Variable torque electric motor assembly

1. An actuator assembly comprising:

an electric motor including a rotor assembly and a stator assembly configured to be actuated to cause the rotor assembly to rotate based on an amount of magnetic flux in the rotor assembly;

a controllable magnetic device coupled to the rotor assembly;

an actuator coupled to the rotor assembly; and

a controller configured to apply electric current to the controllable magnetic device to adjust an amount of torque provided by the electric motor by adjusting the magnetic flux in the rotor assembly;

wherein the electric motor is configured to generate an amount of torque that is less than or equal to a maximum amount of torque, and the controllable magnetic device is configured to increase the maximum amount of torque based on a change in a condition that affects the electric motor.

2. The actuator assembly of claim 1 , wherein the controller includes a field coupler coupled to the rotatable member and configured to rotate with the rotor assembly.

3. The actuator assembly of claim 2 , wherein the field coupler is configured to be energized by stationary windings.

4. The actuator assembly of claim 2 , wherein the controller includes a rectifier device configured to convert alternating current generated by the field coupler to direct current and apply the direct current to the controllable magnetic device.

5. The actuator assembly of claim 1 , wherein the controllable magnetic device includes one or more windings coupled to the rotatable member.

6. The actuator assembly of claim 1 , wherein the rotor assembly includes a permanent magnet.

7. The actuator assembly of claim 6 , wherein the rotor assembly and the stator assembly form at least part of a brushless direct current (DC) motor.

8. An actuator assembly comprising:

an electric motor including a rotor assembly and a stator assembly configured to be actuated to cause the rotor assembly to rotate based on an amount of magnetic flux in the rotor assembly;

a controllable magnetic device coupled to the rotor assembly;

an actuator coupled to the rotor assembly; and

a controller configured to apply electric current to the controllable magnetic device to adjust an amount of torque provided by the electric motor by adjusting the magnetic flux in the rotor assembly;

wherein the controller is configured to apply the electric current in a first direction to increase the amount of torque by increasing the magnetic flux in the rotor assembly.

9. The actuator assembly of claim 8 , wherein the controller is configured to apply the electric current in a second direction to decrease the amount of torque by decreasing the magnetic flux in the rotor assembly.

10. A method of controlling an actuator assembly comprising:

actuating an electric motor by applying a first electric current to a stator assembly to cause rotation of a rotor assembly, the rotor assembly configured to rotate based on an amount of magnetic flux in the rotor assembly;

causing movement of an actuator coupled to the rotor assembly; and

applying a second electric current to a controllable magnetic device coupled to the rotor assembly, the second electric current causing an amount of torque provided by the electric motor to change by adjusting the magnetic flux in the rotor assembly;

wherein the electric motor is configured to generate an amount of torque that is less than or equal to a maximum amount of torque, and the controllable magnetic device is configured to increase the maximum amount of torque based on a change in a condition that affects the electric motor.

11. The method of claim 10 , wherein the first electric current is applied in a first direction to increase the amount of torque by increasing the magnetic flux in the rotor assembly.

12. The method of claim 10 , wherein the first electric current is applied in a second direction to decrease the amount of torque by decreasing the magnetic flux in the rotor assembly.

13. The method of claim 10 , wherein the second electric current is applied via a field coupler coupled to the rotatable member and configured to rotate with the rotor assembly.

14. The method of claim 13 , wherein the field coupler is configured to be energized by stationary windings.

15. The method of claim 13 , wherein the field coupler is connected to a rectifier device configured to convert alternating current generated by the field coupler to direct current and apply the direct current to the controllable magnetic device.

16. The method of claim 10 , wherein the controllable magnetic device includes one or more windings coupled to the rotatable member.

17. The method of claim 10 , wherein the rotor assembly includes a permanent magnet.

18. The method of claim 17 , wherein the rotor assembly and the stator assembly form at least part of a brushless direct current (DC) motor.