Rotor noise reduction using signal processing

1. A system, comprising:

a memory; and

a processor coupled to the memory and configured to:

receive a takeoff location and a landing location for an autonomous vertical takeoff and landing (VTOL) vehicle that includes a plurality of rotors;

determine an autonomous and noise-reduced flight trajectory for the autonomous VTOL vehicle based at least in part on the takeoff location, the landing location, a jerk function, and a noise function, including by minimizing the jerk function and minimizing the noise function;

determine a set of one or more desired forces or moments for the autonomous VTOL vehicle based at least in part on autonomous and noise-reduced flight trajectory; and

determine a plurality of motor control signals for the plurality of rotors based at least in part on the set of one or more desired forces or moments, wherein:

the plurality of rotors includes a first phase-locked rotor and a second phase-locked rotor; and

determining the plurality of motor control signals for the plurality of rotors includes determining a first phase-locked motor control signal for the first phase-locked rotor and a second phase-locked motor control signal for the second phase-locked rotor, wherein the first phase-locked motor control signal and the second phase-locked motor control signal cause the first phase-locked rotor and the second phase-locked rotor to respectively rotate at a fixed phase difference.

2. The system recited in claim 1 , wherein:

the autonomous VTOL vehicle includes an overwater vehicle that includes a float having a top surface;

the plurality of rotors includes an inboard rotor that is disposed on the top surface of the float; and

the plurality of rotors includes an outboard rotor that is disposed on a distal end of a boom that extends outward from a fuselage.

3. The system recited in claim 1 , wherein the autonomous and noise-reduced flight trajectory has one or more of the following properties compared to an autonomous flight trajectory that is determined without using the noise function: a longer trajectory, a longer flight duration, a lower maximum speed, or a higher cruising altitude.

4. The system recited in claim 1 , wherein:

the plurality of rotors includes a first rotor and a second rotor; and

determining the plurality of motor control signals for the plurality of rotors includes determining a first deconflicted motor control signal for the first rotor and a second deconflicted motor control signal for the second rotor, wherein the first deconflicted motor control signal and the second deconflicted motor control signal cause the first rotor and the second rotor to respectively rotate at a frequency difference that exceeds a threshold.

5. The system recited in claim 1 , wherein:

the plurality of rotors includes a first rotor and a second rotor;

determining the plurality of motor control signals for the plurality of rotors includes determining a first deconflicted motor control signal for the first rotor and a second deconflicted motor control signal for the second rotor, wherein the first deconflicted motor control signal and the second deconflicted motor control signal cause the first rotor and the second rotor to respectively rotate at a frequency difference that exceeds a threshold; and

the first rotor and the second rotor include a first center inboard rotor and a second center inboard rotor.

6. The system recited in claim 1 , wherein:

the plurality of rotors includes a first rotor and a second rotor; and

determining the plurality of motor control signals for the plurality of rotors includes determining a first deconflicted motor control signal for the first rotor and a second deconflicted motor control signal for the second rotor, wherein:

the first deconflicted motor control signal and the second deconflicted motor control signal cause the first rotor and the second rotor to respectively rotate at a frequency difference that exceeds a threshold; and

determining the first deconflicted motor control signal for the first rotor and the second deconflicted motor control signal for the second rotor includes:

receiving a first raw motor control signal for the first rotor and a second raw motor control signal for the second rotor;

comparing the first raw motor control signal and the second raw motor control signal; and

adjusting at least one of the first raw motor control signal or the second raw motor control signal for a second of the first raw motor control signal and the second raw motor control signal where the first rotor and the second rotor would not respectively rotate at a frequency difference that exceeds the threshold.

7. The system recited in claim 1 , wherein the first phase-locked rotor and the second phase-locked rotor include a first center inboard rotor and a second center inboard rotor.

8. The system recited in claim 1 , wherein determining the plurality of motor control signals for the plurality of rotors includes:

determining whether a control margin exceeds a threshold;

in the event it is determined that the control margin exceeds the threshold, determining at least one noise-reduced motor control signal for the plurality of rotors; and

in the event it is determined that the control margin does not exceed the threshold, determining a non-noise-reduced motor control signal for each of the plurality of rotors.

9. The system recited in claim 1 , wherein determining the plurality of motor control signals for the plurality of rotors includes:

determining whether a moving window of past motor control signals satisfies a steady state criteria;

in the event it is determined that the moving window of past motor control signals satisfies the steady state criteria, determining at least one noise-reduced motor control signal for the plurality of rotors; and

in the event it is determined that the moving window of past motor control signals does not satisfy the steady state criteria, determining a non-noise-reduced motor control signal for each of the plurality of rotors.

