It‘s a shameless rip off of a vinyl record on a deck; but what you should get is all the various plates moving together at a set speed, unless friction is applied to the touch plate - then the slip mat should slip against the drive plate and the slip plate to allow the motor to keep rotating, despite the slowed speed of the touch plate. In addition, by using a large gear plate (could equally use a drive belt mechanism), and a small cog on the rotary encoder, you don’t need a hugely accurate encoder.

My thought is to make a smallish one of these, maybe 6" diameter, for use as a movie speed controller in Quartz Composer, via midi. The speed read from the encoder directly influences the speed of the movie; it should also allow for winding it back and forth and so on.

Conceptually it is about providing the physical feedback that is so often lacking in digital interfaces.

SteamSHIFT out.