This post kind of describes our system.
http://www.chiefdelphi.com/forums/sh...43&postcount=5
There is a 9 tooth sprocket on the transmission, and 22 tooth on the roller. We are using hollow 1/4" round urethane belting from McMaster-Carr.
We haven't experimented with different sizes, we just used what it appears that other successful teams have been using for several years.