Maintaining attitude control of unmanned aerial vehicles using pivoting propulsion motors

Abstract

Aerial vehicles may be configured to control their attitudes by changing one or more physical attributes. For example, an aerial vehicle may be outfitted with propulsion motors having repositionable mounts by which the motors may be rotated about one or more axes, in order to redirect forces generated by the motors during operation. An aerial vehicle may also be outfitted with one or more other movable objects such as landing gear, antenna and/or engaged payloads, and one or more of such objects may be translated in one or more directions in order to adjust a center of gravity of the aerial vehicle. By varying angles by which forces are supplied to the aerial vehicle, or locations of the center of gravity of the aerial vehicle, a desired attitude of the aerial vehicle may be maintained irrespective of velocity, altitude and/or forces of thrust, lift, weight or drag acting upon the aerial vehicle.

What is claimed is: 
     
         1 . An unmanned aerial vehicle comprising:
 an airframe;   a first servo motor;   a first propulsion motor rotatably mounted to the airframe along a first mounting axis, wherein the first propulsion motor is configured to rotate a first propeller about a first propeller axis, wherein the first servo motor is configured to rotate the first propulsion motor about the first mounting axis, and wherein the first propeller axis is perpendicular to the first mounting axis;   a second servo motor;   a second propulsion motor rotatably mounted to the airframe along a second mounting axis, wherein the second propulsion motor is configured to rotate a second propeller about a second propeller axis, wherein the second servo motor is configured to rotate the second propulsion motor about the second mounting axis, and wherein the second propeller axis is perpendicular to the second mounting axis; and   a control system having at least one computer processor configured to at least:
 identify a mission to be performed using the aerial vehicle, wherein the mission comprises at least a first leg requiring the aerial vehicle to travel on a first course and at a first speed in a first orientation; 
 determine at least one of a first net forward force, a first net lateral force and a first net vertical force required for the aerial vehicle to complete the first leg of the mission; 
 select a first operating speed and a first alignment of the first propulsion motor based at least in part on the first course, the first speed and the first orientation; 
 select a second operating speed and a second alignment of the second propulsion motor based at least in part on the first course, the first speed and the first orientation; 
 determine a first forward force, a first lateral force and a first vertical force based at least in part on the first operating speed and the first alignment; 
 determine a second forward force, a second lateral force and a second vertical force based at least in part on the second operating speed and the second alignment, wherein a sum of the first forward force and the second forward force is at least the first net forward force, wherein a sum of the first lateral force and the second lateral force is at least the first net lateral force, and wherein a sum of the first vertical force and the second vertical force is at least the first net vertical force; 
 rotate, by the first servo motor, the first propulsion motor about the first mounting axis until the first propeller axis is in the first alignment; 
 rotate, by the second servo motor, the second propulsion motor about the second mounting axis until the second propeller axis is in the second alignment; 
 cause the first propulsion motor to operate at the first operating speed; and 
 cause the second propulsion motor to operate at the second operating speed. 
   
     
     
         2 . The unmanned aerial vehicle of  claim 1 , wherein the mission further comprises at least a second leg requiring the aerial vehicle to travel on a second course and at a second speed in a second orientation, and
 wherein the at least one computer processor is further configured to at least:   determine at least one of a second net forward force and a second net vertical force required for the aerial vehicle to complete the second leg of the mission;   select a third operating speed and a third alignment of the first propulsion motor based at least in part on the second course, the second speed and the second orientation;   select a fourth operating speed and a fourth alignment of the second propulsion motor based at least in part on the second course, the second speed and the second orientation;   determine a third forward force, a third lateral force and a third vertical force based at least in part on the third operating speed and the third alignment;   determine a fourth forward force, a fourth lateral force and a fourth vertical force based at least in part on the fourth operating speed and the fourth alignment, wherein a sum of the third forward force and the fourth forward force is at least the second net forward force, wherein a sum of the third lateral force and the fourth lateral force is at least the second net lateral force, and wherein a sum of the third vertical force and the fourth vertical force is at least the second net vertical force;   cause the third propulsion motor to operate at the third operating speed; and   cause the fourth propulsion motor to operate at the fourth operating speed.   
     
     
         3 . The unmanned aerial vehicle of  claim 2 , wherein the first orientation comprises at least one of a first yaw angle, a first pitch angle or a first roll angle,
 wherein the second orientation comprises at least one of a second yaw angle, a second pitch angle or a second roll angle,   wherein the first net forward force and the first net vertical force are determined based at least in part on at least one of the first yaw angle, the first pitch angle or the first roll angle, and   wherein the second net forward force and the second net vertical force are determined based at least in part on the at least one of the second yaw angle, the second pitch angle or the second roll angle.   
     
