[probizzle]

One quick comment that I would have is to also make a back-up drive system, which drives whatso-ever direction from the point of view of the robot. Your drivers I hope played enough video games to get this figured out (easily).

Just in case....
(and because your drivers actually might like this better, and because your absolute positioning system is going to drift, and it will be a hassle for drivers to figure out when to reset. etc.)