[s_forbes]

As the conversation has drifted more towards true skid-steering drivetrains, I thought I'd point out my favorite: 1662 in 2006. Their drivetrain was very similar to the one posted at the beginning of this thread, but instead of six kit wheels, they had a four-wheeled drivetrain with 2"x8" IFI wheels. Talk about a robot that's hard to turn!

For those of us that aren't able to pull of such feats, six wheel drive with a dropped center works great. I would just recomend (as several others already have) that you add some bracing between the side rails of the chassis. I would prefer stickier wheels, too, but as it sits it looks like a solid base for your bot.