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How can I create a gear system which keeps, say, 60 rpm stable on output wheel, when I don't care about force? I am using a hand-turned crank as an input wheel.

I know a flywheel could be used, but it is weak to small accelerations and slowdowns over time.

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  • $\begingroup$ incorporate CVT like concept? $\endgroup$ Sep 18 '17 at 17:35
  • $\begingroup$ Something like that I think? I'm pretty new to professional mechanics, but the Wikipedia article seems good. $\endgroup$
    – hegez
    Sep 18 '17 at 17:54
  • $\begingroup$ What does your 'geared' system look like? Gears in general are hard-linked, so if you're cranking it then your crank speed is locked to the output wheel speed. $\endgroup$ Sep 18 '17 at 18:09
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Since this is fully analog, if you don't want to delve into extremely complex devices like a continuously variable transmission with ratio governed by deviation of output speed, your best bet would be to ballpark the input torque range and provide a strongly non-linear speed governor creating extra friction on output exceeding rated value.

Go with a centrifugal governor that upon exceeding preset speed activates a brake on the input shaft, with friction climbing rapidly as output speed is exceeded - say, the weights of the governor move jaws of a brake, engaging them as friction reaches the limit.

A somewhat simpler mechanism, frequently used in music boxes, uses viscous friction of air; a little fan driven by a set of gears increasing its speed relative to input, responds with torque of air resistance proportional to square of rotary speed. This is less accurate, but simpler and suffer less wear over time.

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  • $\begingroup$ A more desirable solution to braking the input might be a governor that disengages the clutch once RPM exceeds given threshold, torque of output on input shaft vanishing as speed increases, instead of growing. $\endgroup$
    – SF.
    Oct 12 '17 at 15:15
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The keyword you are looking for is a governor

The most simple type is a parted circle that are hinged to be able to move outward into a ring by centrifugal force and the friction counteracts the increased speed.

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  • $\begingroup$ And what happens if the speed goes below the design point? You've only solved half the problem $\endgroup$ Sep 18 '17 at 18:09
  • $\begingroup$ Yeah, 'specially if they stop turning the hand-crank. $\endgroup$
    – Transistor
    Sep 18 '17 at 19:22

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