well, i went on a short bike ride this morning (i do odd jobs around the neighborhood, this week i’m feeding a dog, cause the family went away). as i was riding, i was thinking about how the deraileur works, and this is how it works on a bike (or so i think)…
first, you have your cable, which connects the derailleur to the controls (only slightly important ;)). next you have the derailleur, and finally the controls.
so, let’s say you have a 7 speed bike (for simplicity), and you’re in gear one, and you want to go to gear 2. you hit/pull/push/twist/turn/etc. the controls (every bike has a different way of doing it, but i’m going to work with mine from now on). one my bike, hit one button, you go up a gear, hit the other, you drop one. this is the kind of control we would want, because then with a small piston, and a servo, or two pistons, or two servos, or however you want, you could make a shifter. what happens is when i hit the button to gear up, it pulls the cable, which pulls the derailleur, which moves the chain, and when i het the other button, it releases a bit of the cable, and the spring moves the derailleur back. now, if we were to rip the derailleur off of my bike, i know i could somehow hook it up in the robot to work, and work it would :D. so, i think as long as we have at least 2 servos, and two small pistons, i could make a derailleur work, if it had the right controls.
if however, you find a derailleur that works because you turn something, and that pulls or releases cable, that won’t work, because you’d need a motor, and why waste a whole motor to turn a small amount?
so michael, if you can find the right kind of derailleur, we could make it work. it wouldn’t look nice, but it would work.
also, all of the above could be completely wrong. heck, i’m a programmer, not an engineer! but, i do know some about the mechanical side, and this has got to be the most i’ve ever thought about the mechanical side :D.