FIG. 5B). By solving Equation (10), various example embodiments obtain an equilibrium (a balance of the forces and torques to sustain a steady hovering flight in the M-mode) of thrust Ti, roll angle , pitch angle 0, as well as the rotating speed Qz. In particular, by controlling/adjusting the second servo angle di, the rotating speed Q _z of the UAV 500 can be controlled/adjusted. In various example embodiments, as described above, the second actuator control signal is determined by the rotational speed controller 638 and sent to the mode transition controller 608 for implementation. For example, using onboard sensors or position and attitude tracking system (such as Optitrack, etc.), the current rotational speed of the UAV 500 (corresponding to _X in Equation (10)) can be determined or obtained. Based on the desired rotational speed input/value, the rotational speed error value may thus be determined based on the current rotational speed and the desired rotational speed. The rotational speed error value may then be used in a proportional controller to determine the value of the second servo angle A (e.g., included in the second actuator control signal). In various example embodiments, to compensate for the loss/gain in altitude (A/i + due to a change in the second servo angle A, the mode transition controller 608 automatically adjusts the value of thrust force generated by the second thrust unit 532 to balance F _x .

[00100] Accordingly, in M-mode control, the mode transition controller 608 is configured to output a second thrust output command/signal to the second thrust unit 532 based on the cyclic control signal T _cyc (corresponding to the second thrust control signal produced based on the M-mode controller 610) for controlling the second thrust Ti generated by the second thrust unit 532 and output a second actuator output command/signal to the second actuator 542 based on the second actuator control signal determined by the rotational speed controller 638 for controlling/adjusting the second actuator 542 to achieve the desired servo angle A. In various example embodiments, as described above, the second thrust output command/signal output to the second thrust unit 532 may be produced further based on the second actuator control signal received from the rotational speed controller 638.

B-Mode Control

[00101] In various example embodiments, the B-mode controller 612 is configured to control a flight of the UAV 550 in the B-mode. In this regard, the B-mode controller 612 may comprise an attitude controller comprising an angle controller 614 (e.g., a higher-level quaternion-based controller) and an angular rate controller 616 (e.g., a lower-level angular rate controller). In various example embodiments, the inputs for the attitude controller may include the UAV quaternion and the desired attitude. For example, the quaternion-based controller may be based on the quaternion-based control disclosed in Brescianini et al., “Nonlinear quadrocopter attitude control”, Technical Report 9970340, ETH Zurich, 2013. In various example embodiments, the higher-level angle controller 614 for the attitude control may be configured to determine the desired angular rates vector Qd as follows,

(Equation 11) where CA is the attitude gain vector, and q _err = q ^-1 ■ q _d is the error quaternion. For example, the quaternion q may be obtained from the onboard Inertial Measurement Unit (IMU) or the Optitrack camera system (a position and attitude feedback system). In various example embodiments, by considering q = [q _w , q _x , q _y , q _z ] and the desired quaternion q _d = [q _Wd , q _Xd , q _yd , q _Zd ] , the error quaternion q _err may be determined as q _err = this regard, the directional components vector

[00102] In various example embodiments, the lower-level attitude control is the angular rate controller 616, which may be a PID control over the angular rate of the UAV 500 given by,

(Equation 12) where T _d = [z _xd , T _yd , T _zd \ is the desired moment vector, c _Pa , c _da and c _ia are the proportional, derivative, and integral gain vectors, and e _a is the angular rate error vector. In various example embodiments, the angular rate error vector e _a may be determined as e _a = are the desired angular rates for the

UAV 500 to fly in a stable manner determined using Equation (11) and Q. _x , Q. _y , Q. _z are the current angular rates of the UAV 500, such as obtained from an IMU.

[00103] In various example embodiments, for control allocations in the B-mode, the mode transition controller 608 is configured to generate first and second thrust control signals (corresponding to Ti and Ti, respectively) for controlling the first and second thrust units 530, 532, respectively, and first and second actuator control signals (corresponding to 4i and 32, respectively) for controlling the first and second actuators 540, 542, respectively, based on the desired moment vector (r _d ) output by the attitude controller (thus, based on the B-mode controller 612). In this regard, in various example embodiments, a relationship between the attitude controller output (rd) (along with Fzd) and the thrust and actuator control signals (corresponding to 7i, 2, 3i and A) is established. F _zd denotes the desired force in the z axis to keep the UAV 500 hovering in the B-mode, which for example, may either be obtained from the radio controller 626 or determined by the altitude controller 634. By way of an example only and without limitation, the thrust and actuator control signals (corresponding to Ti, T2, A and A) for the B-mode may be determined based on the moment vector (r _d ) and Equations (6) and (7) as follows,

(Equation 13 d) [00104] Accordingly, in various example embodiments, in B-mode control, the mode transition controller 608 is configured to: output first and second thrust output commands/signals (corresponding to Ti and Ti) for controlling the thrust forces generated by the first and second thrust unit 530, 532, respectively, and output first and second actuator output commands/signals (corresponding to <i and A) for controlling the first and second actuators 540, 542 to achieve first and second rotation (or servo) angles, respectively, based on the first and second thrust control signals and the first and second actuator control signals produced based on the B-mode controller 612 (i.e., the thrust and actuator control signals produced based on the desired moment vector produced by the B-mode controller 612).

