The design posted here calls for a differential. A differential solves exactly the problem you describe. I suggest reading about it on howstuffworks.com or something, but essentially, it will allow one wheel in a truck to spin faster than the other, and therefore drive over a different radius. [edit] heres a relavent page
http://auto.howstuffworks.com/differential1.htm[/edit] In fact, this is what car companies use to let cars turn.
advanced traction systems use these, but if im not msitaken, they are even more complicated because they allow forcing more power to one output shaft or the other, not just letting them balance out. [more_edit] howstuffworks.com is great, keep reading in that article, they explain this, too. Check out the viscous coupling. I'd like to see some team implement that
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