This was the second sumo-bot I submitted into the NXTLog sumo challenge. It had a comment by Steven Hassenplug saying that is was well documented but it never made it to the 30 selected.
I went through many modifications to get it perfect and now i think i got it. i have two wheels from the mindstorms set and small wheels for the back. the spikes on the side are just for show. i put rubber stopper on at an angle to allow the dragster to go backward on its own, but won't go backwards when pushed.
the program is fairly simple is waits 3 seconds, moves forward and then turn around. then if it "sees" an opponent it will CHARGE!!! if is senses the white line it will "wiggle" forward!
This bot was able to push 4 pounds.
How exactly did you find this 3 years later? XD No, I kid.
The way it works is its on slanted beam, which is attached to the robot by a smooth pin. It allows the robot to move forward, and it just slides along. But as soon as the robot moves backward (being pushed by another robot) the rubbers hit the ground, and the beam tilts backward, causing even more friction. In theory this would stop the robot from moving.