Blended Transition Control

[00105] In various example embodiments, the mode transition controller 608 is communicatively coupled to the M-mode controller 610 and the B-mode controller 612 and configured to control, in response to the transition control signal 620 received (e.g., from the remote controller 626), the first and second actuators 540, 542 and the first and second thrust units 530, 532 during a transition phase to transition the UAV 500 between the M-mode and the B-mode amongst the multiple flight modes during flight. In various example embodiments, the transition control may be based on the concept of providing the best or optimal conditions for the subsequent flight mode to take over while maintaining the stability and control of the UAV 500 in the current flight mode. A simple approach for transitioning between the M-mode and the B-mode may be to simply turn on the M-mode controller 610 and turn off the B-mode controller 612 if transitioning from the B-mode to the M-mode, and simply turn off the B-mode controller 612 and turn off the M-mode controller 610 if transitioning from the M-mode to the B mode (i.e., a simple on-off method). However, various example embodiments note that such a simple approach for transitioning between the M-mode and the B-mode is not effective and may fail. To address this technical problem, upon receiving a transition control signal 620, the mode transition controller 608 is configured to control the first and second actuators 540, 542 and the first and second thrust units 530, 532 in the manner as will be described below according to various example embodiments to advantageously enhance the transition between the M- mode and the B-mode in an effective manner. In this regard, the mode transition controller 608 may employ a blending strategy for handing over control between the M-mode controller 610 and the B-mode controller 612 to effectively handle the two different types of flight modes based on two different attitude controllers.

[00106] In various example embodiments, the mode transition controller 608 is configured to, in response to the transition control signal 620 received being to instruct the flight controller 550 to transition the UAV 500 from the M-mode to the B-mode: control, during a first stage (or an initial stage) of the transition phase, the first actuator 540 to rotate, in a clockwise direction, the first thrust unit 530 about the frame member 510 with respect to (or relative to) the wing member 520 and the second actuator 532 to rotate, in the clockwise direction, the second thrust unit 532 and the flap member 522 about the frame member 510 with respect to (or relative to) the wing member 520 so as to increase a relative angle in the clockwise direction from a plane of the wing member 520 to a direction of the first thrust generated by the first thrust unit 530 (i.e., the relative angle in the clockwise direction between the plane of the wing member 520 and the direction of the first thrust) and to increase a relative angle in the clockwise direction from the plane of the wing member 520 to a plane of the flap member 522 and a direction of the second thrust generated by the second thrust unit 532 (i.e., the relative angle in the clockwise direction between the plane of the wing member 520 and the plane of the flap member 522 (as well as the direction of the second thrust) (in this regard, the direction of the second thrust is along (in) the plane of the flap member 522)) for increasing a pitch of (pitching up) the first and second thrust units 530, 532 and the flap member 522 so as to stall the wing member 520 (e.g., pitching up the UAV 500 decreases its rotational speed). In this regard, the clockwise direction is when viewed in a direction along the frame member 510 from the first thrust unit 530 to the second thrust unit 532. In various embodiments, the mode transition controller 608 is further configured to, in response to the transition control signal received being to instruct the flight controller 550 to transition the UAV 500 from the M-mode to the B-mode, control, during the first stage of the transition phase, the first thrust unit 530 to increase the first thrust generated by the first thrust unit 530 and the second thrust unit 532 to decrease the second thrust generated by the second thrust unit 532.

[00107] In various example embodiments, the mode transition controller 608 is further configured to, in response to the transition control signal 620 received being to instruct the flight controller 550 to transition the UAV 500 from the M-mode to the B-mode, control the first and second thrust units 530, 532 during the transition phase based on a first function configured to phase out a second thrust control signal produced based on the M-mode controller 610 for controlling the second thrust unit 532 and to phase in a first thrust control signal and a second thrust control signal produced based on the B-mode controller 612 for controlling the first and second thrust units 530, 532, respectively. In various example embodiments, the first function is a sigmoid function.

