Back in my sophomore year in 2013, together with Jeroen Gillis, I made an Arduino-based sumo robot with which we competed in the ‘national’ finals at Ghent University. We finished 5th out of 44 teams, as the best KU Leuven team, and it was a lot of fun!
The robot’s pyramid-like frame comes from a metal computer case sidepanel, which I cut and welded together. Under the hood is a Lego structure holding together an Arduino, motor controllers and Lego motors with wheels. A key factor to our robot being among the best was its mirror coating, confusing enemy infrared-based distance sensors.
More info & photos see IEEE Student Branch Leuven.