Originally Posted by bairdco
here's a couple of things to consider;
steel sprockets would have to be used. because of the drag of the chain when switching from gear to gear, it would destroy an aluminum sprocket in a matter of days.
the average bicycle will not accomodate 3 sprockets on the rear. a 410 chain is almost 1/2" wide, and you need space between the sprockets for it to ride on. probably at least 2.5 - 3 inches on the left side.
the major force of the chain is on the top as it's pulled into the motor. while a derailler could work to shift the chain, it won't do anything to help the alignment. with three sprockets, the center one would have to be aligned with the motor, and the other two would be offset. this could potentially cause the chain to come off the side sprockets. also, if the center one was aligned, there wouldn't be enough room on the inside for another sprocket unless the motor was offset.
as cool as having gears would be, trying to adapt conventional bicycle gearing doesn't sound feasable to me. one good shift from 2nd to 3rd at 45 mph would probably rip the derailleur to shreds.
what i'd be interested in would be making a left side drive internally geared flip flop hub.
I would use #410 heavy duty bicycle chain, not the typical kit supplied 415 chain. A three sprocket stack is actually quite narrow...diagram below.
In addition to the fact that the sprockets need to be steel...the sprocket teeth on a standard cluster are slightly twisted. I'm sure this is done to ease the chain onto the next larger diameter sprocket when downshifting. Although not impossible to do here at the shop, I really don't want to make a special tool for an experiment. I'll try it with straight tooth sprockets.
I don't see any problems with alignment; but as you pointed out the deraileur may fly apart!
We'll see what happens.