[00108] In various example embodiments, the mode transition controller 608 is further configured to, in response to the transition control signal 620 received being to instruct the flight controller 550 to transition the UAV 500 from the M-mode to the B-mode, control the first and second actuators 540, 542 during the transition phase based on the first function configured to further phase out a second actuator control signal produced based on the M-mode controller 610 for controlling the second actuator 542 and to phase in a first actuator control signal and a second actuator control signal produced based on the B-mode controller 612 for controlling the first and second actuators 540, 542, respectively. In various example embodiments, after phasing out the second thrust control signal and the second actuator control signal produced based on the M-mode controller 610, the mode transition controller 608 is configured to control: the first and second actuators 540, 542 based on the first and second actuator control signals produced based on the B-mode controller 612 for controlling the first and second actuators 540, 542, respectively; and the first and second thrust units 530, 532 based on the first and second thrust control signals produced based on the B-mode controller 612 for controlling the first and second thrust units 530, 532, respectively, thereby completing the transition of the UAV 500 from the M-mode to the B-mode.

[00109] Accordingly, in various example embodiments, when transitioning the UAV 500 from the M-mode to the B-mode, the mode transition controller 608 does not simply switch off the M-mode and switch on the B-mode, but controls the first and second actuators 540, 542 and the first and second thrust units 530, 532 in the manner as described herein according to various example embodiments to advantageously enhance the transition from the M-mode to the B- mode in an effective manner. For illustration purposes by way of examples only and without limitation, experimental values for the first and second thrust output commands/ signals and the first and second actuator output commands/signals output from the mode transition controller 608 for the first thrust unit 530, the second thrust unit 532, the first actuator 540 and the second actuator 542, respectively (referred to as ‘Motorl’, ‘Motor2’, ‘Servol’ and ‘Servo2’, respectively, in FIG. 17 A) during the B-mode and the M-mode, as well as during the transition from the B-mode to the M-mode, are shown in FIG. 17 A.

[00110] In various example embodiments, the mode transition controller 608 is configured to, in response to the transition control signal 620 received being to instruct the flight controller 550 to transition the UAV 500 from the B-mode to the M-mode: control, during a first stage (or initial stage) of the transition phase, the first actuator 540 to rotate, in an anti-clockwise direction, the first thrust unit 530 about the frame member 510 with respect to (or relative to) the wing member 520 and the second actuator 542 to rotate, in the anti-clockwise direction, the second thrust unit 532 and the flap member 522 about the frame member 510 with respect to (or relative to) the wing member 520 so as to increase a relative angle in the anti-clockwise direction from a plane of the wing member 520 to a direction of the first thrust generated by the first thrust unit 530 (i.e., the relative angle in the anti-clockwise direction between the plane of the wing member 520 and the direction of the first thrust) and to increase a relative angle in the anti -clockwise direction from the plane of the wing member 520 to a plane of the flap member 522 and a direction of the second thrust generated by the second thrust unit 532 (i.e., the relative angle in the anti-clockwise direction between the plane of the wing member 520 and the plane of the flap member 522 (as well as the direction of the second thrust) (in this regard, the direction of the second thrust is along (in) the plane of the flap member 522)) for decreasing a pitch of (pitching down) the first and second thrust units 530, 532 and the flap member 522. In this regard, the anti-clockwise direction is when viewed in a direction along the frame member 510 from the first thrust unit 530 to the second thrust unit 532. In various embodiments, the mode transition controller 608 is further configured to control, in response to the transition control signal received being to instruct the flight controller 550 to transition the UAV 500 from the B-mode to the M-mode, control, during the first stage of the transition phase, the first thrust unit 530 to decrease the first thrust generated by the first thrust unit 530 and the second thrust unit 532 to increase the second thrust generated by the second thrust unit 532 (e.g., which has been found to induce rotational motion in the anti -clockwise direction for transitioning to the M-mode). [00111] In various example embodiments, the mode transition controller 608 is further configured to, in response to the transition control signal 620 received being to instruct the flight controller 550 to transition the UAV 500 from the B-mode to the M-mode, control the first and second thrust units 530, 532 during the transition phase based on a second function configured to phase out a first thrust control signal and a second thrust control signal produced based on the B-mode controller 612 for controlling the first and second thrust units 530, 532, respectively, and to phase in a second thrust control signal produced based on the M-mode controller 610 for controlling the second thrust unit 532. In various example embodiments, the second function is a sigmoid function.

[00112] In various example embodiments, the mode transition controller 608 is further configured to, in response to the transition control signal 620 received being to instruct the flight controller 550 to transition the UAV 500 from the B-mode to the M-mode, control the first and second actuators 540, 542 during the transition phase based on the second function configured to further phase out a first actuator control signal and a second actuator control signal produced based on the B-mode controller 612 for controlling the first and second actuators 540, 542, respectively, and to phase in a second actuator control signal produced based on the M-mode controller 610 for controlling the second actuator 542. In various example embodiments, after phasing out the first and second thrust control signals and the first and second actuator control signals produced based on the B-mode controller 612, the mode transition controller 608 is configured to control: the second actuator 542 based on the second actuator control signal produced based on the M-mode controller 610 for controlling the second actuator 542; and the second thrust unit 532 based on the second thrust control signal produced based on the M-mode controller 610 for controlling the second thrust unit 532, thereby completing the transition of the UAV 500 from the B-mode to the M-mode.

