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Originally Posted by Sean Schuff
3. The gears in the gear train all ride on bearings and a simple shaft with thrust bearings separating each pair. The reduction is a stair-step effect from one end to the other.
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Ooh, that's a neat idea. It's surprisingly simple, and it lends itself well to basically
any number of reduction stages. It does have a whole bunch of gears running all at once, though, so it might be a bit more lossy than other designs.
I think with that many positions, an electric motor with position feedback is an appropriate way to shift it. Something like a rack and pinion, or a cam, or even a chain or belt drive. Or perhaps someone can think up a direction-switching ratchet mechanism with mechanical stops at each position, and use a pneumatic cylinder to drive it. I can also imagine a cam shaft controlled by a servo that controls which gear the shifter will stop at.
I'm a software guy without a lot of real mechanical experience, so I don't know how worried to be about the edges of the "power take-off" gear as it moves from one position to the next. It would seem to be susceptible to severe grinding if you don't have the speeds well matched.
What would happen if you moved the shifting mechanism to a spot between the two stacks of reduction gears, so that it could alternately contact either the "orange" or "blue" gears on both sides? You might get away with half as many reduction stages that way. [EDIT]Whoops, they're going opposite directions, so you'd need an extra idler gear to account for it, and the clearance is probably not reasonable anyway.[/EDIT]
I can't remember who posted the three-speed shifter with the internal doglike ball bearing "gear capture" mechanism, but I can imagine putting something it inside the "blue" stack in place of the external "pink/yellow" part. Does that make sense?