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An actuator, comprises a housing, a first prime mover for producing rotary motion, a first gearbox arranged to convert in use the rotary motion from the first prime mover into rotary motion having higher torque and lower speed. The first gearbox comprises a casing mounted for rotation relative to th

An actuator, comprises a housing, a first prime mover for producing rotary motion, a first gearbox arranged to convert in use the rotary motion from the first prime mover into rotary motion having higher torque and lower speed. The first gearbox comprises a casing mounted for rotation relative to the housing of the actuator and a second gearbox arranged to convert rotary motion of the casing of the first gearbox into rotary motion having lower torque and higher speed. A brake is arranged to act on the rotary motion having lower torque and higher speed from the second gearbox. In use when the first gearbox is not jammed, the brake may be applied to resist relative rotation between the casing of the first gearbox and the housing of the actuator. When the first gearbox is jammed, the brake may be released thereby allowing the casing of the first gearbox to rotate relative to the housing of the actuator. The actuator may thereby be jam-tolerant. A second motor may also be provided.

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1. An actuator, wherein the actuator comprises a housing,a first prime mover for producing rotary motion,a first gearbox arranged to convert in use the rotary motion from the first prime mover into rotary motion having higher torque and lower speed, the first gearbox comprising a casing mounted for

1. An actuator, wherein the actuator comprises a housing,a first prime mover for producing rotary motion,a first gearbox arranged to convert in use the rotary motion from the first prime mover into rotary motion having higher torque and lower speed, the first gearbox comprising a casing mounted for rotation relative to the housing of the actuator,a second gearbox arranged to convert rotary motion of the casing of the first gearbox into rotary motion having lower torque and higher speed, anda brake arranged to act on the rotary motion having lower torque and higher speed from the second gearbox, whereby in use(i) when the first gearbox is not jammed, the brake may be applied to resist relative rotation between the casing of the first gearbox and the housing of the actuator and(ii) when the first gearbox is jammed, the brake may be released thereby allowing the casing of the first gearbox to rotate relative to the housing of the actuator. 2. An actuator according to claim 1, wherein the first prime mover is fixed relative to the housing. 3. An actuator according to claim 1, wherein the first gearbox has a gear ratio higher than 30:1. 4. An actuator according to claim 1, wherein the second gearbox has a gear ratio lower than the first gearbox. 5. An actuator according to claim 1, wherein the actuator is so configured that the output of the first gearbox is able, in use, to produce output rotation over a range of at least +/−180 degrees. 6. An actuator according to claim 1, wherein the actuator is back-driveable in the event of the first gearbox jamming. 7. An actuator according to claim 1, wherein the actuator includes a damping mechanism arranged such that, at least when the first gearbox is jammed, the motion of the actuator is damped. 8. An actuator according to claim 1, wherein the actuator may include a second prime mover for producing rotary motion, the second prime mover being associated with the second gearbox. 9. An actuator according to claim 8, wherein the actuator includes a jamming mechanism, which is able in use to jam the first gearbox. 10. An actuator according to claim 1, wherein the actuator includes a control unit arranged to detect jamming of the first gearbox. 11. A landing gear assembly including a landing gear leg for supporting at least one wheel of an aircraft, and an actuator arranged to steer the landing gear leg, the actuator being an actuator according to claim 1. 12. An aircraft including an aircraft component and an actuator arranged to move the aircraft component, the actuator being an actuator according to claim 1. 13. A kit, comprising: parts for manufacturing an actuator, said actuator comprisinga housing,a first prime mover for producing rotary motion,a first gearbox arranged to convert in use the rotary motion from the first prime mover into rotary motion having higher torque and lower speed, the first gearbox comprising a casing mounted for rotation relative to the housing of the actuator,a second gearbox arranged to convert rotary motion of the casing of the first gearbox into the rotary motion having lower torque and higher speed, anda brake arranged to act on the rotary motion having lower torque and higher speed from the second gearbox, whereby in use(i) when the first gearbox is not jammed, the brake may be applied to resist relative rotation between the casing of the first gearbox and the housing of the actuator and(ii) when the first gearbox is jammed, the brake may be released thereby allowing the casing of the first gearbox to rotate relative to the housing of the actuator. 14. A method of moving a component, wherein the method comprises the steps of providing input rotary motion having a first torque to a first gearbox,applying a counter-torque to substantially prevent rotary motion of the whole of the first gearbox, the counter-torque being applied via a second gearbox,the first gearbox outputting rotary motion having a second torque, higher than the first torque, which causes the component to move, andthen, after jamming of the first gearbox,releasing the counter-torque applied via the second gearbox, thereby allowing the whole of the first gearbox to rotate, and thereby preventing the jamming of the first gearbox from precluding movement of the component. 15. A method according to claim 14, wherein the counter-torque is applied by means of a brake applied at the input to the second gearbox, the output of the second gearbox providing a counter-torque having a higher torque as a result of the gear ratio of the second gearbox. 16. A method according to claim 14, wherein the method includes a step, performed after jamming of the first gearbox, of moving the component by means other than via the first or second gearboxes. 17. A method according to claim 14, wherein the method includes steps of monitoring for jamming of the first gearbox, detecting jamming of the first gearbox and then consequently causing the counter-torque applied via the second gearbox to be released.