[00113] Accordingly, in various example embodiments, when transitioning the UAV 500 from the B-mode to the M-mode, the mode transition controller 608 does not simply switch off the B-mode and switch on the M-mode, but controls the first and second actuators 540, 542 and the first and second thrust units 530, 532 in the manner as described herein according to various embodiments to advantageously enhance the transition from the B-mode to the M-mode in an effective manner. For illustration purposes by way of examples only and without limitation, experimental values for the first and second thrust output commands/signals and the first and second actuator output commands/signals output from the mode transition controller 608 for the first thrust unit 530, the second thrust unit 532, the first actuator 540 and the second actuator 542, respectively (referred to as ‘Motorl’, ‘Motor2’, ‘Servol’ and ‘Servo2’, respectively, in FIG. 17B) during the M-mode and the B-mode, as well as during the transition from the M- mode to the B-mode, are shown in FIG. 17B.

[00114] Accordingly, in various example embodiments, the transition technique/strategy developed for the UAV 500 may be heuristic-based to utilize the natural characteristics/properties of the flight modes and the attitude controllers implemented. As described hereinbefore, in various example embodiments, the mode transition controller 608 may include a phase-in phase-out control of the two flight modes based on a sigmoid function, preceded by a blending control, which involves a series of relative movements between the wing 520 and the flap 522 to orientate the UAV 500 and initiate the corresponding mode controller for the mode to transition to. FIG. 7 depicts plots of example thrust and actuator output commands/signals output from the mode transition controller 608 for the transition of the UAV 500 (switching of controls) (1) from the B-mode to the M-mode and (2) from the M- mode to the B-mode, to illustrate the initialization of blending using the thrust units 530, 532 and the thrust units (or servos) 540, 542 and the switching of the monocopter/bicopter mode controller 610, 612. In this regard, the blending control refers to the blending of the M-mode and B-mode controllers 610, 612, and more particularly, the blending of the thrust and actuator control signals produced based on the M-mode and B-mode controllers 610, 612, such as the thrust and actuator control signals produced according to Equations (9) and (13a) to (13d), for producing thrust and actuator output commands/signals for controlling the first and second thrust units 530, 532 and the first and second actuator units 540, 542, Accordingly, FIG. 7 provides an illustrative example of how the thrust and actuator output commands/signals may change for the transition of the UAV 500 from the B-mode to the M-mode and from the M- mode to the B-mode, which show example ideal/model values but not real/actual values. Accordingly, the transition is based on a gradual phase-in/phase-out of thrust and actuator control signals produced by the M-mode and B-mode controllers 610, 612. For example, once the flight controller 550 (or more specifically, the mode transition controller 608) receives a transition control signal (command for initializing a flight mode transition), the mode transition controller 608 may initiate the above-mentioned blending of the thrust and actuator control signals produced based on the M-mode and B-mode controllers 610, 612, such as the thrust and actuator control signals produced according to Equations (9) and (13a) to (13d). In FIG. 7, the transition phase for the blending and transition of controls corresponds to the zone from time unit 2 to 6. In FIG. 7, the servo angles are normalized from -1 to 1, control = 0 means no control and control = 1 means full control, and the thrust value is normalized from 0 to 100. In FIG 7 (and similarly in FIG. 8 described later below), the example thrust output commands/signals are referred to as ‘ Motor 1’ for the first thrust unit 530 and ‘Motor2’ for the second thrust unit 532, and the example actuator output commands/signals are referred to as ‘Servol’ for the first actuator 540 and ‘Servo2’ for the second actuator 542.

[00115] In various example embodiments, by way of example only and without limitation, the sigmoid function used for controlling switching output sw _c may be given by,

