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I am using servo and stepper motors for the first time, and have been searching for a solution to this basic problem:

I want to drive a shaft with a motor, whereby this shaft also has a ‘neutral’ state that can be switched on/off with a microcontroller. In this neutral state the shaft should spin freely, without any friction or resting torque from the motor.

This is any extremely low RPM application, so a precisely balanced solution is not needed, however a low weight/volume solution is preferable. I am currently using a small servo (35 x 16.9 x 32mm) with a max torque of 4.2kg/cm.

The simplest solution I could think of was to build a primitive clutch, whereby one or more solenoids bring a plate that is attached to the motor into contact with a plate that is attached to the shaft. If there is an existing off-the-shelf solution or alternative mechanism that anyone can suggest I would be very grateful to hear your thoughts.

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    \$\begingroup\$ I think, for this situation, I'd be more tempted to make a primitive dog clutch, rather than a primitive plate clutch, like you're describing. Releases just as well, but gives a positive lock when engaging, and requires less "holding force" to maintain torque through it. \$\endgroup\$ – Robherc KV5ROB Apr 25 '17 at 1:15
  • \$\begingroup\$ A hysteresis clutch works well. magtrol.com/brakesandclutches/hysteresis_clutches.html \$\endgroup\$ – Trevor_G Apr 25 '17 at 2:00
  • \$\begingroup\$ Thanks @RobhercKV5ROB for those great suggestions and links; will check them out! \$\endgroup\$ – George Ellis Apr 25 '17 at 5:48
  • \$\begingroup\$ Thanks @Trevor for those great suggestions and links; will check them out! \$\endgroup\$ – George Ellis Apr 25 '17 at 5:49
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I found this website that sells small electric clutches. Industrial Cluctch

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  • \$\begingroup\$ Thanks very much for that link! Your suggested 'Electric clutch' description is a great search term. I also found similar items described as magnetic clutches and link 'electromagnetic clutches' Thanks again! \$\endgroup\$ – George Ellis Apr 25 '17 at 5:46
  • \$\begingroup\$ Glad I could help. \$\endgroup\$ – Dan_LXI Apr 26 '17 at 3:15

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