It is a chassis that uses the inexpensive geared motor like the gm9 or gm3 from solarbotics. I used the treads and gears from http://www.thingiverse.com/thing:467807 . I just had to file a little the gear for the motor. It has holes for mounting an arduino uno and a L298 H-bridge module. There are also holes in front and the back to allow modules to be attached! The last photo shows the first two versions of the chassis. Support needed!!