The decision to use (4) independent drive and steering motors ((8) drive motors total) was based on the desire to operate in several different pivot modes and to be able to also incorporate an overt chassis "twist" ability into Crab mode.
See
http://wiki.team1640.com/images/4/46...th_a_Twist.pdf as a reference.
Wheel diameter is 4". Chain is type 35.
Regards,
Clem