10. A method, comprising:

receiving a takeoff location and a landing location for an autonomous vertical takeoff and landing (VTOL) vehicle that includes a plurality of rotors;

determining an autonomous and noise-reduced flight trajectory for the autonomous VTOL vehicle based at least in part on the takeoff location, the landing location, a jerk function, and a noise function, including by minimizing the jerk function and minimizing the noise function;

determining a set of one or more desired forces or moments for the autonomous VTOL vehicle based at least in part on autonomous and noise-reduced flight trajectory; and

determining a plurality of motor control signals for the plurality of rotors based at least in part on the set of one or more desired forces or moments, wherein:

the plurality of rotors includes a first phase-locked rotor and a second phase-locked rotor; and

determining the plurality of motor control signals for the plurality of rotors includes determining a first phase-locked motor control signal for the first phase-locked rotor and a second phase-locked motor control signal for the second phase-locked rotor, wherein the first phase-locked motor control signal and the second phase-locked motor control signal cause the first phase-locked rotor and the second phase-locked rotor to respectively rotate at a fixed phase difference.

11. The method recited in claim 10 , wherein:

the autonomous VTOL vehicle includes an overwater vehicle that includes a float having a top surface;

the plurality of rotors includes an inboard rotor that is disposed on the top surface of the float; and

the plurality of rotors includes an outboard rotor that is disposed on a distal end of a boom that extends outward from a fuselage.

12. The method recited in claim 10 , wherein the autonomous and noise-reduced flight trajectory has one or more of the following properties compared to an autonomous flight trajectory that is determined without using the noise function: a longer trajectory, a longer flight duration, a lower maximum speed, or a higher cruising altitude.

13. The method recited in claim 10 , wherein:

the plurality of rotors includes a first rotor and a second rotor; and

determining the plurality of motor control signals for the plurality of rotors includes determining a first deconflicted motor control signal for the first rotor and a second deconflicted motor control signal for the second rotor, wherein the first deconflicted motor control signal and the second deconflicted motor control signal cause the first rotor and the second rotor to respectively rotate at a frequency difference that exceeds a threshold.

14. The method recited in claim 10 , wherein:

the plurality of rotors includes a first rotor and a second rotor;

determining the plurality of motor control signals for the plurality of rotors includes determining a first deconflicted motor control signal for the first rotor and a second deconflicted motor control signal for the second rotor, wherein the first deconflicted motor control signal and the second deconflicted motor control signal cause the first rotor and the second rotor to respectively rotate at a frequency difference that exceeds a threshold; and

the first rotor and the second rotor include a first center inboard rotor and a second center inboard rotor.

15. The method recited in claim 10 , wherein:

the plurality of rotors includes a first rotor and a second rotor; and

determining the plurality of motor control signals for the plurality of rotors includes determining a first deconflicted motor control signal for the first rotor and a second deconflicted motor control signal for the second rotor, wherein:

the first deconflicted motor control signal and the second deconflicted motor control signal cause the first rotor and the second rotor to respectively rotate at a frequency difference that exceeds a threshold; and

determining the first deconflicted motor control signal for the first rotor and the second deconflicted motor control signal for the second rotor includes:

receiving a first raw motor control signal for the first rotor and a second raw motor control signal for the second rotor;

comparing the first raw motor control signal and the second raw motor control signal; and

adjusting at least one of the first raw motor control signal or the second raw motor control signal for a second of the first raw motor control signal and the second raw motor control signal where the first rotor and the second rotor would not respectively rotate at a frequency difference that exceeds the threshold.

16. The method recited in claim 10 , wherein the first phase-locked rotor and the second phase-locked rotor include a first center inboard rotor and a second center inboard rotor.

17. The method recited in claim 10 , wherein determining the plurality of motor control signals for the plurality of rotors includes:

determining whether a control margin exceeds a threshold;

in the event it is determined that the control margin exceeds the threshold, determining at least one noise-reduced motor control signal for the plurality of rotors; and

in the event it is determined that the control margin does not exceed the threshold, determining a non-noise-reduced motor control signal for each of the plurality of rotors.

18. The method recited in claim 10 , wherein determining the plurality of motor control signals for the plurality of rotors includes:

determining whether a moving window of past motor control signals satisfies a steady state criteria;

in the event it is determined that the moving window of past motor control signals satisfies the steady state criteria, determining at least one noise-reduced motor control signal for the plurality of rotors; and

in the event it is determined that the moving window of past motor control signals does not satisfy the steady state criteria, determining a non-noise-reduced motor control signal for each of the plurality of rotors.