Robots must be constructed of ONLY Lego bricks. The computer must be either an RCX or an NXT. Each robot is limited to one computing device, three motors, and four sensors of any type. Each person may build up to two robots.

Robots must be programmed for autonomous operation, and no human interference is allowed after a match is started.

Robots must be less than a 18" long, although height is unlimited.

Robots may not purposefully injure the sumo ring. Robots may not spray anything onto the ring. Robots may not interfere with other robots programs. You are allowed to try to damage the other robot.

In previous years, the Ring was several feet in diameter with a black outside perimeter line and white inside.
For 2009, the ring is made on a wooden platform and is 4 feet in diameter.  The main arena is black, and the outer rim is white.  Two grey lines near the center define the starting position.  (The intention is that the grey lines will not trigger the light sensors, but this will depend somewhat on your programming.)   An example of this type of ring is shown here.
In the future, either type of arena may be used, depending on external circumstances. Be sure to verify the ring coloring before finalizing your robot's program.

Each competition uses double-elimination rules.  (You need to loose two matches before you are eliminated).

Each match is between two robots.  A match lasts for either three bouts or three minutes, whichever comes first.

To start a bout, two robots are placed back to back in the center of the ring. (On the 2009 arena, the bots are lined up on the starting lines, facing away from each other.)  Each robot must have a five second delay on it after the run button is hit. No motors are allowed to move during this five seconds.  No remote starts are allowed.  The robots must move forward 8 inches before turning.

A bout ends when one robot is no longer able to move under its own power for at least 5 seconds, a robot is declared out of bounds, the robots are deadlocked for more than thirty seconds, both builders agree on a draw, or when the match time runs out.  A robot is declared unable to move under its own power when it cannot cause its position within the arena to change by more than 5 mm through its own efforts.  If one robot intentionally pins another robot so as to cause it to be motionless for 5 seconds, and if the pinning robot is also motionless during that time, both robots will time-out and the match will be a draw.  In order to prevent this, the pinning robot must conform to the above rule and must manage to move its own center of mass by 5mm while keeping its oponent motionless.  Note that on the old paper arenas (black line on white mat), a robot is declared out of bounds if it touches the floor outside the arena for more than five seconds.  On the new wood arena, a robot is declared out of bounds if it touches the floor, even just briefly.  This is an important difference to note, and is due to the fact that the wood arena is 2" off the floor, allowing robots to execute wide turns with parts of themselves over the line without being out-of-bounds.  This is a much less subjective definition than what is required for a paper arena.

Each bout is scored by two points for a win, one for a draw, and zero for a loss.

The match is over when three bouts have ended or the three minutes are up. If the robots have the same number of points, a sudden death round is played.

The robot with the most points at the end of a match wins the match.  If the losing bot has lost one other round, it is then out of the competition.

A maximum of one minute of repairs can be made between bouts. You are not allowed to reprogram during the competition. Longer repairs can be made after the end of a match.