Operating aerial vehicles with intentionally imbalanced propellers

• US 10,214,279 B2
• Filed: 02/23/2018
• Issued: 02/26/2019
• Est. Priority Date: 12/18/2015
• Status: Active Grant

• Current Assignee: Amazon Technologies, Inc. (Amazon.com, Inc.)
• Original Assignee: Amazon Technologies, Inc. (Amazon.com, Inc.)
• Inventors: Beckman, Brian C., Ko, Allan
• Primary Examiner(s): Figueroa, Jaime
• Application Number:
  US15/904,014
• Publication Number:
  US 20180186444A1
• Time in Patent Office: 368 Days
• Field of Search: 701 1, 701 5
• CPC Class Codes: B64C 11/00 Propellers, e.g. of ducted type; Features common to propellers and rotors for rotorcraft
• CPC Class Codes: B64C 11/20 Constructional features
• CPC Class Codes: B64C 2230/14 achieving noise reductions
• CPC Class Codes: B64C 27/08 with two or more rotors
• CPC Class Codes: B64C 27/32 Rotors
• CPC Class Codes: B64C 27/473 Constructional features
• CPC Class Codes: B64C 39/024 of the remote controlled vehicle type, i.e. RPV
• CPC Class Codes: B64U 10/10 Rotorcrafts
• CPC Class Codes: B64U 10/13 Flying platforms
• CPC Class Codes: B64U 10/14 with four distinct rotor axes, e.g. quadcopters
• CPC Class Codes: B64U 20/20 for noise reduction
• CPC Class Codes: B64U 2101/60 for transporting passengers; for transporting goods other than weapons
• CPC Class Codes: B64U 2101/64 for parcel delivery or retrieval
• CPC Class Codes: B64U 2201/10 autonomous, i.e. by navigating independently from ground or air stations, e.g. by using inertial navigation systems [INS]
• CPC Class Codes: B64U 30/20 Rotors; Rotor supports
• CPC Class Codes: G05D 1/101 specially adapted for aircraft
• CPC Class Codes: G05D 13/00 Control of linear speed; Control of angular speed; Control of acceleration or deceleration, e.g. of a prime mover
• CPC Class Codes: Y02T 50/10 Drag reduction

Abstract

Aerial vehicles may be operated with discrete sets of propellers, which may be selected for a specific purpose or on a specific basis. The discrete sets of propellers may be operated separately or in tandem with one another, and at varying power levels. For example, a set of propellers may be selected to optimize the thrust, lift, maneuverability or efficiency of an aerial vehicle based on a position or other operational characteristic of the aerial vehicle, or an environmental condition encountered by the aerial vehicle. At least one of the propellers may be statically or dynamically imbalanced, such that the propeller emits a predetermined sound during operation. A balanced propeller may be specifically modified to cause the aerial vehicle to emit the predetermined sound by changing one or more parameters of the balanced propeller and causing the balanced propeller to be statically or dynamically imbalanced.

Claims

1. A method comprising:

identifying information regarding at least one attribute of a mission for the aerial vehicle comprising a first motor;

predicting a noise to be emitted during a rotation of a first propeller above a critical speed of the first propeller, wherein the first propeller is statically balanced and dynamically balanced;

determining that at least one of a frequency spectrum of the noise or a sound pressure level of the noise is not consistent with the at least one attribute of the mission;

executing a modification to the first propeller, wherein the modified first propeller is at least one of statically imbalanced or dynamically imbalanced after executing the modification;

rotatably coupling the modified first propeller to a first shaft of the first motor; and

causing the aerial vehicle to perform the mission, wherein the causing the aerial vehicle to perform the mission comprises;

operating the first motor to rotate the modified first propeller above the critical speed of the first propeller during at least a portion of the mission.

2. The method of claim 1, wherein the at least one attribute includes at least one of:

a location of an origin for the mission;

a location of a destination for the mission;

a location of an intervening waypoint between the origin and the destination;

at least one course to be traveled during the performance of the mission;

at least one air speed of the aerial vehicle required during the performance of the mission;

or

a mass of a payload to be carried by the aerial vehicle during the mission.

3. The method of claim 1, wherein a first center of mass of the modified first propeller is not aligned along an axis of rotation of the first shaft, and

wherein centrifugal forces acting upon each of a plurality of blades of the modified first propeller are not equal to or do not counteract one another when the modified first propeller is rotated above the critical speed.

