Gravity-Powered LEGO Bricks Deliver Perfect Moves in Tic-Tac-Toe

Joost van Velzen spent years creating a Tic-Tac-Toe machine made from thousands of LEGO bricks, and the end result is a stunning 18th Century-style cabinet with a medieval knights motif. Shields mark human movements, while small crossed swords mark mechanical reactions. The monster was made from 4998 parts and has over 200 moving elements. There are no electronics in sight, just plain old-fashioned mechanics.

The game begins by twisting a dial, which initiates gameplay. The machine then places a pair of crossed swords in the center square. You press one of the eight keys around the board to install a shield, and the machine automatically inserts its own sword. Turn the dial again, and the board advances to the next stage, and so on until someone wins or the board is full.

Gravity contributes to the movement, pushing the signals up the cabinet. Then they are dragged back down to their starting position because that is how it is designed. There is a decision engine, which is essentially a chain of 52 logic gates. These are mostly made of L-shaped Lego pieces that serve as OR gates; when you push one, it raises the output. AND gates, on the other hand, rely on two sub-assemblies that only align when both inputs are in the correct positions.

There are two OR gates that can handle eight inputs each, which is useful when you need to make a few decisions quickly. The memory sits at the bottom, on a brown plate that moves ahead with every full turn. It’s a brilliant system in that the arms move in and out depending on which key you hit, preventing or allowing particular bits of memory through. It allows the entire thing to store 204 bits, which contain every single game state and the appropriate counter-move for each.

It’s all based on a spreadsheet, which helped Joost devise an unbeatable approach and draw it out across six steps. Each step must account for two alternative human movements and sequence the sword replies. A red element appears first to certify the move’s validity, followed by blue components sending a signal to the AND gates, which control the swords and shields. Both appear at the same moment, which is really cool. When the game is over, a couple of hidden knobs reset the display, and a lever and a half-turn of the dial clear the memory for the following round.

Joost was testing the logic in a prototype with bright colours, which allowed him to alter anything on the go. Once he was satisfied, he planned the look of the thing, bought the parts, and built the final version, which of course required further testing at each level. However, a few natural pauses and small successes along the way saved the whole thing from becoming overwhelming. His finished cabinet is now on the LEGO Ideas website, attempting to garner enough support to be released as an official set.
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