Bart is taunted by school bullies Nelson, Jimbo, Dolph and Kearney because he does not have a 10-speed bike as they do. In order to get Homer to buy him one, Bart has his current bike run over by Dr. Hibbert's Mercedes-Benz G500. Homer buys the 10-speed for Bart, but refuses to pay the small assembly fee and builds it himself. Bart is happy since it looks great and works perfectly at first, but it falls apart when he moons the bullies. Homer, wanting Bart to be proud of him, tries to build a battle robot for the show "Robot Rumble". He fails to construct one, but then decides to build a robot with himself in it, which Bart names "Chief Knock-a Homer". Unaware of Homer's ruse, Bart enters the robot in the Rumble.