Propeller impact detection and force reduction

1. A system, comprising:

a rotor; and

a motor controller including:

a rotor strike detector configured to detect the rotor being struck based at least in part on a comparison between a commanded control signal and an adaptive control signal, wherein the adaptive control signal is associated with controlling the rotor and the adaptive control signal varies based at least in part on the commanded control signal and state information associated with the rotor; and

a drive and control unit configured to, in response to detecting the rotor strike, adjust a control signal to the rotor to reduce a speed of rotation of the rotor and to reduce a striking force applied to an object being struck by the rotor including by:

in response to an altitude associated with the system exceeding an altitude threshold, at least temporarily adjusting the control signal to the rotor to reduce the speed of rotation of the rotor and the striking force; and

in response to the altitude not exceeding the altitude threshold, adjusting the control signal to the rotor to reduce the speed of rotation of the rotor and the striking force, at least until one or more of the following occurs: a reset or a part replacement.

2. The system recited in claim 1 , wherein the motor controller is further configured to compare the commanded control signal and the adaptive control signal including by:

determining a reference signal based at least in part on the commanded control signal;

determining a degree to which the adaptive control signal, which includes a sinusoidal signal, deviates from the reference signal;

comparing the degree against a detection threshold; and

in response to the degree exceeding the detection threshold, declaring that the rotor strike has been detected.

3. The system recited in claim 1 , wherein the motor controller is further configured to compare the commanded control signal and the adaptive control signal including by:

determining a reference signal based at least in part on the commanded control signal, wherein the reference signal includes a measurement threshold;

determining a degree to which the adaptive control signal, which includes a sinusoidal signal, deviates from the reference signal;

comparing the degree against a detection threshold; and

in response to the degree exceeding the detection threshold, declaring that the rotor strike has been detected.

4. The system recited in claim 1 , wherein the motor controller is further configured to compare the commanded control signal and the adaptive control signal including by:

determining a reference signal based at least in part on the commanded control signal, wherein the reference signal includes a sinusoidal reference signal;

determining a degree to which the adaptive control signal, which includes a sinusoidal signal, deviates from the reference signal;

comparing the degree against a detection threshold; and

in response to the degree exceeding the detection threshold, declaring that the rotor strike has been detected.

5. The system recited in claim 1 , wherein adjusting the control signal to the rotor in order to reduce the striking force includes:

in response to detecting the rotor strike, using an electrical connector to electrically disconnect the adaptive control signal from a rotor input signal; and

in response to electrically disconnecting the adaptive control signal from the rotor input signal, using a pull resistor to set the rotor input signal to a known value associated with reducing the striking force associated with the rotor.

6. The system recited in claim 1 , wherein adjusting the control signal to the rotor in order to reduce the striking force includes:

in response to detecting the rotor strike, opening a power switch in a switched converter, wherein the power switch is connected to a power supply at one end and the adaptive control signal at the other end such that opening the power switch electrically disconnects the adaptive control signal from the power supply; and

in response to detecting the rotor strike, closing a ground switch in the switched converter, wherein the ground switch is connected to ground at one end and the adaptive control signal at the other end such that closing the power switch electrically connects the adaptive control signal to ground.

7. The system recited in claim 1 , wherein adjusting the control signal to the rotor in order to reduce the striking force includes:

in response to detecting the rotor strike, opening a power switch in a switched converter, wherein the power switch is connected to a power supply at one end and the adaptive control signal at the other end such that opening the power switch electrically disconnects the adaptive control signal from the power supply; and

in response to detecting the rotor strike, opening a ground switch in the switched converter, wherein the ground switch is connected to ground at one end and the adaptive control signal at the other end such that opening the power switch electrically disconnects the adaptive control signal from ground.

8. The system recited in claim 1 , wherein adjusting the control signal to the rotor in order to reduce the striking force includes:

in response to detecting the rotor strike, obtaining the altitude associated with an aircraft;

comparing the altitude against the altitude threshold.

9. The system recited in claim 1 , wherein adjusting the control signal to the rotor in order to reduce the striking force includes:

in response to detecting the rotor strike, obtaining the altitude associated with an aircraft;

comparing the altitude against the altitude threshold; and

at least temporarily adjusting the control signal to the rotor in order to reduce the striking force associated with the rotor includes permitting the rotor to restart in response to a pilot restart instruction without a reset prior to the pilot restart instruction or a part replacement prior to the pilot restart instruction.

10. The system recited in claim 1 , wherein adjusting the control signal to the rotor in order to reduce the striking force includes:

in response to detecting the rotor strike, obtaining the altitude associated with the system;

comparing the altitude against a higher altitude threshold and a lower altitude threshold;

in response to the altitude not exceeding the lower altitude threshold, adjusting the control signal to the rotor in order to reduce the striking force associated with the rotor; and

in response to the altitude exceeding the higher altitude threshold, adjusting the control signal to the rotor in order to reduce the striking force associated with the rotor, wherein in response to the altitude exceeding the lower altitude threshold and not exceeding the higher altitude threshold, the striking force associated with the rotor is not reduced.

