[MrForbes]

I would recommend that you put two wheels next to each other on the rear of the robot on each side, in the fashion of a school bus (dualies), and then you'll have a 6 wheel robot with 4 wheel drive and easy to build Ackermann steering.

We plan on trying to set up the steering so the robot can turn very sharply, sort of like a forklift (but with front/rear reversed from a forklift), and making it turn that sharply pretty much rules out having shaft drive to the center of the front wheels like normal 4x4 trucks use. Instead, you want to make it work like a "crab drive" or "swerve" robot, and then it would not really make sense to bother with the Ackermann geometry.

also with a 2wd Ackermann system with very tight steering angles, it might be very helpful to have a programmed "differential" that drives the motors opposite directions to make the robot spin about the rear wheel center axis. We haven't figured this out yet, though.