SYSTEMS AND METHODS FOR STABILISATION OF AERIAL VEHICLES

Abstract

A rotor assembly for a multirotor aircraft, and a multirotor aircraft, are disclosed herein. The rotor assembly has a first motor having a first axis of rotation and a first propeller connected to the first motor. The rotor assembly has a second motor having a second axis of rotation, and a second propeller connected to the second motor. The second propeller is smaller in length than the first propeller. The first motor and the first propeller produce a greater proportion of a total lift thrust of the rotor assembly than the second motor and the second propeller. The multirotor aircraft includes an airframe and a plurality of the rotor assemblies mounted to the airframe.

Claims

1. A multirotor aircraft, including: an airframe; a plurality of rotor assemblies mounted to the airframe, each rotor assembly including: a first motor having a first axis of rotation; a first propeller connected to the first motor; a second motor having a second axis of rotation; a second propeller connected to the second motor, wherein the second propeller is smaller in length than the first propeller, and wherein the first motor and the first propeller of each rotor assembly produce a greater proportion of a total lift thrust of the rotor assembly than the second motor and the second propeller of the rotor assembly.

2. The multirotor aircraft of claim 1, wherein the first motor and the first propeller of each rotor assembly are configured to produce between about 55 to 75 percent of the total lift thrust of the rotor assembly, and the second motor and the second propeller are configured to produce between about 45 to 25 percent of the total lift thrust.

3. The multirotor aircraft of claim 2, wherein the first motor and the first propeller of each rotor assembly are configured to produce between about 55 to 65 percent of the total lift thrust of the rotor assembly, and the second motor and the second propeller are configured to produce between about 45 to 35 percent of the total lift thrust.

4. The multirotor aircraft of claim 1, wherein the motor velocity constant of the first motor of each rotor assembly is smaller than that of the second motor of the rotor assembly.

5. The multirotor aircraft of claim 1, including a controller configured to control the first motors and second motors, wherein the first motors are controlled by a first control loop, and the second motors are controlled by a second control loop.

6. The multirotor aircraft of claim 1, wherein the first axis of rotation of the first motor of each rotor assembly is coaxial with the second axis of rotation with the second motor of the rotor assembly.

7. The multirotor aircraft of claim 1, wherein the first axis of rotation of the first motor of each rotor assembly is laterally offset from the second axis of rotation with the second motor of the rotor assembly.

8. The multirotor aircraft of claim 7, wherein the first motor and first propeller of each rotor assembly are positioned further from a centre of the airframe than the second motor and second propeller.

9. The multirotor aircraft of claim 8, wherein the airframe includes a plurality of booms to which the rotor assembles are mounted, and wherein the lateral offset between the first and second motors of each rotor assembly are achieved by spacing the motors apart along one of the booms.

10. The multirotor aircraft of claim 1, wherein the first motor and the first propeller of each rotor assembly are positioned above the second motor and the second propeller of the respective rotor assemblies.

11. The multirotor aircraft of claim 1, wherein the first motor and the second motor of each rotor assembly are configured to counter-rotate.

12. The multirotor aircraft of claim 1, wherein the first motor and the second motor of each rotor assembly are configured to rotate in the same direction.

13. The multirotor aircraft of claim 1, wherein the first propeller and the second propeller of each rotor assembly have a different number of blades.

14. The multirotor aircraft of claim 13, wherein the first propeller of each rotor assembly has more blades than the second propeller.

15. The multirotor aircraft of claim 15, wherein the first propeller has more than two blades.

16. The multirotor aircraft of claim 13, wherein the first propeller of the rotor assembly is a three blade propeller, and the second propeller is a two blade propeller.

17. A rotor assembly for a multirotor aircraft, including: a first motor having a first axis of rotation; a first propeller connected to the first motor; a second motor having a second axis of rotation; a second propeller connected to the second motor, wherein the second propeller is smaller in length than the first propeller, and wherein the first motor and the first propeller produce a greater proportion of a total lift thrust of the rotor assembly than the second motor and the second propeller.

18. A method of operating a multirotor aircraft including an airframe, and a plurality of rotor assemblies mounted to the airframe, each rotor assembly including a first motor having a first axis of rotation with a first propeller connected to the first motor, and a second motor having a second axis of rotation and a second propeller connected to the second motor, wherein the second propeller is smaller in length than the first propeller, the method including the step of: controlling the first motor and the second motor of each rotor assembly such that the first motor and the first propeller produce a greater proportion of a total lift thrust of the rotor assembly than the second motor and the second propeller of the rotor assembly.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Further aspects of the present invention will become apparent from the ensuing description which is given by way of example only and with reference to the accompanying drawings in which:

[0045] FIG. 1A is a side view of an exemplary multirotor aircraft according to an exemplary embodiment of the present disclosure;

[0046] FIG. 1B is a top view of the exemplary multirotor aircraft;

[0047] FIG. 1C is a side view of an exemplary rotor assembly for use with the exemplary multirotor aircraft;