(Equation 14) where t is the time, and b and r are parameters used to define the offset and slope which may be changed as appropriate to obtain the desired results. The output of the sigmoid function may serve as a switching parameter sw _c whereby its value can be modified with the input parameters, namely, t, b, and r. For example, manipulating/modifying these input parameters can help in selecting/setting an appropriate delay and rate of change of sw _c as desired for performing the above-mentioned blending of the thrust and actuator control signals produced based on the M- mode and B-mode controllers 610, 612. For example, the thrust and actuator control signals for the M-mode may be produced based on the M-mode controller 610 (e.g., the thrust control signals may be produed according to Equation (9)) and the thrust and actuator control signals for the B-mode may be produced based on the B-mode controller 612 (e.g., according to Equations (13a) to (13b)). By way of an example and without limitation, in the case of transitioning from the M-mode to the B-mode, the second thrust control signal produced based on the M-mode controller 610 for controlling the second thrust unit 532 may be phased out and the first and second thrust control signals (7i _B-mode , T _2B-mode ) produced based on the B-mode controller 612 for controlling the first and second thrust units 530, 532 may be phased in according to an example thrust phasing equation: T _iM-mode + (Tt _B-mode ~ ^iM-mode) ^{x w} h ^ere ‘ z’ denotes the particular thrust unit (e.g., ‘ 1’ for the first thrust unit 530 and ‘2’ for the second thrust unit 532). In addition, the second actuator control signal ^2 _M-mode ) produced based on the M-mode controller 610 for controlling the second actuator unit 542 may be phased out and the first and second actuator control signals (<5 _1B-mode , ^2 _B-mode ) produced based on the B-mode controller 612 for controlling the first and second actuators 540, 542 may be phased in according to an example actuator phasing equation where ‘z’ denotes the particular actuator (e.g., ‘ 1’ for the first actuator 540 and ‘2’ for the second actuator 542). It will be appreciated by a person skilled in the art that the present invention is not limited to the above example thrust and actuator phasing equations, and thrust and actuator phasing equations may be configured or implemented in any form as desired or as appropriate as long as the thrust and actuator phasing equations can function (or is operable) to phase in / phase out the thrust and actuator control signals produced based on the M-mode controller 610 / B-mode controller 612 during the transition phase as described herein according to various example embodiments of the present invention. For example, the actuators 540, 542 and the thrust units 530, 532 may have different input ranges (e.g., an angle value between 0 and 180 degrees for the actuators 540, 542 and a PWM (pulse width modulation) value between 1000 and 2000 for the thrust units 530, 532). Based on these input values and the operation ranges of the thrust units 530, 532 and the actuators 540, 542 during the B-mode and the M-mode, different thrust and actuator phasing equations may be provided (i.e., thrust phasing equation and actuator phasing equation are in different forms, e.g., as described above) for controlling the phasing of the thrust and actuator control signals. For example, for the thrust units 530, 532, the phasing of thrust control signals may be performed from one flight mode to another flight mode while controlling the altitude. In this regard, the actuators 540, 542 also have the responsibility to change the attitude of the UAV 500 (e.g., in transition from the M-mode to the B-mode, pitching up the UAV 500; and in transition from the B-mode to the M-mode, pitching down the UAV 500).

[00116] Accordingly, in various example embodiments for the transition of the UAV 500 from the M-mode to the B-mode, after phasing out the second thrust control signal and the second actuator control signal produced based on the M-mode controller 610, the mode transition controller 608 may be configured to control: the first and second actuators 540, 542 based on the first and second actuator control signals produced based on the B-mode controller 612 for controlling the first and second actuators 540, 542, respectively; and the first and second thrust units 530, 532 based on the first and second thrust control signals produced based on the B-mode controller 612 for controlling the first and second thrust units 530, 532, respectively, thereby completing the transition of the UAV 500 from the M-mode to the B-mode. Similarly, in various example embodiments for the transition of the UAV 500 from the B-mode to the M- mode, after phasing out the first and second thrust control signals and the first and second actuator control signals produced based on the B-mode controller 612, the mode transition controller 608 may be configured to control: the second actuator 542 based on a second actuator control signal produced based on the M-mode controller 610 for controlling the second actuator 542; and the second thrust unit 532 based on the second thrust control signal produced based on the M-mode controller 610 for controlling the second thrust unit 532, thereby completing the transition of the UAV 500 from the B-mode to the M-mode

