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I have the following to wheels that rotate on the same axis:

enter image description here

Assuming that they are stuck together, if I rotate the green one the red one rotates at the same speed and when I stop the green one the red one stops.

I'm looking for the name of the mechanism that makes it so that when I stop rotating the green wheel and I hold it in place, the red one keeps turning.

PS: I'm building a flywheel (represented here by the red wheel) and the green wheel here is connected with a belt to a crank. I want to make it so that the flywheel keeps turning even when the crank is fully stopped.

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    $\begingroup$ The answers are correct; just thought I'd point out that you can find mechanisms like this in the rear hub of a bicycle and in the connection between a starter motor and the engine of an automobile. $\endgroup$
    – Carl Witthoft
    Commented Mar 3, 2016 at 15:37
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    $\begingroup$ To add another fun fact along with Carl's, it's this freewheel clutch that gives a bike it's characteristic clicking while the rider coasts. $\endgroup$
    – William S. Godfrey- S.E.
    Commented Mar 4, 2016 at 1:07

3 Answers 3

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It's called a "freewheel" or "overrunning clutch".

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Freewheel Clutch or
One-Way-Bearing or
Sprag Clutch:

enter image description here


More information:
Freewheel Clutch Types
Sprag Clutch Information
Cross+Morse Freewheel Clutch Catalog

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Another solution which is based on spur gears+springs rather than a clutch

Another solution which is based on spur gears+differentials rather than a clutch

Found using the keyword "rotation rectifier" (since it's the mechanical equivalent of an electrical rectifier in which alternating current is converted to direct current).

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  • $\begingroup$ Both of those mechanisms use ratchets to prevent reverse motion of a shaft. None of this is relevant to the original question. $\endgroup$
    – Dave Tweed
    Commented Mar 8, 2016 at 16:11
  • $\begingroup$ I was looking for that term in english, thanks. I beg to differ, as the OP has asked for a way to let the driven part rotate freely when the drive is removed, which is clearly demonstrated at least in the second solution at youtu.be/-p8zrvU-cYE?t=2m3s. Though I admit wear and load friction on the drive is not ideal, this is still a solution. $\endgroup$
    – Mister Mystère
    Commented Mar 8, 2016 at 16:58

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