[0048] FIG. 1D is a side view of another exemplary rotor assembly for use with the exemplary multirotor aircraft;

[0049] FIG. 2A is a top view of a second exemplary multirotor aircraft;

[0050] FIG. 2B is a side view of an exemplary rotor assembly for use with the second exemplary multirotor aircraft;

[0051] FIG. 3A is a schematic diagram of an exemplary flight system of the exemplary multirotor aircraft;

[0052] FIG. 3B is a schematic diagram of an exemplary flight controller of the exemplary multirotor aircraft;

[0053] FIG. 3C illustrates an exemplary ground control system in communication with the exemplary multirotor aircraft;

[0054] FIG. 4 is a flow diagram illustrating a method of stabilising the exemplary multirotor aircraft in flight, and

[0055] FIG. 5 is a graph of proportional thrust percentages and sensitivity settings of the exemplary rotor assembly.

DETAILED DESCRIPTION

[0056] FIG. 1A and FIG. 1B illustrate an unmanned multirotor aircraft 100 in an X8 configuration, herein referred to as UAV 100. As seen in FIG. 1A, the airframe of the UAV 100 includes a hull 102 supported by a landing base 104. Arms 106 (labelled arms 106a-d in FIG. 1B) extend from the hull 102, with rotor assemblies 108 (labelled rotor assemblies 108a-d in FIG. 1B) secured to the distal ends of the arms 106. It should be appreciated that while the arms 106 are illustrated as being pitched up from the hull 102, this is not intended to be limiting to all embodiments.

[0057] Each rotor assembly 108 includes a top motor 110 (labelled top motors 110a-d in FIG. 1B), to which a top propeller 112 (labelled top propellers 112a-d in FIG. 1B) is secured. Each rotor assembly 108 includes a bottom motor 114 (labelled bottom motors 114a-d in FIG. 1B), to which a bottom propeller 116 (labelled bottom propellers 116a-d in FIG. 1B) is secured. Referring to FIG. 1B, it may be seen that in this exemplary embodiment each of the rotor assembly 108a-d is equidistant from adjacent rotor assemblies.

[0058] FIG. 1C shows an exemplary rotor assembly configuration 118a for the UAV 100. In this exemplary embodiment the top motor 110a is a brushless DC motor having a motor velocity constant of 170 KV, with the top propeller 112a being a 28?8 two blade propeller (i.e. 28 inches in length or diameter, with a pitch of 8). The bottom motor 114a is a brushless DC motor having a motor velocity constant of 340 KV, with the bottom propeller 116a being 18?6.5. It should be appreciated that these values are given by way of example, and are not intended to be limiting to all embodiments subject of the present disclosure. In the configuration illustrated, the top axis of rotation 120a of the top motor 110a is substantially aligned with the bottom axis of rotation 122a of the bottom motor 114ai.e. is co-axial.

[0059] In the case of a power supply in the form of a 6s battery (i.e. a six cell battery with a nominal voltage of 22.2V), the thrust values produced by each of the rotor assemblies 108a-d are outlined below in Table 1.

TABLE-US-00001 TABLE 1 % Overall Motor Power Throttle Thrust (g) Prop RPM thrust load 170 kv 6s 50% 1805 1650 57.67 340 kv 6s 1325 3636 42.33 170 kv 6s 65% 2780 2050 55.38 340 kv 6s 2240 4641 44.62 170 kv 6s 75% 3440 2250 54.82 340 kv 6s 2835 5211 45.18 170 kv 6s 85% 4140 2450 55.20 340 kv 6s 3360 5628 44.80 170 kv 6s 100% 4570 2620 52.50 340 kv 6s 4135 6181 47.50

[0060] FIG. 1D shows an exemplary rotor assembly configuration 124 in which the characteristics of the top and bottom motors and propellers are switched in comparison with assembly 118ai.e. the top motor 110a has a motor velocity constant of 340 KV with the top propeller 112a being 18?6.5, while the bottom motor 114a has a motor velocity constant of 170 KV, with the bottom propeller 116a being 28?8.

[0061] FIG. 2A illustrates a second exemplary unmanned multirotor aircraft 200, herein referred to as UAV 200. The airframe of the UAV 200 includes a hull 202 supported by a landing base (not illustrated, but refer to landing base 104 of FIG. 1A as an example). Arms 204a-d extend from the hull 202, having a first cross-brace 206a between arms 204a and 204b, and a second cross-brace 206b between arms 204b and 204c.

[0062] The UAV 200 includes four rotor assemblies 208a-d. Each rotor assembly 208a-d includes a top motor 210a-d, to which a top propeller 212a-d is secured. Each rotor assembly 208a-d includes a bottom motor 214a-d, to which a bottom propeller 116a-d is secured. The top motors 210a-d are laterally offset from the bottom motors 214a-d along the arms 204a-d, with the bottom motors 214a-d closer to the hull 202. As shown in FIG. 2B, the arm 204a includes a first shroud 218a in which the top motor 210a is received and mounted, and a second shroud 220a in which the bottom motor 214a is received and mounted.

