my team tested a tread system for the 2003 season. it had 4 trucks with treads. the trucks pivoted on the drive axle to allow more surface contact when climbing the ramp.
there is a picture here:
http://www.roboraiders.com/img/index...picture&id=258
and here:
http://www.roboraiders.com/img/index...picture&id=275
the treads were removed after testing because they produced to much drag when turning. the tread material was wrapped around the drive wheels and cut making it 8 wheel drive.