A Noughts and Crosses Robot: From 3 × 3 to 4 × 4

Introduction

Noughts and crosses (tic-tac-toe) is a classic game in which two players take turns placing their pieces on a 3 × 3 board. The first player to form a horizontal, vertical or diagonal line of three matching pieces wins. On the standard nine-square board, neither player can guarantee a win against an opponent who plays perfectly. To explore a larger playing space, I extended the game to a 4 × 4 board in a later version.

In early 2007, during my first year as an undergraduate, I designed my first noughts and crosses robot. Two motors moved the mechanism along the X and Y axes of the 3 × 3 board, while a third motor released a piece onto the board. I used a worm gear and a moving shaft to convert the LEGO motor's rotary motion into the linear motion needed to push the pieces into place. An inexpensive light sensor detected the colour of each piece.

The robot won first prize in the University of London's 2009 Cool Computing Competition. Watch the original robot in action.

A Lightweight Noughts and Crosses Robot

I redesigned the robot in the summer of 2010, using a stationary game board and replacing the worm gear system with a continuous conveyor belt. Two colour sensors replaced the original light sensor to detect pieces more quickly. The entire robot fits on a standard 30 cm × 30 cm LEGO baseplate.

Watch the redesigned robot in action in the video below.