[00117] FIG. 8 illustrate example transitions of the UAV 500 between the B-mode to the M- mode (from the B-mode to the M-mode and vice versa) according to various example embodiments of the present invention, along with various stages encountered during the transitions. In various example embodiments, to transition from the B-mode to the M-mode, the natural stability of the UAV 500 in the M-mode was utilized. In this regard, the natural characteristic of the UAV 500 in the M-mode spinning/rotating naturally on its axis when falling through the air was utilized to initiate the transition. In various example embodiments, to transition from the M-mode to the B-mode, the stalling of the wing 520 was triggered to subside the rotation rate as quickly as possible and to pitch up the UAV 500 to orientate the UAV for the B-mode controller 612 to take over. In particular, FIG. 8 depicts an example transition cycle showing changes in orientation of the UAV 500 when transitioning between the M-mode and B-mode. The example transitioning from the B-mode to the M-mode follows the upper dotted arrow from left to right. At stage B-l, the UAV 500 pitches down aggressively, while simultaneously increasing and decreasing the second thrust unit 532 and the first thrust unit 530, respectively. Due to the uneven thrust, at stage B-2, the UAV 500 starts to gain rotational velocity. As the velocity increases, the M-mode controller 610 takes over majority control (and gradually complete control) in stage B-3 and the crossover point (e.g., as illustrated in FIG. 7 at t = 5 seconds) at stage B-3 may be referred to as the switching point from the B- mode to M-mode. The example transitioning from the M-mode to the B-mode follows the lower dotted arrow. At stage M-l, the UAV 500 stalls the flap 522 to increase the pitch and decrease the rotational speed, while simultaneously increasing and decreasing the first thrust unit 530 and the second thrust unit 532, respectively. In this regard, the stalling of wing 520 and balance of thrust of the thrust units 530, 532 reduce the rotational speed further in stage M-2, while the actuators (servos) 540, 542 start to align to desired values. At stage M-3, the B-mode controller 612 takes over majority control (and gradually complete control) and the crossover point (e.g., as illustrated in FIG. 7 at t = 5 seconds) at stage M-3 may be referred to as the switching point from M-mode to B-mode.

[00118] In various example embodiments, the transition from the B-mode to the M-mode starts with an aggressive pitch maneuver and simultaneous controlled reduction of the thrust generated by the first thrust unit 530. The thrust of the first thrust unit 530 is controlled to continue reducing as orientation changes to facilitate the transition to the M-mode. When the M-mode controller 610 takes over complete control, the first actuator 540 and the first thrust unit 530 may be disabled to minimise power consumption (e.g., conserve onboard battery). In various example embodiments, to transition from the M-mode to the B-mode, the UAV 500 utilizes the second actuator 542 to intentionally stall the wing 520 by reducing the rotational speed and gaining high pitch, followed by initiation of the first actuator 540 and the first thrust unit 530 and finally passing the control of the UAV 500 based on the outputs of the B-mode controller 612.

[00119] In various example embodiments, to enhance the robustness and reliability of the transition of the UAV 500 between the M-mode and the B-mode, an optimal transition sequence is designed or obtained by minimizing a cost function for better control during the transition.

EXPERIMENTAL RESULTS

[00120] FIG. 9 depicts a front or top view and a back or bottom view of an example physical prototype of the UAV 900 according to various example embodiments of the present invention (e.g., corresponding to the single-wing rotorcraft 100 as described hereinbefore according to various embodiments and the UAV 500 as described hereinbefore according to various example embodiments). For example, for experimental verification of the corresponding single-wing rotorcraft 100 and the corresponding UAV 500, various experiments were performed on the UAV 900 as will be described later below according to various example embodiments of the present invention.

[00121] As shown in FIG. 9, the UAV 900 comprises a carbon fibre rod 910 (e.g., corresponding to the frame member 110/510 as described hereinbefore), 3D printed structures for holding the two servos 940, 942 (e.g., corresponding to the two actuators 140/540, 142/542 as described hereinbefore), two thrust units 930, 932 (e.g., corresponding to the two thrust units 130/530, 132/532 as described hereinbefore), and landing gears 960 on each side, and a wing 920 (e.g., corresponding to the wing member 120/520) and flap 922 (e.g., corresponding to the flap member 122/522) cut from Balsa wood. Two EMax 30 A ESCs (electronic speed controllers) are provided to drive the twin TMotor 4500 KV brushless motors of the two thrust units 930, 932, respectively. For each of the two thrust units 930, 932, the motor is attached to a 3 -inch propeller, capable of generating a maximum of 100 g of thrust, which leaves sufficient overhead for controlling the UAV 900, which weighs about 152 g in total. Using a standard 3S 300 mAh Li-Po battery 962, the UAV 900 has an endurance of approximately 2.8 ± 0.2 mins while hovering in the B-mode and 3.2 ± 0.2 mins while hovering in the M-mode. An ESP32 micro-controller (flight controller) 950 (e.g., corresponding ot the flight controller 150/550 as described hereinbefore) was used onboard, which is connected through a receiver to the transmitter for receiving a manual signal as well as through Wi-Fi to the ground station. FIG. 10 shows a Table (Table 2) presenting various dimensional and gain parameters associated with the UAV 900, along with their example numerical values, according to various example embodiments of the present invention.

[00122] For illustration purposes only, FIGs. 11A and 11B show pictures of the UAV 900 during experimental flight in the M-mode and the B-mode (flying through a narrow opening), respectively, according to various example embodiments of the present invention.

[00123] In various example embodiments, testing of the UAV 900 was performed to verify the following objectives: (1) both the M-mode and the B-mode are fully operable with control over position and attitude, and (2) in-flight transition can be performed effectively from one flight mode to flight another. In various experiments, along with the sensors onboard, an OptiTrack system was used to provide position and orientation data for closed-loop control (e.g., as illustrated in FIG. 6).

