Quote:
Originally Posted by DonRotolo
Just beware: some worm gear drives are backdriveable. As with many things, it depends upon the exact design of the worm gearbox.
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To further expand on the science behind this, we start with the notion that all worm drives are backdriveable. This holds true if we have infinitely strong unobtainium worms and worm gears and/or infinitely awesome unobtainium grease that lowers coefficient of friction to zero.
What prevents some configurations of worm drive from backdriving is a high coefficient of friction between the worm and the worm gear, which means an exceptionally large backdrive force is needed. This exceptionally high backdrive force needed to overcome the friction means that the gear teeth will shear off before that level of force is reached.
A simple explanation for this principle uses the principle that a screw is just a inclined plane wrapped around a cylinder. Using only one angle component, we can see from the diagram below that the backdrive force F will cause the worm to backdrive if Fsinϴ > Fcosϴμ, where μ is the coefficient of friction between the two gears.
Since F cancels out, and sin/cos = tangent,
in simplistic terms you can state that a worm drive will backdrive if μ < tanϴ and F is less than the force required to shear worm teeth.
