FFCS2AVHHS9ROIT.LARGE

Instructable user OddBot built this Arduino-controlled Tic-Tac-Toe robot built out of K’Nex (actually, he used LOZ, a K’Nex ripoff product) using ping pong balls. He controls the robot with a universal TV remote and an IR receiver, and you can actually configure the game with the remote, setting up (for instance) a larger board like 5×5.