[0063] Returning to FIG. 2A, in this exemplary embodiment each of the top propellers 212a-d are a 27.5?8.9 three blade propeller and each of the bottom propellers 216a-d are a 18.5?6.3 two blade propeller. In this exemplary embodiment the top motor 210a is a brushless DC motor having a motor velocity constant of 170 KV, and the bottom motor 214a is a brushless DC motor having a motor velocity constant of 340 KV. Again, it should be appreciated that these values are given by way of example, and are not intended to be limiting to all embodiments subject of the present disclosure.

[0064] FIG. 3A illustrates an exemplary flight control system 300 for the UAV 100 or 200. The system 300 includes an on-board flight controller 302, controlling delivery of power from a battery 304 (for example, a lithium polymer battery) to the top motors 110a-d/210a-d and bottom motors 114a-d/214a-d via Electronic Speed Controllers (ESCs) 306a-h to control the speed and direction of the motors.

[0065] The system 300 includes GPS antennas 308a and 308b, as well as a radio frequency transceiver 310. A imaging devicefor example a camera 312is fitted to a controllable gimbal 314.

[0066] Referring to FIG. 3B, the flight controller 302 includes a master controller 316a and a slave controller 316b. Each controller 316a and 316b includes at least one microprocessor 318a and 318b, an inertial measurement unit 320a and 320b, and an onboard compass 322a and 322b. Each controller 316a and 316b are connected to respective GPS modules 324a and 324b. The master controller 316a is also connected to communications modules in the form of an RC receiver unit 324 and a wireless communications module 326 (for example using WiFi or Bluetooth).

[0067] While the flight controller 302 may allow for a number of automated flight modes and functions, the UAV 100 or 200 may communicate with a ground control unit 350, as seen in FIG. 3C. The ground control unit 350 includes user controls 352 for manual control of aspects of the UAV's operation, with a first display device 354 showing a live camera feed from camera 312, and a second display device 356 showing telemetry information.

[0068] Referring to FIG. 4, the control system 302 is configured to stabilize the UAV 100 or 200 using a method 400 in which flight metrics such as yaw and pitch are monitored, and in response to determining that level flight is not being achieved in step 402, the controller proportionally controls the speed of the motors 110a-d/210a-d and 114a-d/214a-d in response in step 404.

[0069] In an exemplary embodiment, the top motors 110a-d/210a-d are controlled by a first feedback control loop having a first set of proportional control settings (for example PID values for each of the top motors 110a-d/210a-d), and the bottom motors 114a-d/214a-d are controlled by a second feedback control loop having a second set of proportional control settings (for example PID values for each of the bottom motors 114a-d/214a-d).

[0070] Tuning of the control settings may be performed by tuning the top motors 110a-d/210a-d separately from the bottom motors 114a-d/214a-di.e. tuning the top motors 110a-d/210a-d while the bottom motors 114a-d/214a-d are not running, and vice versa. Reference to tuning should be appreciated to mean adjusting the values of the PID parameters to achieve desired flight characteristics. By tuning the top and bottom motors separately, the control settings can be tailored to the distinct performance characteristics created by the differences in motor and propeller specifications.

[0071] It is envisaged that tuning may start from a general 60:40 thrust ratio distribution between the top motors 110a-d/210a-d separately from the bottom motors 114a-d/214a-d, with adjustments made in accordance with desired flight characteristicsfor example, balancing power draw for flight time against sensitivity for stability.

[0072] An exemplary configuration of the sensitivity of the control of each motor pairi.e. the extent to which motor speed is adjusted in response to deviations from stable flightas well as the proportional contribution to total lift thrust at a number of throttle percentages is illustrated in FIG. 5. It may be seen that at 50% throttlewhich in this case is intended to achieve hover flight of the UAVthe sensitivity of the smaller propeller/motor combination (expressed as a percentage of the maximum sensitivity setting capable by the control system 302) is proportionally much higher than that of the larger propeller/motor combination.

[0073] Reference to any prior art in this specification is not, and should not be taken as, an acknowledgement or any form of suggestion that that prior art forms part of the common general knowledge in the field of endeavor in any country in the world.

[0074] The disclosure may also be said broadly to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, in any or all combinations of two or more of said parts, elements or features.

[0075] Wherein the foregoing description reference has been made to integers or components having known equivalents thereof, those integers are herein incorporated as if individually set forth.

[0076] It should be noted that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications may be made without departing from the spirit and scope of the disclosure and without diminishing its attendant advantages. It is therefore intended that such changes and modifications be comprised within the present disclosure.

[0077] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. 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.

[0078] Explicitly referenced embodiments herein were chosen and described in order to best explain the principles of the disclosure and their practical application, and to enable others of ordinary skill in the art to understand the disclosure and recognize many alternatives, modifications, and variations on the described example(s). Accordingly, various implementations other than those explicitly described are within the scope of the disclosure, and it should be appreciated that modifications and additions may be made thereto without departing from the scope thereof as defined in the appended claims.