Limited angle external rotor motor actuator system

1. An actuator system comprising:

an external rotor motor having:

an internal armature configured as a stator having a set of coils wrapped around a set of arms, and

an external permanent magnet rotor having a set of poles configured to rotate less than 90 degrees around the stator;

a drive shaft configured to be rotated by the external rotor motor; and

a drive train connecting the external permanent magnet rotor to the drive shaft, and configured to allow transmission of a first component of rotational motion from the external permanent magnet rotor to the drive shaft and to prevent transmission of a second component of rotational motion from the external permanent magnet rotor to the drive shaft.

2. The actuator system of claim 1 wherein the first component of rotational motion is perpendicular to the second component of rotational motion; and

wherein the drive train comprises a crank arm connected to the external permanent magnet rotor at a motor pin on the external rotor motor, the crank arm defining an elongated crank arm slot configured to have a width substantially that of a diameter of the motor pin in the direction of the first component of rotational motion, and to have a length substantially larger than the diameter of the motor pin in the direction of the second component of rotational motion.

3. The actuator system of claim 2 wherein the first component of rotational motion is perpendicular to a length of the crank arm and is located at the motor pin.

4. The actuator system of claim 2 wherein the motor pin extends from an end surface of the external permanent magnet rotor away from an axis of rotation of the external rotor motor.

5. The actuator system of claim 1 wherein the first component of rotational motion is perpendicular to the second component of rotational motion; and

wherein the drive train comprises:

a drag link pinned to the external permanent magnet rotor; and

a crank arm pinned to the drag link, wherein an angle between the drag link and the crank arm changes as the external permanent magnet rotor rotates.

6. The actuator system of claim 5 wherein angular displacement of the drive shaft about a second axis of rotation will be less than angular displacement the external rotor 30 about a first axis of rotation creating a difference of angular displacement, the difference of angular displacement being a function of relative geometric positions of the external rotor motor, the drive shaft, and the motor pin, and length of the crank arm and drag link.

7. The actuator system of claim 1 wherein the drive train comprises:

a crank arm attached to the drive shaft; and

a drag link forming a first ball-socket joint with the external permanent magnet rotor and a second ball-socket joint with the crank arm, wherein the first ball-socket joint, the second ball-socket joint, and the crank arm are configured to allow transmission of rotational motion from the external permanent magnet rotor to the drive shaft, and wherein the external permanent magnet rotor and the drive shaft have non-parallel axes of rotation.

8. The actuator system of claim 7 wherein angular displacement of the drive shaft about a second axis of rotation will be less than angular displacement the external rotor 30 about a first axis of rotation creating a difference of angular displacement, the difference of angular displacement being a function of relative geometric positions of the external rotor motor and the drive shaft, and length of the crank arm and drag link.

9. The actuator system of claim 1 wherein the internal armature has only four (4) windings and the external permanent magnet rotor has only four (4) poles.

10. The actuator system of claim 1 wherein the drive shaft has a fixed translational position relative to the external rotor motor and is configured to be rotated by the external rotor motor about a fixed axis of rotation extending through the drive shaft.

11. The actuator system of claim 10 wherein the drive train includes an elongated crank arm affixed at one end to the drive shaft and extending away from the drive shaft in a direction perpendicular to the fixed axis of rotation, and wherein the drive train is configured to pivot the crank arm about the fixed axis of rotation to effect rotation of the drive shaft.

12. The actuator system of claim 11 wherein the crank arm includes an elongated slot extending in the direction perpendicular to the fixed axis of rotation, and wherein the external rotor motor includes a pin extending through the slot from an end surface of the external permanent magnet rotor to effect the transmission of the first component of rotational motion while preventing transmission of the second component of rotation motion.

13. A missile, comprising:

a chassis;

one or more fins configured for rotational motion to steer the missile in flight; and

the actuator system of claim 1 , wherein the internal armature of the external rotor motor is rigidly attached to the chassis, and wherein the drive shaft is coupled to the fins to provide the rotational motion of the fins by the rotation of the drive shaft.

14. The missile of claim 13 wherein the fins are directly attached to the drive shaft.

15. A vehicle, comprising:

the actuator system of claim 1 , configured and operative in response to a motor signal to effect a corresponding mechanical flight control action;

a motor controller operative to generate the motor signal in response to a command; and

a vehicle flight controller operative to generate the command to effect control of flight of the vehicle.