The wheels are all in line -- there's no 'rock' at all. The chain is #25.
Because the center wheel is not lowered at all, at least one outside set of wheels should be omniwheels to alleviate friction while turning. I chose to put a set on each end because there's no penalty to in line pushing force, generally, and I like to subtley encourage our drivers to avoid conflict.
I'm now looking at a mounting scheme that will accept bumpers and protect the wheels from impact. I've never put bumpers on a robot before, so I'm looking at examples of others' work to get an idea how to best accomodate the additional weight of the bumper assembly.
Our 2005 robot had a lowered center wheel and the tipping action drove me and our drivers crazy. It's an impact to the system each time the robot's inertia shifts and that starts to lead to annoying things like loosened bolts and the like. Practically, it's cheaper and easier for me to make omniwheels than it is to make traction wheels and it's certainly cheaper than buying them.
As shown -- which includes everything but stiffening gussets and a base upon which to mount electronics, it's 29.5 lbs.
The omniwheels are riding on 5/8" keyed shaft, while the AndyMark performance wheel is broached for a 1/2" hex shaft. It'd be relatively easy to change out a set of omniwheels for a set of traction wheels with a little bit of forethought. Namely, I'd need to make some shafts that are 5/8" diameter with keyway on one end and 1/2" hex on the other.
I'm waiting on the game before adding cross-bracing since I'm not sure if I'll need a scoop or something on one or both ends. I'd like to, if weight allows, put an aluminum plate (1/16" or so) across the bottom to add rigidity.