[00124] FIG. 12 show plots comparing the power consumption of the UAV 900 when hovering in the M-mode and the B-mode, according to various example embodiments of the present invention. It was observed that during the B-mode, which utilizes both thrust units 930, 932 and both actuators (servos) 940, 942, the current drawn and hence the power consumed is more compared to the M-mode. On average, hovering flight in the B-mode consumed approximately 50.38 W, compared to 40.45 W consumed by the M-mode, making the M-mode 21.86% more power/energy efficient.

[00125] FIG. 13 shows plots of the Euler angles of the UAV 900 during the M-mode and B- mode flights, according to various example embodiments of the present invention. For the M- mode flight, the roll and pitch of the UAV 900 were varying between ±0. 1 rad, indicating the effort to hold the position using the cyclic control implemented (e.g., corresponding to the B- mode controller 310/610 as described hereinbefore). FIG. 13 also show plots of the angular velocity z for the M-mode flight, which is controlled by the rotational speed controller (e.g., corresponding to the rotational speed controller 638 as described hereinbefore). On the other hand, the roll, pitch, and yaw values for the B-mode flight fluctuate only between ±0.05 rad, depicting more stability during hovering compared to the M-mode flight. Position Tracking

[00126] Various experiments were conducted to fly the UAV 900 in the M-mode and the flmode using the flight controller 950 according to various example embodiments of the present invention. For example, the UAV 900 was commanded to fly towards waypoints forming a square pattern and to fly in a circular path to follow a trajectory. FIGs. 14A and 15A depict plots of the desired position (Xd, Yd, Zd) and the actual position (X, Y, Z) of the UAV 900, along with the thrust and actuator output commands/ signals (for the second thrust unit 932 and the second actuator 942, referred to as ‘Motor2’ and ‘Servo2’, respectively, in FIGs. 14A and 15 A), while following the waypoints forming the square pattern (i.e., square shaped waypoint tracking) (FIG. 14 A) and while flying in the circular path to track the trajectory (FIG. 15 A), respectively, for the M-mode flight. From FIGs. 14A and 15 A, it can be observed that altitude control is very responsive and stable, due to the direct control of the second thrust unit 932 over the Z-axis. The position control, however, is hindered by the nonlinear nature of the UAV platform. A slower response is observed because of indirect control and due to the gyroscopic nature of the UAV 900. In various example embodiments, to enhance the response speed, a nonlinear controller may be implemented.

[00127] FIGs. 14B and 15B depict plots of the desired position (Xd, Yd, Zd) and the actual position (X, Y, Z) of the UAV 900, along with the thrust and actuator output commands/signals (for the first thrust unit 930, the second thrust unit 932, the first actuator 940 and the second actuator 942, referred to as ‘Motorl ’, ‘Motor2’, ‘ServoT and ‘Servo2’, respectively, in FIGs. 14B and 15B) while following the waypoints forming the square pattern (FIG. 14B) and while flying in the circular path to track the trajectory (FIG. 15B), respectively, for the B-mode flight. From FIGs. 14B and 15B, it can be observed that the B-mode has better control over the position compared to the M-mode. For example, a comparison of FIG. 14A and 14B shows that the flmode can reach the waypoints and hold position better compared to the M-mode. Likewise, FIG. 15B shows that the transient motion of the B-mode is better compared to the M-mode as shown in FIG. 15A (in particular, between 20 and 40 seconds, the roughness of the M-mode motion can be observed). Although, the B-mode portrayed some delay in response in the X- axis, this is due to the aerodynamic force affecting the wing and flap surfaces while moving in that direction. This is a trade-off effect that can be reduced by optimizing the shape of the wing and flap to obtain minimum surface area facing the wind while providing the best lift while rotating in the M-mode. [00128] The Root Mean Square (RMS) values obtained for the square shaped waypoint tracking for the M-mode flight and the B-mode flight are 0.214 and 0.194, respectively. The Root Mean Square (RMS) values obtained for the circular trajectory tracking for the M-mode flight and the B-mode flight are 0.176 and 0.134, respectively. Accordingly, comparing the RMS values for the position tracking while following square shape waypoints for the M-mode and the B-mode, the B-mode performed 10.31% better, whereas for the circular trajectory (see FIGs. 14B and 15B), this performance was 31.34% better. Overall, the constant spinning nature of the M-mode affected the translational motion and hovering of the UAV 900, whereas the steady nature of the B-mode helped it achieve better translational motion as well as position holding after reaching the waypoints.

