Mini Sumo is a fun and exciting contest in which two robots compete to push the opponent out of the ring. The first robot to touch the ground outside of the ring loses the round. The winner of each match must win two-out-of-three rounds. The match winner moves up the bracket, single or double elimination brackets may be used depending on the number of competitors and time available. Each round has a 90 second time limit with a mandatory five-second start delay. Robots must weight under 500 gm, not exceed 10 cm x 10 cm size, and be fully autonomous - no radio control is allowed.
Mini Sumo is popular around the globe and kits are widely available. While the size and weight of a Mini Sumo robot is quite standard, the biggest difference may be the starting method. AHRC uses a manual pushbutton start, while other venues may require a remote control start.
Mini Sumo Kits
Great choice for both beginners and moderately skilled roboticists. The Zumo's textured tracks maintain high traction even when not perfectly clean. Adding weight until it reaches 499 grams is recommended.
A great kit for moderately skilled robot builders. It has more powerful motors than the Zumo and its wheels have slightly more traction as long as they are kept clean. The kit's electronics include motor drivers and line sensors but you'll need to add your own micro-controller and sensors for locating the opponent.
Design and build your own Mini Sumo robot from scratch. Here are a few examples from our members:
Tips for Making a Competitive Mini Sumo
Tires. The goal of a Mini Sumo is to push hard, so high traction tires are vital. Silicone rubber and Polyurethane tires with a durometer of Shore A 20-30 range work great. Natural rubber tires used in slot car racing also work well but require much more maintenance. Slick tires can provide the best initial performance but lose traction quickly as they pick up dust from the environment and require frequent cleaning. Textured tires may initially have slightly lower traction, but do not need to be cleaned after every round and can eventually beat slicks that aren't cleaned regularly.
Weight. A Mini Sumo robot should be as heavy as possible while staying under the 500gram limit. The heavier the robot, the more weight it will have pushing the tires down against the ring to develop higher traction. Making a 10x10cm robot weigh 499 grams can be surprisingly difficult. Some ways to get there include:
Copper and Brass have good density (8.7-8.9 g/cm3) and is not difficult cut even with simple hand tools if you're patient.
Steel has slightly lower density (7.8 g/cm3) than copper and is much harder to cut, although it is a bit cheaper.
Tungsten has very high density (19.2 g/cm3) but is extremely difficult to cut. It is best to find a pre-cut piece that is exactly the size you need. Tungsten putty can be a great way to add weight in oddly shaped areas.
Lead is dense, cheap, and easy to cut but is not recommended due to health and safety concerns.
Balance. A Mini Sumo robot's center of mass should be as low as possible and its wheels should not be too large to avoid tipping over. When adding weight, it is best to add as much as possible to the bottom of the robot. It's tempting to think the motors and battery will be the heaviest part of a Mini Sumo and therefore should be as low as possible. If you're trying to hit 499 gram weight, the heaviest part of your Mini Sumo will be the 150 to 250 grams of metal that you'll need to add. Put as much of that metal as possible on the bottom and everything else can stack on top of that. As far as wheels, something in the 2.5 to 4 cm diameter range is a good bet. Wheels over 5cm in diameter usually result in a robot that tips over too easily.
Sensors. Mini Sumo robots generally have a line sensor on each front corner to sense the edge of the ring as well as some kind of sensor to look for the opponent. The line sensors are almost universally some type of IR sensor, while sensors that look for an opponent can vary quite a bit. IR distance sensors such as Sharp Proximity sensors, Time of Flight sensors, or a Protractor sensor are all good options. Ultrasonic sensors can be used as well but can take up a bit more space and may have slower response time. Microwave radar sensors are another option that have been used successfully.
Power and Speed. Mini Sumo robots often find themselves chasing each other in a circle, so a faster robot will be able to get in behind the opponent and push them out. With a bit of planning, its not too difficult to put together a set of motors, driver, and battery combo capable of peeling out on the ring surface. It is important to have power and speed but it's easy enough to accomplish that it doesn't need to be at the very top of the list. Have a look at some of the Mini Sumo kits below to get some idea of what works.
Stealth and Trickery. Most Mini Sumo robots attempt some level of camouflage so the opponent's sensors won't see them. IR sensors will not be able to see a black robot very well, while a soft-skinned robot (foam, cloth, etc) can be difficult for ultrasonic sensors to see. Some robots employ tricks such as dangling a white flag off the side like a matador to attract the opponent to their side. Some Mini Sumo competitors may have a stick protruding off the front like a joust which is very handy for tipping over big wheeled or top heavy competitors. No single trick works equally well against all Mini Sumo competitors, so it is still important to get the fundamentals right when it comes to Tires, Weight, and Balance.