4. The method of claim 1, wherein the first propeller is one of a type of propeller, and

wherein predicting the noise to be emitted during the rotation of the first propeller above the critical speed of the first propeller comprises:

rotatably coupling a second propeller to a second shaft of a second motor, wherein the second propeller is one of the type of propeller, and wherein a critical speed of the second propeller is approximately the critical speed of the first propeller;

operating the first motor to rotate the second propeller above the critical speed;

capturing information regarding at least one sound emitted by the second propeller during rotation of the second propeller above the critical speed by the second motor; and

predicting the noise to be emitted during the rotation of the first propeller above the critical speed of the first propeller based at least in part on the information regarding the at least one sound emitted by the second propeller during the rotation of the second propeller above the critical speed by the second motor.

5. The method of claim 1, wherein the aerial vehicle further comprises a second motor having a second propeller rotatably coupled to a second shaft of the second motor, and

wherein causing the aerial vehicle to perform the emission comprises:

prior to operating the first motor to rotate the modified first propeller above the critical speed of the first propeller during at least the portion of the mission,

operating the second motor to rotate the second propeller above a critical speed of the second propeller;

determining a position of the aerial vehicle;

determining that the position of the aerial vehicle is within a predetermined range of one of a location of an origin for the mission, a location of a destination for the mission or a location of an intervening waypoint between the origin and the destination;

in response to determining that the position of the aerial vehicle is within the predetermined range of one of the location of the origin, the location of the destination or the location of the intervening waypoint,

stopping the operation of the first motor; and

operating the first motor to rotate the modified first propeller above the critical speed of the first propeller.

6. The method of claim 1, wherein the first propeller comprises a first blade and a second blade, and wherein executing the modification to the first propeller comprises at least one of:

removing a core from the second blade;

inserting a slug into the second blade, wherein a density of the slug is greater than a density of a material from which the second blade is formed;

drilling at least a first hole in the second blade;

or

exposing, by a retractable cover disposed within the second blade, at least a second hole in the second blade;

or

modifying at least one of a blade angle or a rake angle of the second blade.

7. A method comprising:

prior to an operation of an aerial vehicle, predicting an attribute of the aerial vehicle during the operation;

selecting a modification to a first propeller based at least in part on the predicted attribute;

modifying the first propeller in accordance with the selected modification, wherein the first propeller is statically balanced and dynamically balanced prior to modifying the first propeller in accordance with the selected modification, and wherein the modified first propeller is at least one of statically imbalanced or dynamically imbalanced;

coupling the modified first propeller to a first shaft of a first motor of the aerial vehicle; and

initiating the operation of the aerial vehicle, wherein the operation of the aerial vehicle comprises;

operating the first motor to rotate the first propeller above a critical speed at a first time.

8. The method of claim 7, wherein a center of mass of the modified first propeller is not aligned with an axis of rotation of the first shaft after the modified first propeller has been coupled to the first shaft.

9. The method of claim 7, wherein the predicted attribute is one of:

a predicted position of the aerial vehicle during the operation;

a predicted course of the aerial vehicle during the operation;

a predicted air speed of the aerial vehicle during the operation;

a predicted environmental condition around the aerial vehicle during the operation;

a predicted operating condition of the aerial vehicle during the operation;

or

a predicted sound emitted by the aerial vehicle during the operation.

10. The method of claim 7, wherein the first propeller is of a type of propeller, and

wherein the method further comprises:

prior to modifying the first propeller,

rotating a second propeller above the critical speed, wherein the second propeller is of the type of propeller;

capturing information regarding a first sound emitted by the second propeller while rotating above the critical speed, wherein the information regarding the first sound comprises at least one of a first frequency spectrum of the first sound or a first sound pressure level of the first sound;

determining that at least one of the first frequency spectrum or the first sound pressure level is not acceptable based at least in part on the predicted attribute of the aerial vehicle during the operation and the information regarding the first sound; and

selecting the modification based at least in part on the first frequency spectrum or the first sound pressure level.

11. The method of claim 10, wherein determining that the at least one of the first frequency spectrum or the first sound pressure level is not acceptable based at least in part on the predicted attribute of the aerial vehicle during the operation comprises:

identifying information regarding a second sound based at least in part on the predicted attribute of the aerial vehicle during the operation, wherein the information regarding the second sound comprises at least one of a second frequency spectrum of the second sound or a second sound pressure level of the second sound, and wherein at least one of the second frequency spectrum or the second sound pressure level is acceptable based at least in part on the predicted attribute of the aerial vehicle during the operation; and

identifying a difference between the first sound and the second sound based at least in part on the information regarding the first sound and the information regarding the second sound,

wherein the modification is selected based at least in part on the difference.