11. A method, comprising:

detecting a rotor being struck based at least in part on a comparison between a commanded control signal and an adaptive control signal, wherein the adaptive control signal is associated with controlling the rotor and the adaptive control signal varies based at least in part on the commanded control signal and state information associated with the rotor; and

in response to detecting the rotor strike, adjusting a control signal to the rotor to reduce a speed of rotation of the rotor and to reduce a striking force applied to an object being struck by the rotor including by:

in response to an altitude associated with an aircraft exceeding an altitude threshold, at least temporarily adjusting the control signal to the rotor to reduce the speed of rotation of the rotor and the striking force; and

in response to the altitude not exceeding the altitude threshold, adjusting the control signal to the rotor to reduce the speed of rotation of the rotor and the striking force, at least until one or more of the following occurs: a reset or a part replacement.

12. The method recited in claim 11 , further comprising comparing the commanded control signal and the adaptive control signal including by:

determining a reference signal based at least in part on the commanded control signal;

determining a degree to which the adaptive control signal, which includes a sinusoidal signal, deviates from the reference signal;

comparing the degree against a detection threshold; and

in response to the degree exceeding the detection threshold, declaring that the rotor strike has been detected.

13. The method recited in claim 11 , further comprising comparing the commanded control signal and the adaptive control signal including by:

determining a reference signal based at least in part on the commanded control signal, wherein the reference signal includes a measurement threshold;

determining a degree to which the adaptive control signal, which includes a sinusoidal signal, deviates from the reference signal;

comparing the degree against a detection threshold; and

in response to the degree exceeding the detection threshold, declaring that the rotor strike has been detected.

14. The method recited in claim 11 , further comprising comparing the commanded control signal and the adaptive control signal including by:

determining a reference signal based at least in part on the commanded control signal, wherein the reference signal includes a sinusoidal reference signal;

determining a degree to which the adaptive control signal, which includes a sinusoidal signal, deviates from the reference signal;

comparing the degree against a detection threshold; and

in response to the degree exceeding the detection threshold, declaring that the rotor strike has been detected.

15. The method recited in claim 11 , wherein adjusting the control signal to the rotor in order to reduce the striking force includes:

in response to detecting the rotor strike, using an electrical connector to electrically disconnect the adaptive control signal from a rotor input signal; and

in response to electrically disconnecting the adaptive control signal from the rotor input signal, using a pull resistor to set the rotor input signal to a known value associated with reducing the striking force associated with the rotor.

16. The method recited in claim 11 , wherein adjusting the control signal to the rotor in order to reduce the striking force includes:

in response to detecting the rotor strike, opening a power switch in a switched converter, wherein the power switch is connected to a power supply at one end and the adaptive control signal at the other end such that opening the power switch electrically disconnects the adaptive control signal from the power supply; and

in response to detecting the rotor strike, closing a ground switch in the switched converter, wherein the ground switch is connected to ground at one end and the adaptive control signal at the other end such that closing the power switch electrically connects the adaptive control signal to ground.

17. The method recited in claim 11 , wherein adjusting the control signal to the rotor in order to reduce the striking force includes:

in response to detecting the rotor strike, opening a power switch in a switched converter, wherein the power switch is connected to a power supply at one end and the adaptive control signal at the other end such that opening the power switch electrically disconnects the adaptive control signal from the power supply; and

in response to detecting the rotor strike, opening a ground switch in the switched converter, wherein the ground switch is connected to ground at one end and the adaptive control signal at the other end such that opening the power switch electrically disconnects the adaptive control signal from ground.

18. The method recited in claim 11 , wherein adjusting the control signal to the rotor in order to reduce the striking force includes:

in response to detecting the rotor strike, obtaining the altitude associated with the aircraft;

comparing the altitude against the altitude threshold.

19. The method recited in claim 11 , wherein adjusting the control signal to the rotor in order to reduce the striking force includes:

in response to detecting the rotor strike, obtaining the altitude associated with the aircraft;

comparing the altitude against the altitude threshold;

at least temporarily adjusting the control signal to the rotor in order to reduce the striking force associated with the rotor includes permitting, the rotor to restart in response to a pilot restart instruction without a reset prior to the pilot restart instruction or a part replacement prior to the pilot restart instruction.

20. A computer program product, the computer program product being embodied in a non-transitory computer readable storage medium and comprising computer instructions for:

detecting a rotor being struck based at least in part on a comparison between a commanded control signal and an adaptive control signal, wherein the adaptive control signal is associated with controlling the rotor and the adaptive control signal varies based at least in part on the commanded control signal and state information associated with the rotor; and

in response to detecting the rotor strike, adjusting a control signal to the rotor to reduce a speed of rotation of the rotor and to reduce a striking force applied to an object being struck by the rotor including by:

in response to an altitude associated with an aircraft exceeding an altitude threshold, at least temporarily adjusting the control signal to the rotor to reduce the speed of rotation of the rotor and the striking force; and

in response to the altitude not exceeding the altitude threshold, adjusting the control signal to the rotor to reduce the speed of rotation of the rotor and the striking force, at least until one or more of the following occurs: a reset or a part replacement.