     
         4 . A method for operating an aerial vehicle, wherein the aerial vehicle comprises a first propulsion motor, a second propulsion motor, a third propulsion motor and a fourth propulsion motor, and
 wherein the method comprises:   causing the aerial vehicle to travel on a course at a speed and an altitude and in an angular orientation prior to a first time, wherein causing the aerial vehicle to travel on the course, at the speed and the altitude and in the angular orientation prior to the first time comprises:
 causing the first propulsion motor to operate at a first rotational speed and in a first orientation prior to the first time; 
 causing the second propulsion motor to operate at a second rotational speed and in a second orientation prior to the first time; 
 causing the third propulsion motor to operate at a third rotational speed and in a third orientation prior to the first time; and 
   causing the fourth propulsion motor to operate at a fourth rotational speed and in a fourth orientation prior to the first time;   identifying a fault in the first propulsion motor as of the first time;   causing the aerial vehicle to travel on the course at the speed and the altitude and in the angular orientation after the first time, wherein causing the aerial vehicle to travel on the course, at the speed and the altitude and in the angular orientation after the first time comprises:
 selecting at least one of a fifth rotational speed or a fifth orientation for the second propulsion motor based at least in part on the fault; 
 selecting at least one of a sixth rotational speed or a sixth orientation for the third propulsion motor based at least in part on the fault; 
 selecting at least one of a seventh rotational speed or a seventh orientation for the fourth propulsion motor based at least in part on the fault; 
 causing the second propulsion motor to operate at the fifth rotational speed or in the fifth orientation after the first time; 
 causing the third propulsion motor to operate at the sixth rotational speed or in the sixth orientation after the first time; and 
 causing the fourth propulsion motor to operate at the seventh rotational speed or in the seventh orientation after the first time. 
   
     
     
         5 . The method of  claim 4 , wherein identifying the fault in the first propulsion motor comprises at least one of:
 determining an electric current flowing to or from the first propulsion motor at the first time;   determining a voltage drop across the first propulsion motor at the first time;   determining that the first propulsion motor is operating at less than the second operating speed at the first time;   determining that the aerial vehicle is not traveling along the course at the speed at the first time;   determining that the aerial vehicle is not operating in the angular orientation at the first time;   determining that a temperature associated with the first propulsion motor exceeds a predetermined threshold;   analyzing an image depicting at least a portion of the first propulsion motor, wherein the image was captured at approximately the first time; or   analyzing acoustic energy emanating from the aerial vehicle, wherein the acoustic energy was captured at approximately the first time.   
     
     
         6 . The method of  claim 4 , further comprising:
 determining a net force required to cause the aerial vehicle to travel on the course at the speed and the altitude and in the angular orientation, wherein the net force comprises a magnitude and a direction,   wherein the at least one of the fifth rotational speed or the fifth orientation for the second propulsion motor is selected based at least in part on the fault and the net force.   
     
     
         7 . The method of  claim 4 , wherein the second propulsion motor is mounted to an airframe of the aerial vehicle by a repositionable mount aligned along a first axis with respect to the airframe,
 wherein the repositionable mount comprises a servo motor configured to rotate the second propulsion motor about one of the first axis or a second axis perpendicular to the first axis, and   wherein causing the second propulsion motor to operate at the fifth rotational speed or in the fifth orientation after the first time comprises:
 rotating the second propulsion motor from the second orientation to the fifth orientation by the servo motor after the first time. 
   
     
     
         8 . A method for operating an aerial vehicle, wherein the aerial vehicle comprises a first propulsion motor and a second propulsion motor, and
 wherein the method comprises:   determining a first net propulsion force required from at least the first propulsion motor and the second propulsion motor to maintain the aerial vehicle in a first angular orientation while traveling on a first course, at a first altitude and at a first speed;   selecting a first rotational speed and a first orientation for the first propulsion motor based at least in part on the first net propulsion force;   selecting a second rotational speed and a second orientation for the first propulsion motor based at least in part on the first net propulsion force;   causing the first propulsion motor to operate at the first rotational speed and in the first orientation prior to a first time;   causing the second propulsion motor to operate at the second rotational speed and in the second orientation prior to the first time;   with the first propulsion motor operating at the first rotational speed and in the first orientation,
 determining that the second propulsion motor is ineffective at the first time; and 
   in response to determining that the second propulsion motor is ineffective at the first time,
 selecting at least one of a third rotational speed or a third orientation for the first propulsion motor based at least in part on the first net propulsion force; and 
 causing the first propulsion motor to operate at the third rotational speed or in the third orientation at a second time, wherein the second time follows the first time. 
   
