[sanddrag]

You mentioned building a two speed. I actually don't think it would be that difficult at all. Maybe a little expensive. If you got the pneumatic kit for it, I bet it would be fairly easy to hook up a cylinder to a shaft and have it slide the shaft with the gears on it to make a mesh style shifter. You'd just have to make sure you got two different ratios that have the same number of total teeth between the two meshing gears (same c-c distance). Also, with the relatively slow speeds and loads involved, I bet even those plastic gears could stand up to it.

*Afterthough* Aww heck, now that I think about it, since it is on such a small scale you could probably just use an inexpensive servo and linkage to slide the shaft. QUICK, go buy more gears and frame metal!