Multi-rotor aerial vehicle with single arm failure redundancy

Abstract

The present disclosure provides a multi-rotor Aerial Vehicle comprising at least five arms. Pairs of coaxial contra rotating rotors/propellers are configured on each arm defining a polygon. In the event of failure of any one of the rotors/propellers, a control system incorporating an autopilot, shuts off corresponding contra rotating rotor/propeller of the pair to maintain yaw stability thereby rendering the corresponding arm non-functional; and adjusts throttles of the coaxial contra rotating rotors/propellers of remaining functional arms to maintain tilt and lift stability of the Aerial Vehicle.

Claims

1. A multi-rotor Aerial Vehicle comprising: a frame having at least five arms; pairs of contra rotating coaxial rotors/propellers configured on each arm of the frame; and a control system incorporating an autopilot configured to control operation of the pairs of contra rotating coaxial rotors/propellers to maintain stability of the Aerial Vehicle; wherein the pairs of contra rotating coaxial rotors/propellers are configured such that lines joining the adjacent contra rotating coaxial rotors/propellers define a polygon of a configuration such that in event of any one pair of the pairs of the contra rotating coaxial rotors/propellers becoming non-functional, centre of gravity of the Aerial vehicle still lies within a polygon formed by lines joining the adjacent pairs of contra rotating coaxial rotors/propellers that remain functional; and wherein the control system is configured such that in event of failure of any one of the rotors/propellers of the pairs of contra rotating coaxial rotors/propellers, the auto pilot shuts off corresponding contra rotating rotor/propeller of the pair, rendering the corresponding pair of the contra rotating coaxial rotors/propellers non-functional, to maintain yaw stability.

2. The Aerial Vehicle of claim 1, wherein the pairs of contra rotating coaxial rotors/propellers are configured such that lines joining the adjacent contra rotating coaxial rotors/propellers define a regular polygon with centre of gravity of the Aerial vehicle substantially coinciding with centre of the polygon.

3. The Aerial Vehicle of claim 1, wherein the pairs of contra rotating coaxial rotors/propellers are configured such that lines joining the adjacent contra rotating coaxial rotors/propellers define an irregular convex polygon.

4. The Aerial Vehicle of claim 1, wherein in the event of failure of any one of the rotors/propellers, the autopilot also throttles up or throttles down functional pairs of contra rotating coaxial rotors/propellers depending on location of the functional pairs of contra rotating coaxial rotors/propellers in relation with the non-functional arm to maintain tilt and lift stability of the Aerial Vehicle.

5. The Aerial Vehicle of claim 4, wherein in the event of failure of any one of the rotors/propellers, the autopilot maintains lift stability by throttling up or throttling down the functional pairs of contra rotating coaxial rotors/propellers such that sum of lifting forces of the individual pairs of contra rotating coaxial rotors/propellers is equal to weight of the Aerial Vehicle.

6. The Aerial Vehicle of claim 4, wherein in the event of failure of any one of the rotors/propellers, autopilot maintains tilt stability by throttling up or throttling down the functional pairs of contra rotating coaxial rotors/propellers so as to move centre of lift to make the centre of lift coincide with centre of gravity of the Aerial Vehicle.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The accompanying drawings are included to provide a further understanding of the present disclosure, and are incorporated in and constitute a part of this specification. The drawings illustrate exemplary embodiments of the present disclosure and, together with the description, serve to explain the principles of the present disclosure.

(2) FIG. 1 illustrates an exemplary representation of a multi-rotor Unmanned Aerial Vehicle (UAV) in accordance with an embodiment of the present disclosure.

(3) FIG. 2 illustrates another exemplary representation of a multi-rotor UAV, in accordance with an embodiment of the present disclosure

(4) FIG. 3 illustrates an exemplary block diagram to explain single arm redundancy in a multi-rotor UAV in accordance with an embodiment of the present disclosure.

(5) FIG. 4 illustrates an exemplary representation of an irregular convex configuration of the pairs of contra rotating coaxial rotors/propellers in accordance with an embodiment of the present disclosure.

DETAILED DESCRIPTION

(6) The following is a detailed description of embodiments of the disclosure depicted in the accompanying drawings. The embodiments are in such detail as to clearly communicate the disclosure. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.

(7) Each of the appended claims defines a separate invention, which for infringement purposes is recognized as including equivalents to the various elements or limitations specified in the claims. Depending on the context, all references below to the invention may in some cases refer to certain specific embodiments only. In other cases it will be recognized that references to the invention will refer to subject matter recited in one or more, but not necessarily all, of the claims.

(8) Various terms as used herein are shown below. To the extent a term used in a claim is not defined below, it should be given the broadest definition persons in the pertinent art have given that term as reflected in printed publications and issued patents at the time of filing.

(9) The term yaw as used herein refers to a side to side movement of the nose or rotation or heading of a multi-rotor UAV about its vertical axis passing through its centre of gravity

(10) The term lift force as used herein refers to various forces in an UAV enabling it to be lifted up.

(11) The term centre of lift as used herein refers to the point on an UAV where sum total of all lift forces generated by all rotors can be represented as an aggregate force with its direction.

(12) The term throttle as used herein refers to a mechanism to vary the lift forces of a UAV, generally by varying speed of its rotor assemblies that drives its propellers.

(13) The term moment of force as used herein refers to the tendency of a force to rotate an object about an axis, fulcrum, or pivot.

(14) The present disclosure relates to the field of aerial vehicles. More particularly, the present disclosures relates to a multi-rotor aerial vehicle that can operate even if one of its rotor assembly and/or associated components fail for any reason.

(15) While the exemplary embodiments of the invention have been described hereunder with reference to a 5-armed rigid frame multi-rotor UAV, the scope of the invention applies to any aerial vehicle manned or unmanned that can use similar means and principles for achieving stability and/or altitude while in flight.

(16) FIG. 1 illustrates an exemplary representation of a multi-rotor Unmanned Aerial Vehicle (UAV) in accordance with an embodiment of the present disclosure.

(17) In an aspect, the UAV 100 can have rotor assemblies shown as A1, A2, A3, A4 and A5 that can be configured with motors.

(18) In another aspect, each rotor assembly can be configured to carry a pair of coaxial propellers shown as P1-1 and P1-2 for rotor assembly A1, P2-1 and P2-2 for rotor assembly A2, P3-1 and P3-2 for rotor assembly A3, P4-1 and P4-2 for rotor assembly A4 and P5-1 and P5-2 for rotor assembly A5.

(19) In an aspect, the rotor assemblies can be configured to be throttled up or down through their motors and, in consequence, increase or decrease the lift force provided by the corresponding propellers.

(20) In another aspect, coaxial propellers can be configured to rotate in opposite directions thereby balancing each other's torque. In another aspect, the coaxial propellers can be configured to deliver required lift forces to the UAV. In an exemplary embodiment, to maintain a stable altitude in flight of UAV 100, all the coaxial propellers can be configured to deliver equal lift force, the sum of which can be equal to the sum of weight of UAV 100 and the weight to be carried (called total weight hereinafter) and can keep the sum of the moment of lift forces at the centre of gravity point of UAV 100 as zero so that UAV 100 does not tilt in any direction and does not become unstable in flight.

(21) In an exemplary embodiment, the rotor assemblies can be connected in a 5-armed assembly to central hub 102 using any appropriate means as may be required to ensure a rigid and low/no vibration mounting of each co-axial propeller pair, such that all the coaxial propeller pairs are joined to central hub 102 in a pentagonal arrangement. In an exemplary embodiment such connection can be by means of five arms 104-1, 104-2, 104-3, 104-4 and 104-5 as shown in FIG. 1 thus providing a 5-armed rigid frame coaxial propeller configuration.

(22) In an aspect, the propeller arrangement along a UAV arm may be on the same side or on its opposite sides.

(23) It is to be appreciated that though embodiment shown in FIG. 1 (and also FIG. 2) have five rotors/propellers positioned in a regular polygon configuration, it is possible to have them in an irregular convex polygon of shape, such as shown in FIG. 4, such that in event of failure of any one arm, the CG of UAV still lies well within the minimum support polygon formed by the remaining four arms that are still functioning thus providing capability of maintaining stability and yaw control even in the event of failure of one arm of UAV.

(24) In another aspect, in the event of failure for any reason of one propeller of a rotor assembly mounted on any arm, autopilot of UAV 100 can switch off motor(s) corresponding to that rotor assembly/arm so as to as well stop other coaxially placed propeller on that rotor, effectively disabling that arm of the UAV and serving to balance the yaw component.

(25) FIG. 2 illustrates another exemplary representation of a multi-rotor Unmanned Aerial Vehicle 200 in accordance with an embodiment of the present disclosure. As shown in FIG. 2, the UAV 200 can comprise five sides such as 202, 204, 206, 208 and 210 formed by joining vertices of a regular pentagon. Located at each vertex can be a rotor assembly comprising a pair of contra rotating coaxial propellers. Polygon thus formed can be supported by a suitable structure such as a triangular structure shown in FIG. 2 and, therefore, each of the rotor may not be connected to UAV body by a radial arm emanating from the UAV body. Any reference to a rotor arm in the disclosure shall include rotor of such configuration even though there may not be any arm per se.

(26) In an aspect, the UAV 100 can further include a control system that incorporates an auto pilot configured to control throttle of the rotors based on operating condition of the UAV and its functional systems.

(27) FIG. 3 illustrates an exemplary block diagram 300 to explain single arm redundancy in a multi-rotor UAV such as UAV 100 (or UAV 200 and any reference to UAV

(28) 100 hereinafter should be construed to include UAV 200). The lift forces created by combination of the rotors when rotating at equal speeds can be equal and accordingly (considering that mass is symmetrically distributed in the UAV) under that condition centre of lift of UAV 100/200 can coincide with its centre of gravity at point A as shown in FIG. 3. In alternate scenario, the rotors may be configured to run at different speeds so as to have centre of lift coinciding with the centre of gravity A of the UAV to provide it a stable condition.

(29) During flight of UAV 100 any number of untoward accidents can occur that can lead to failure of any one of the rotor assemblies or its propellers or any one of UAV arm or any combination of these. Dust or small particulate matter can enter and damage the motors, excessive moisture can lead to corrosion of the motor shafts, motor driver can malfunction, or in another scenario, motor overheating can lead to deterioration of winding insulation and damage internal wiring of the system. Impact collisions with obstacles may cause mechanical damage to an arm of the UAV, UAV propeller blade may break off, or scratches/cracks on blades may grow over time and eventually lead to failure.

(30) In an exemplary embodiment of the present disclosure, let us assume that one of the two contra rotating propellers of one arm, say P3-1 fails due to any of the failure scenarios stated above. In an aspect, the system of the present disclosure can have appropriately configured sensors on UAV 100 that can sense such failure and can direct its autopilot to shut off the corresponding rotor assembly, A3 in the present case.

(31) In another aspect, once rotor assembly A3 has been shutoff and the lift forces provided by the remaining rotor assemblies remaining same as before, the centre of lift can shift to point B away from the centre of gravity point A (along line joining A3 to A in direction opposite to A3) as shown in FIG. 2. In such a situation, the sum of moment of forces on the centre of gravity point A will not be equal to zero and accordingly UAV 100 can start tilting about a horizontal axis perpendicular to line joining centre of A3 to centre of gravity point A such as line 302 (hereinafter referred to as axis of tilt or tilt axis 302), and consequently that can cause further reduction in lift forces and drifting aside of the UAV 100, finally causing UAV 100 to become unstable and crash. This can be avoided by adjusting lift forces of the remaining arms by throttle adjustment of the corresponding rotor assemblies as disclosed in the present disclosure.

(32) In an aspect, the system of the present disclosure can be configured to provide such appropriate throttling signals to the relevant rotor assemblies so that the lift forces provided by the propellers of each arm can be increased or decreased from their initial values in order that sum of moment of lift forces on the centre of gravity point A can again be made zero and the UAV 100 remain stable.

(33) In an aspect, two rotor assemblies (A1, A5) that are farther away from tilt axis 302 can be throttled down to decrease the lift force of their propellers in such a fashion that sum of moment of lift forces on centre of gravity point A can again be made zero and UAV 100 remain stable.

(34) In another aspect, two rotor assembles (A2, and A4) that are nearer to tilt axis 302 can be throttled up to increase lift force of their propellers in such a fashion that sum of moment of lift forces on centre of gravity point A can again be made zero and UAV 100 remain stable.

(35) In yet another aspect, each of the remaining rotor assemblies A1, A2, A5 and A4 can be individually throttled up and down to increase or decrease lift forces of their attached propellers in such a fashion that sum of moment of lift forces on the centre of gravity point A can again be made zero and the UAV 100 remain stable.

(36) In an exemplary embodiment, once rotor assembly A3 is shut down, centre of lift of UAV 100 can shift to point B closer to rotor assemblies A1 and A5, and farther from rotor assemblies A2 and A4. As would be apparent, new lift centre B (when remaining rotor assemblies are working to provide equal lift i.e. before they are throttled up or down) would take a position such that all four working rotors are equidistance from a line 304 passing through the new lift centre B and parallel to the tilt axis 302. In an aspect, system of the present disclosure can readjust the throttles of remaining working rotor assemblies such as A1, A2, A4 and A5, so that sum of moment of lift forces on the centre of gravity point A can again be quickly made zero shifting the lift centre B back to coincide with the centre of gravity A and make the UAV 100 stable.

(37) In an exemplary embodiment, the system of present disclosure can maintain sum of moment of lift forces (in their vector form) on the centre of gravity point A as zero by adjusting the throttles to the still rotor assemblies as explained below. The throttles to the rotor assemblies that are still working can be varied so that following scalar equations are satisfied:
(LfA1)*L1=(LfA2)*L2 and
(LfA5)*L5=(LfA4)*L4

(38) Where L1, L2, L4 and L5 are distances of the working rotor assemblies such as A1, A2, A4 and A5 respectively from axis of tilt 302; and LfA1, LfA2 etc. are lift forces provided by respective rotor assemblies such as A1, A2 etc.

(39) In an aspect, distances of the working rotor assemblies such as L1, L2, L4 and L5 can be determined by system of the present disclosure taking into consideration location of the corresponding rotor assembly in relation with the failed rotor assembly.

(40) In another aspect, total lift force on UAV 100 can be initially provided by summation of lift forces provided by each of the propellers provided on the rotor assemblies A1, A2, A3, A4 and A5 of UAV 100. After one rotor assembly has shut down the total lift force can reduce and so UAV 100 can lose altitude and/or become unstable, unless the lift forces of the remaining arms are adjusted.

(41) In an embodiment, in such a case, lift forces of the remaining propellers can be increased by providing more throttle to their rotor assemblies so that the sum of lift forces with the remaining four propellers driven by their corresponding rotor assemblies once again

(42) becomes equal to the total weight of UAV 100 and so, UAV 100 can maintain altitude and equilibrium.

(43) That is, in an aspect, while all rotor assemblies are functional, the system of the present disclosure can be configured so that the total lift provided by the rotor assemblies equals the total weight of UAV 100. This can be shown as:
(LfA1)(LfA2(LfA3)(LfA4)(LfA5)=Total Weight of UAV

(44) In another aspect, the system of the present disclosure can be configured such that once one rotor assembly, say A5 has been shut down, the total lift provided by the remaining rotor assemblies equals the total weight of UAV 100, while maintaining the centre of gravity of UAV 100 as before. This under the exemplary condition of failure of A3 can be shown as:
(LfA1)(LfA2(LfA4)(LfA5)=Total Weight of UAV

(45) The present disclosure provides for an invention that enables minimum number of arms to achieve redundancy in a static multi-rotor UAV configuration. Also, loss of lift force due to isolation of one arm out of five arms is only 20%, achieving higher lift force at redundancy compared to configurations which require two arms to be shut down upon single motor/propeller failure. The invention describes the minimum arm configuration required to operate a multi-rotor UAV in the event of one arm failure.

(46) In an aspect, the functioning rotors are throttled up or throttled down depending on their location in relation with the failed arm to maintain lift and tilt stability. The tilt stability is maintained by throttling up or throttling down the other rotors so as to move centre of lift to make it coincide with the CG. Lift stability is maintained by throttling up or throttling down the other rotors so that sum of lifting forces of the individual rotors/propellers is equal to weight of the UAV.

(47) In an embodiment, the UAV can have five arms each of the arms incorporating a pair of contra rotating propellers. The 5-armed rigid frame configuration using coaxial propellers can provide best redundancy with minimum number of arms and minimum penalty on throttle margin due to shutting down of a single arm due to propeller/motor/driver failure in that arm.

(48) In an embodiment, the UAV can have a fixed pitch propeller mechanism or a variable pitch propeller system without any limitation.

(49) It is contemplated that various combinations and/or sub-combinations of the specific features and aspects of the above embodiments may be made and still fall within the scope of the invention. Accordingly, it should be understood that various features and aspects of the disclosed embodiments may be combined with or substituted for one another in order to form varying modes of the disclosed invention. Further, it is intended that the scope of the present invention herein disclosed by way of examples should not be limited by the particular disclosed arrangements described above.

(50) While the foregoing describes various embodiments of the invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof. The scope of the invention is determined by the claims that follow. The invention is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art.

ADVANTAGES OF THE INVENTION

(51) The present disclosure provides a reliable and cost effective multi-rotor rigid frame UAV.

(52) The present disclosure provides a multi-rotor UAV with inbuilt single arm failure redundancy so as to improve its reliability.

(53) The present disclosure provides single arm failure redundancy in a multi-rotor UAV keeping number of arms/rotors to a minimum.

(54) The present disclosure provides inbuilt single arm failure redundancy that takes care of lift, yaw, pitch and roll requirements of the multi-propeller UAV.