     
     
         9 . The method of  claim 8 , wherein the aerial vehicle further comprises a third propulsion motor and a fourth propulsion motor,
 wherein the method further comprises:
 causing the third propulsion motor to operate at a fourth rotational speed and in a fourth orientation prior to the first time; and 
 causing the fourth propulsion motor to operate at a fifth rotational speed and in a fifth orientation prior to the first time, 
   wherein the first propulsion motor generates a first propulsion force operating at the first rotational speed and in the first orientation,   wherein the second propulsion motor generates a second propulsion force operating at the second rotational speed and in the second orientation,   wherein the third propulsion motor generates a third propulsion force operating at the fourth rotational speed and in the fourth orientation,   wherein the fourth propulsion motor generates a fourth propulsion force operating at the fifth rotational speed and in the fifth orientation, and   wherein a sum of the first propulsion force, the second propulsion force, the third propulsion force and the fourth propulsion force is approximately equal to the first net propulsion force.   
     
     
         10 . The method of  claim 8 , wherein the first propulsion motor generates a fifth propulsion force operating at the third rotational speed or in the third orientation, and
 wherein a sum of the third propulsion force, the fourth propulsion force and the fifth propulsion force is approximately equal to the net propulsion force.   
     
     
         11 . The method of  claim 8 , wherein the first propulsion motor is mounted to an airframe of the aerial vehicle by a first repositionable mount along a first axis with respect to the airframe, and
 wherein the first repositionable mount comprises a first servo motor,   wherein the first servo motor is configured to rotate the first propulsion motor about one of the first axis or a second axis, and   wherein the second axis is perpendicular to the first axis.   
     
     
         12 . The method of  claim 8 , further comprising:
 determining a second net propulsion force required from at least the first propulsion motor to maintain the aerial vehicle in the first angular orientation while traveling on the first course, at the first altitude and at a second speed prior to a third time, wherein the third time follows the second time;   selecting a fourth rotational speed and a fourth orientation for the first propulsion motor based at least in part on the second net propulsion force; and   causing the first propulsion motor to operate at the fourth rotational speed and a fourth orientation at the third time.   
     
     
         13 . The method of  claim 8 , further comprising:
 determining a second net propulsion force required from at least the first propulsion motor to place the aerial vehicle in a second angular orientation while traveling on the first course, at the first altitude and at the first speed prior to a third time, wherein the third time follows the second time;   selecting a fourth rotational speed and a fourth orientation for the first propulsion motor based at least in part on the second net propulsion force; and   causing the first propulsion motor to operate at the fourth rotational speed and a fourth orientation at the third time.   
     
     
         14 . The method of  claim 8 , further comprising:
 determining a second net propulsion force required from at least the first propulsion motor to maintain the aerial vehicle in the first angular orientation while traveling on a second course, at the first altitude and at the third speed prior to a third time, wherein the third time follows the second time;   selecting a fourth rotational speed and a fourth orientation for the first propulsion motor based at least in part on the second net propulsion force; and   causing the first propulsion motor to operate at the fourth rotational speed and a fourth orientation at the third time.   
     
     
         15 . The method of  claim 8 , further comprising:
 determining a second net propulsion force required from at least the first propulsion motor to maintain the aerial vehicle in the first angular orientation while traveling on the first course, at a second altitude and at the third speed prior to a third time, wherein the third time follows the second time;   selecting a fourth rotational speed and a fourth orientation for the first propulsion motor based at least in part on the second net propulsion force; and   causing the first propulsion motor to operate at the fourth rotational speed and a fourth orientation at the third time.   
     
     
         16 . The method of  claim 8 , wherein determining the first net propulsion force comprises:
 determining a wind velocity within a vicinity of the aerial vehicle prior to the first time;   calculating the first net propulsion force based at least in part on the wind velocity and at least one of the first angular orientation, the first course, the first altitude and the first speed.   
     
     
         17 . The method of  claim 8 , wherein the aerial vehicle comprises at least one sensor, and
 wherein determining that the second propulsion motor is ineffective at the first time comprises:   determining, by the at least one sensor, at least one of an electric current flowing to or from the second propulsion motor or a voltage drop across the second propulsion motor at the first time; and   determining that the at least one of the electric current or the voltage drop is above or below a predetermined threshold at the first time.   
     
     
         18 . The method of  claim 8 , wherein the aerial vehicle comprises at least one sensor, and
 wherein determining that the second propulsion motor is ineffective at the first time comprises:   determining, by the at least one sensor, a rotational speed of the second propulsion motor at the first time; and   determining that the rotational speed of the second propulsion motor at the first time is less than the second rotational speed.   
     
     
         19 . The method of  claim 8 , wherein the aerial vehicle comprises at least one sensor, and
 wherein determining that the second propulsion motor is ineffective at the first time comprises:   determining, by the at least one sensor, a temperature associated with the second propulsion motor at the first time; and   determining that the temperature associated with the second propulsion motor exceeds a predetermined threshold at the first time.   
     
     
         20 . The method of  claim 8 , wherein the aerial vehicle comprises at least one sensor, and
 wherein determining that the second propulsion motor is ineffective at the first time comprises:   capturing, by the at least one sensor, at least one of imaging data or acoustic data at the first time; and   detecting at least one abnormal condition of the second propulsion motor at the first time based at least in part on the at least one of the imaging data or the acoustic data.