Transition Between the M-mode and the B-mode

[00129] Due to the completely different nature of the flight style of the M-mode and the B- mode, in various example embodiments of the present invention, the blended transition technique is advantageously employed to facilitate the UAV 900 to transition from one flight mode to another flight mode during flight in an effective manner. In various experiments conducted, the transitions of the UAV 900 between the two flight modes were tested and observed. During the transition from the B-mode to the M-mode, it was found that the UAV 900 can reliably switch, although losing altitude since the M-mode relies on the lift produced by the wing 920 and the spinning nature of the UAV 900 to gain altitude. In the transition from the M-mode to the B-mode, the stalling of the UAV 900 was found to be effective in reducing the rotational speed, although the UAV 900 may take some time to recover after entering the B-mode. According to various example embodiments, an iterative approach based on the results obtained was employed to tune the switching function parameters defined in the Equation (14) described hereinbefore to further enhance the transition of the UAV 900 between the two flight modes.

[00130] Various example embodiments note several factors weigh-in for the success or failure of a transition. The natural autorotation of the UAV 900 in the M-mode may require a certain distance to start, which is proportional to its weight and size. Therefore, the rate at which the motors of the thrust units 930, 932 start assisting the rotation to enter the M-mode may impact the success or failure of the transition from the B-mode to the M-mode. On the other hand, once the wing 920 is stalled, the pitch angle can start to either decrease or increase. The first scenario may be favourable, however, beyond a certain angle, the latter scenario may make the transition unstable. Furthermore, various example embodiments note as the rotational speed is decreased to enter the B-mode, the UAV 900 has a tendency to fall inwards due to the gravity and the location of the center of gravity. Both these factors can affect the success or failure of transition from the M-mode to the B-mode.

[00131] FIG. 16 depicts plots of the angular velocity and the attitude of the UAV 900 during the transition from the B-mode to the M-mode and then back to the B-mode, according to various example embodiments of the present invention. In FIG. 16, a slight disturbance was experienced around 40 seconds into the flight, which can be ignored.

[00132] FIGs. 17A and 17B depict the thrust and actuator output commands/signals output from the mode transition controller for controlling the first thrust unit 930, the second thrust unit 932, the first actuator 940 and the second actuator 942 (referred to as ‘Motorl’, ‘Motor2’, ‘ServoT and ‘Servo2’, respectively, in FIGs. 17A and 17B) during the transition from the B- mode to the M-mode and then back to the B-mode, according to various example embodiments of the present invention, while zooming in on the transition region. The data was recorded at 4 Hz.

[00133] Accordingly, various example embodiments provide a single-wing rotorcraft that can fly in multiple different types of flight modes, including the M-mode (based on monocopter platform) and the B-mode (based on bicopter platform), as well as transition technique/ strategy and control thereof. The single-wing rotorcraft is able to take off and land in both flight modes, as well as perform mid-air transitions from one flight mode to another flight mode. In various example embodiments, the single-wing rotorcraft utilizes two actuators (e.g., the second thrust unit 532/932 and the second actuator 542/942) for flight in the M-mode and utilizes all four actuators (e.g., the first thrust unit 530/930, the second thrust unit 532/932, the first actuator 540/940 and the second actuator 542/942) for a stable flight in the B-mode. As an example practical application, the single-wing rotorcraft is able to achieve better position and attitude control while flying in the B-mode, whereas it can utilize the M-mode for hovering to conserve battery. For example, the M-mode can also be utilized to use a LiDAR sensor for 3D mapping of the environment, and in case of power failure, it can help descent safely using the inherent autorotation capability. In various example embodiments, a technique is provided for enabling the control of the angular velocity of the single-wing rotorcraft while hovering in the M-mode. In addition, experimental results have been presented for the position control of the single-wing rotorcraft in both flight modes. The experimental results demonstrate that the single-wing rotorcraft is fully controllable (i.e., position and orientation) in both flight modes, while having more flight stability and control in the B-mode. Along with the position control, relevant data showing the transition from one mode to another was presented. Furthermore, the blending and transition method implemented according to various example embodiments produced good results, demonstrating the viability and effectiveness of the single-wing rotorcraft to switch flight modes mid-air. Accordingly, by combining the spinning monocopter platform with a stable bicopter platform, the single-wing rotorcraft according to various example embodiments has more practical real-world applications, compared to the previous works presented on conventional platforms with (only) a single flight mode (e.g., conventional monocopters and bicopters). Accordingly, various example embodiemnts advangtageously provide a single-wing rotorcraft with multiple flight modes in an effective manner for enabling the single-wing rotorcraft to be adaptable in an operating environment during flight and be employable in a wider range of practical applications.

[00134] While embodiments of the invention have been particularly shown and described with reference to specific embodiments, it should be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the scope of the invention as defined by the appended claims. The scope of the invention is thus indicated by the appended claims and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced.