[sanddrag]

Perfecting a robot to turn well is one of the greatest challenges in FRC robot building. We have been in it for 5 years now and still haven't quite perfected it. I'd say the best handling robot we've had so far was wider than it was long and had four wheels. It had Skyway 8x2 beadlok wheels (very short wheelbase and wide track) with the foam rubber tires which were turned down to smooth/flat on a lathe. It was very easy to keep straight but turned with authority any time you wanted it too. The wheels were pretty high traction on the carpet and it still drew a good amount of current while turning, but it was a very well handling machine. It is also important to mention that this robot had a very low CG and was only 13" tall total.

I think the one of the best configurations for turning and handling is to have a robot whose track width is significantly more than the wheelbase. However, if the robot's CG gets too high, or you have to climb a stair of something, it might not be possible to have it wider than it is long, especially with the 28" base dimension that was new this year.

So, getting a long skinny robot to turn is the real challenge. And this is where the craze over six wheels came from. We jumped on the bandwagon and it is good, but it still isn't perfect. I like the wide and short four wheel setup better. We had the weight over the back four most of the time so it tracked pretty straight but turning still wasn't superb with our super grippy McMaster tread. On the other hand, team 968 had a long 6 wheeled robot but they had it well balanced over the center wheels. It could spin in any direction at any time with minimal effort and great ease, but if you wanted to keep it in a straight line, it's not easy, it takes some skill.

One thing I saw done on a long robot was six wheels all touching the ground but the back ones were very close together and the fronts were non driven omnis. This way, it is as if your wheelbase was very short for the purposes of turning, but long for the purpose of stability. I didn't watch it too closely in competition but from what I saw it looked like a fairly effective setup.

I'm thinking 4wd tank on a wide bot can perform to meet a standard which I call perfect, but I still don't know what the "right" answer is for turning long FRC bot. 6wd with the center ones lower comes close, but it's still not perfect.