12. The method of claim 10, further comprising:

after modifying the first propeller,

rotating the modified first propeller above the critical speed;

capturing information regarding a second sound emitted by the modified first propeller while rotating above the critical speed, wherein the information regarding the second sound comprises at least one of a second frequency spectrum of the second sound or a second sound pressure level of the second sound; and

determining that at least one of the second frequency spectrum or the second sound pressure level is acceptable based at least in part on the predicted attribute of the aerial vehicle during the operation and the information regarding the second sound,

wherein the modified second propeller is coupled to the second shaft in response to determining that the at least one of the second frequency spectrum or the second sound pressure level is acceptable.

13. The method of claim 7, wherein the first propeller comprises a hub having a mounting bore, a first blade mounted about the hub and a second blade mounted about the hub, and

wherein modifying the first propeller in accordance with the selected modification comprises:

modifying the first blade in accordance with the selected modification; and

not modifying the second blade.

14. The method of claim 13, wherein the selected modification comprises at least one of:

a reduction in at least one of a length or a width;

an increase in mass;

or

a reduction in mass, and

wherein modifying the first blade in accordance with the selected modification comprises at least one of;

reducing at least one of a length or a width of the first blade;

inserting a slug into the first blade at a predetermined distance from the mounting bore of the hub, wherein a density of the slug exceeds a density of a material from which the first blade is formed;

removing a core from the first blade at a predetermined distance from the mounting bore of the hub;

or

opening a hole through at least a portion of the first blade at a predetermined distance from the mounting bore of the hub.

15. The method of claim 7, wherein the operation of the aerial vehicle further comprises:

determining an actual attribute of the aerial vehicle during the operation of the aerial vehicle at approximately the first time;

determining that the actual attribute of the aerial vehicle at approximately the first time is consistent with the predicted attribute at the first time; and

in response to determining that the actual attribute of the aerial vehicle at approximately the first time is consistent with the predicted attribute at the first time,

operating the first motor to rotate the first propeller above the critical speed at the first time.

16. The method of claim 15, wherein the actual attribute is one of:

an actual position of the aerial vehicle at approximately the first time;

an actual course of the aerial vehicle at approximately the first time;

an actual air speed of the aerial vehicle at approximately the first time;

an actual environmental condition around the aerial vehicle at approximately the first time;

an actual operating condition of the aerial vehicle at approximately the first time;

or

an actual sound emitted by the aerial vehicle at approximately the first time.

17. A method comprising:

identifying information regarding an observed noise emitted by a first propeller while rotating above a critical speed, wherein the information regarding the observed noise comprises at least one of a frequency spectrum of the observed noise or a sound pressure level of the observed noise;

identifying information regarding a desired noise to be emitted by a second propeller while operating above the critical speed, wherein the information regarding the desired noise comprises at least one of a frequency spectrum of the desired noise or a sound pressure level of the desired noise, wherein the second propeller and the first propeller are of a common type, and wherein the critical speed is associated with propellers of the common type;

determining that the observed noise is not consistent with the desired noise based at least in part on the information regarding the observed noise and the information regarding the desired noise;

in response to determining that the observed noise is not consistent with the desired noise,

identifying at least one difference between the observed noise and the desired noise;

determining an adjustment to at least one blade of the second propeller based at least in part on the at least one difference;

modifying the at least one blade of the second propeller in accordance with the adjustment;

rotatably coupling the modified second propeller to a motor of an aerial vehicle; and

causing the aerial vehicle to travel at a desired altitude, along a desired course, at a desired air speed or to a desired location,

wherein causing the aerial vehicle to travel at the desired altitude, along the desired course, at the desired air speed or to the desired location comprises;

rotating the modified second propeller above the critical speed.

18. The method of claim 17, wherein the second propeller is statically balanced and dynamically balanced prior to modifying the at least one blade of the second propeller in accordance with the adjustment, and

wherein the modified second propeller is at least one of statically imbalanced or dynamically imbalanced.

19. The method of claim 17, wherein a center of mass of the modified second propeller is not aligned with an axis of rotation of a shaft of the motor of the aerial vehicle with the modified second propeller rotatably coupled to the motor of the aerial vehicle.

20. The method of claim 17, wherein the adjustment is one of:

drilling a hole in the at least one blade of the second propeller;

removing a core from the at least one blade of the second propeller;

inserting a slug into the at least one blade of the second propeller;

changing a rake angle of the at least one blade of the second propeller;

changing a blade angle of the at least one blade of the second propeller;

shortening a length of the at least one blade of the second propeller;

or

reducing a width of the at least one blade of the second propeller.

21. The method of claim 17, wherein identifying the information regarding the desired noise comprises:

identifying at least one noise restriction on the aerial vehicle, wherein the noise restriction on the aerial vehicle is associated with at least one of the desired altitude, the desired course, the desired air speed or the desired location; and

determining the at least one of the frequency spectrum of the desired noise or the sound pressure level of the desired noise based at least in part on the at least one noise restriction.