pic: Prototype Drivetrain

[gyaniv]

OK... This is really starting to annoy me...

Seriously, if you want a zero turn radius robot, you don't need to put 2 wheels in the mid and hope this will work...
you just need that all the wheels will get the same amount of torque and speed, and that all of them will be in the same distance from the center of the turning radius ( Even if it is zero turning radius there is still a center-point) . This will apply for 4WD.
For 6WD you need that the 4 outer wheels will be just like the 4WD logic i said above and that the 2 center wheels will be exactly in the center between the two other wheels at each side.

Another thing, when you design a drive-train take to consideration the specific game, for most teams this drive-train will be a disaster for LUNACY and BREAKAWAY since in those games the space in the center of the robot was important for the mission. you want that your drive-train will take the least space as it can on the robot, and weigh as low as possible so all the other resources can go to the other robot mechanisms. But don't forget that the drive system should be as much maneuverability as you need to the certain game, easy to control for the driver, and that will almost need none program correction as possible (unless you MUST).