Intentionally imbalancing propellers for performance and noise-shaping

Patent metadata

Field	Value
Publication number	US-9902490-B2
Application number	US-201715658168-A
Country	US
Kind code	B2
Filing date	Jul 24, 2017
Priority date	Dec 18, 2015
Publication date	Feb 27, 2018
Grant date	Feb 27, 2018

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.

First claim

What is claimed is:

1. A method for operating an aerial vehicle, wherein the method comprises:
identifying information regarding at least one attribute of a mission for the aerial vehicle having a first motor and a second motor;
rotatably coupling a first propeller to a first shaft of the first motor, wherein the first propeller is statically balanced and dynamically balanced;
predicting a noise to be emitted during a rotation of a second propeller above a critical speed of the second propeller, wherein the second 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 second propeller, wherein the modified second propeller is at least one of statically imbalanced or dynamically imbalanced after executing the modification;
rotating the modified second propeller above a critical speed of the modified second propeller;
determining that a noise emitted during the rotation of the modified second propeller above the critical speed is consistent with the at least one attribute of the mission;
rotatably coupling the modified second propeller to a second shaft of the second motor; and
causing the aerial vehicle to perform the mission,
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.

2. The method of claim 1 , wherein a first center of mass is aligned along an axis of rotation along the first shaft,
wherein centrifugal forces acting upon each of a first plurality of blades of the first propeller are equal to and counteract one another when the first propeller is rotated above the critical speed of the first propeller,
wherein a second center of mass of the modified second propeller is not aligned along an axis of rotation of the second shaft, and
wherein centrifugal forces acting upon each of a second plurality of blades of the modified second propeller are not equal to or do not counteract one another when the modified second propeller is rotated above the critical speed of the modified second propeller.

3. The method of claim 1 , wherein causing the aerial vehicle to perform the emission comprises:
causing a rotation of the first propeller above a critical speed of the first propeller;
determining a position of the aerial vehicle;
determining that the position of the aerial vehicle is within a predetermined range of one of the location of the origin, the location of the destination or the location of the intervening waypoint;
in response to determining that the position of the aerial vehicle is within a predetermined range of one of the location of the origin, the location of the destination or the location of the intervening waypoint,
stopping the rotation of the first propeller; and
causing a rotation of the modified second propeller above the critical speed of the modified second propeller.

4. The method of claim 1 , wherein the second propeller comprises a first blade and a second blade, and wherein executing the modification to the second 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.

5. A method comprising:
prior to an operation of an aerial vehicle, predicting an attribute of the aerial vehicle during the operation, wherein the aerial vehicle comprises a first motor and a second motor;
coupling a first propeller to a first shaft of the first motor, wherein the first propeller is statically balanced and dynamically balanced;
determining a modification to a second propeller based at least in part on the predicted attribute;
modifying the second propeller in accordance with the determined modification, wherein the second propeller is statically balanced and dynamically balanced prior to modifying the second propeller in accordance with the determined modification, and wherein the second propeller is at least one of statically imbalanced or dynamically imbalanced after modifying the second propeller in accordance with the determined modification;
coupling the modified second propeller to a second shaft of the second motor; and
initiating the operation of the aerial vehicle, wherein the operation of the aerial vehicle comprises:
rotating the first propeller above a critical speed at a first time; and
rotating the modified second propeller above a critical speed at a second time.

6. The method of claim 5 , wherein a center of mass of the modified second propeller is not aligned with an axis of rotation of the second shaft after the second propeller has been coupled to the second shaft.

7. The method of claim 5 , 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.

8. The method of claim 5 , further comprising:
prior to modifying the second propeller,
rotating the second propeller above the critical speed;
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 desired based at least in part on the predicted attribute of the aerial vehicle during the operation; and
determining the modification based at least in part on the first frequency spectrum or the first sound pressure level.

9. The method of claim 8 , 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 desired 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 determined based at least in part

Assignees

• Amazon Tech Inc

Inventors

• Beckman Brian C
• Ko Allan

Classifications

• B64U2201/10

  autonomous, i.e. by navigating independently from ground or air stations, e.g. by using inertial navigation systems [INS] · CPC title

• G01C21/00

  Navigation; Navigational instruments not provided for in groups G01C1/00 - G01C19/00 (measuring distance traversed on the ground by a vehicle G01C22/00; control of position, course, altitude or attitude of vehicles G05D1/00; traffic control systems for road vehicles involving transmission of navigation instructions to the vehicle G08G1/0968) · CPC title

• B64C2201/108

  Operations & Transport · mapped topic

• B64C39/024

  of the remote controlled vehicle type, i.e. RPV · CPC title

• G05D13/00

  Control of linear speed; Control of angular speed; Control of acceleration or deceleration, e.g. of a prime mover · CPC title