# When I turn off a servo how much do torque I need to rotate it?

I'm designing the actuation of a throttle for an engine.I thought to put a servo to move the plate.

Very interesting are the smart servos used for the robotics(for example dynamixel AX-12W http://www.trossenrobotics.com/p/ax-12w-dynamixel-robot-servo.aspx).

I need that when I push the shutdown button(for emergency) the plate of the throttle returns to the idle position.The throttle already has two return springs.

I have some ideas to calculate the right reduction to move the plate when the servo is powered on but where I can find the torque value that i need to rotate the servo when it's powered off?

If I knew that value I'll know the right spring constant.

Thanks

• Ask the manufacturer - but not all servos are safe to be back-driven, you may have to use stepper motors. – pjc50 Jan 9 '17 at 15:45

If you want to attempt your own throttle control system you can buy vehicle rated throttle servos (for cruise control) very cheaply (~$50-150 new) which starts right about the same price as the Dynamixel servo alone, but already has the cable pulls attached. You can get used cruise control servos for <$20 on Ebay, so why not use the real thing.