bearing or clutch?

[cott]

I have an application where a spool is connected to a small dc motor. The spool must be able to freewheel when the motor is not on(i.e. to allow cable to run freely off the spool). When the motor is on, it shall engauge the spool and turn it in the opposite direction (i.e. rewind the cable).

The application would require less than 1 ft.lb of torque. Any suggestion for a low cost simple coupling device and possible suppliers?

 

[israelkk]

Electrically "disconnect" the motor terminals and let the motor run freely. This way the motor will not create a resistance back EMF current and torque.

 

[cott]

Thanks Israelkk, but this is connected to a gearmotor and there is too much drag if we just disconnect the motor terminals.

 

[NuclearNerd]

Stock Drive Products have a lot of small electromagnetic clutches which could work for you. If you would rather a mechanical solution, assuming the overrun is only one direction and you can afford some drag, you could also consider thomson wrap-spring clutches.

http://www.sdp-si.com/eStore/CoverPg/Brakes.htm

http://www.thomsonlinear.com/website/com/eng/products/clutches_and_brakes/wrap_spring_clutches.php