116 went to a 6WD for a variety of reasons this year, namely the turning issues with our 4WD traction-wheeled bot in 2006, as well as the shorter length between wheels increasing our ability to climb ramps.
Our 6WD incorporates 6 6" AndyMark Performance Wheels, with rough-top nitrile tread (same as seen on 1345's bot). We have a Andymark 2-speed shifting transmission, with 2 small CIM motors on each side. This is further reduced by a 12:30 sprocket reduction to the 6" wheels, giving us theoretical speeds of roughly 4 fps (low) and 10 fps (high) including inefficiencies. We designed the drive-train in such a manner that center wheel could easily be lowered if needed, and we can lower it at any point we wish by removing 8 bolts and adding spacers between the frame and center bearings. Currently, we are running the wheels co-planar, and it handles outstandingly in low gear, but not as well in high. If we deem that we need to use our high gear (and turn in our high gear) more in Atlanta (we very rarely needed to use it in Richmond), we may lower the center wheel.
So far the drive-train is our best in recent history (just ask our driver), is durable, and easy to maintain. We have only thrown one chain so far (in our first match), and even throwing it didn't really hinder our ability to drive (due to separate runs between wheels). The system is lightweight (under 50 lb.s for our entire drive-train and frame assemblies), easy to construct, and quite effective. It has given us more than adequate pushing power in direct pushing matches, but (like virtually every robot FIRST) can still be rotated by an opposing bot. It has also been able to climb every ramp we've encountered (even some very narrow and precarious ones, although some credit for that must be given to our driver).
http://www.invisiblerobot.com/roboti...h/p1280253.jpg