[fox46]

If one were hellbent on an infinitely variable transmission, I would start with something like what is found in a snowblower: http://www.youtube.com/watch?v=hZD5toJyjyQ

Basically, the engine drives a round plate and small rubber wheel is driven by said plate. The shift linkage moves the wheel to different points on the round plate. As the circumference of the small wheel's contact patch changes you end up with different gear ratios.

It would be quite simple to build something like this- use a banebot wheel on a section of hex shaft and a mechanism to slide it back and forth depending on the desired gear ratio. You'd have to run it at fairly high speed though to minimize the slippage.