All I can say, whatever you do, make sure you build a prototype. I saw a team cut apart half of their robot to pull their transmissions at a regional this year because it wouldn't drive. I'd hate to see it happen again.
I don't know if you saw it or not this year, but we built a very simple 4 speed, 4 motor transmission. All you really need is a lathe and a drill press with an x/y table (or just a mill). The 2 motor aspect is done by linking the drill in low and chip motors with chain and sprockets (3-1 reduction I think). It's incredibly easy to build, we had a sophomore do most of it in two meetings. It's cheap, too, and you can make a 2 speed by simply cutting it in half...or you could save yourself the trouble and only build half of it!
Out lead engineer, Jim Zondag just finished drawing it in inventor and "I'm still working on exploded assembly veiws, parts lists, detail drawings, etc." It should be in the whitepaper section very soon.
He did, however, send me a picture of the drawing. It's pretty
