[Image by RoboCore Robot Sumo by Paulolenz via Wikimedia Commons, CCA-SA 3.0]

In human competition, one could argue that there is no purer expression of sport than pitting one person directly against another in some form of wrestling. Though robots aren’t yet advanced enough to wrestle with one another in the Greco-Roman style, a simplified form of sumo wrestling has become a very popular robo-sport. The concept — push the other robot out of the ring — is simple, but mastering it against other competitive robot builders is a huge challenge.

Rules

Rules of this sport can vary, and as outlined here, two popular specifications are the Japanese class, which can be up to 20 cm x 20 cm in area and up to 3 Kg in mass, and the mini class, which must stay within a 10 cm x 10 cm and weigh in at under 500 g. Interestingly, neither of these classes have a height restriction. This can be used creatively, perhaps to implement a scoop that drops down once the competition starts.

These autonomous rovers must be non-destructive, so attaching a hammer to one might work for other competitions, but is frowned upon in the disk-shaped sumo arena. Also, robots in the competition are not supposed to leak fluids, emit smoke, or entangle other competitors.

Robot builds

If you’d like to participate in one of these competitions, you’ll need a physical chassis. There are many kits available, such as this Arduino-compatible tracked robot platform from Pololu. Interestingly, this robot features an Arduino shield on the top of it, which an Uno board plugs into upside down. This makes the robot extremely modular, so a different development board in this form factor could be substituted, such as the more powerful Arduino 101, or even the ST Microelectronics STM32 Nucleo.

[youtube=https://www.youtube.com/watch?v=8pEOUdUndys]

Other options include this BASIC Stamp-based SumoBot Robot Competition Kit from Parallax, or if you’d like to control everything that goes into your robot, you can build it from scratch. For example, this Arduino Sumorobot, seen on Instructables is a great place to start. It features a chassis made of PCB material, as well as infrared line sensors and two photoelectric distance sensors.

The three robots listed here all feature a similar design, with either two wheels (or two tracks) controlling movement, and a scoop on the front meant to push your competition out of the ring. Where things get interesting build-wise is what sensors are used, and how they are programmed. The Zumo robot features six infrared sensors, an accelerometer (which can be used to detect when collision is made with another robot), magnetometer, and a gyroscope. Sensors can help you find and push your opponent, but making sure the robot doesn’t simply drive out of the ring on its own is also critical. And yes, this does happen, certainly to the horror of the robot’s creator or creators.

Strategy

Although there are many ways to program sumo robots, it’s summed up nicely here as, “Find the opponent, and push.” In the video below you can see a slightly more involved strategy, implemented in a competition where all participants started with the same kits. The program instructs the robot to move forward, then turns until it sees its competitor and pushes.

[youtube=https://www.youtube.com/watch?v=yPVsaZa7OyY]

Assuming a robot doesn’t drive out of the ring on its own, traction with the ground often becmes the deciding factor. A low center of gravity can help keep wheels stuck to the ground, and competitors generally try to come as close to the maximum weight limit as possible. Though it’s certainly difficult to watch helplessly as your robot triumphs or makes critical mistakes in the ring, pitting your ‘bot against others can help you refine your strategy and robot for the next competition!

Jeremy S. Cook is a freelance tech journalist and engineering consultant with over 10 years of factory automation experience. An avid maker and experimenter, you can see some of his exploits on the Jeremy Cook’s Projects YouTube Channel.