[Rick TYler]

I agree with the last post. Have you ever noticed how much harder it is to steer a car going backwards? It's a lot less directionally stable than when it's driving towards the maneuverable wheels. The farther back you can move your drive wheels, the better off you'll be. Could you move your drive wheels to the center and put casters or even just skids on the front? It looked strange, but I saw a very drivable FRC chassis with traction wheels in the center, and fixed (non-swiveling) hard plastic casters (like from Home Depot) on each end. The casters rolled great in a straight line, but the hard plastic let them easily skid sideways. Simple, light and cheap -- perfect engineering.

A lot of very good chassis have drive wheels in the middle and two omnis at each end. We have two very successful FTC robots -- one has four driving wheels almost touching in the back (picture the dual wheels on a big rig tractor) and unpowered omnis at the front, and the other has driven traction wheels in the middle, driven omnis at back, and a pair of unpowered omnis on the front. The first bot ("Plan B") has the advantage of never being trapped next to a wall -- it can always pivot away. We actually have three successful FTC robots, but the third one is only 2-wheel-drive with unpowered omnis on the front.

Frankly, I don't think I've ever seen a chassis laid out with traction wheels at front and omnis on the back.

EDITED: The FRC bot with the fixed plastic casters had a problem with turning too fast. With the casters, the slew rate slowed enough for the bot to track straight and still turn like a -- well, like a thing that turns really fast.