From the Wikipedia page on Robot Sumo:
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__Robot-sumo__, or pepe-sumo, is a  [sport|https://en.wikipedia.org/wiki/Sport]  in which two  [robots|https://en.wikipedia.org/wiki/Robot]  attempt to push each other out of a circle (in a similar fashion to the sport of  [sumo|https://en.wikipedia.org/wiki/Sumo] ). The robots used in this competition are called sumobots.%%sup [[1]/%

 [|https://en.wikipedia.org/wiki/File:RoboCore_Robot_Sumo.jpg]   Robot-sumo

The  [engineering|https://en.wikipedia.org/wiki/Engineering]  challenges are for the robot to find its opponent (usually accomplished with  [infrared|https://en.wikipedia.org/wiki/Infrared]  or  [ultra-sonic|https://en.wikipedia.org/wiki/Ultra-sonic]   [sensors|https://en.wikipedia.org/wiki/Sensor] ) and to push it out of the flat  [arena|https://en.wikipedia.org/wiki/Arena] . A robot should also avoid leaving the arena, usually by means of a sensor that detects the edge.

The most common "weapon" used in a sumobot competition is an angled blade at the front of the robot, usually tilted at about a 45-degree angle towards the back of the robot. This blade has an 
adjustable height for different tactics.

Robot-sumo is divided into classes, fought on progressively smaller arenas:

* Heavy-weight. Standard in the  [National Robotics Challenge|https://en.wikipedia.org/wiki/National_Robotics_Challenge] . Robots may weigh up to 125 pounds (56.8 kg) and fit in a 2-foot cube (61 cm).
* Light-weight. Also standard in the [National Robotics Challenge|https://en.wikipedia.org/wiki/National_Robotics_Challenge] . Robots may weigh up to 50 pounds (22.7 kg) and fit in a 2-foot cube (61 cm).
* Standard class (sometimes named Mega-sumo) robots may mass up to 3 kg and fit inside a 20 cm by 20 cm box, any height.
* Mini-sumo. Up to 500 g mass, 10 cm by 10 cm, any height.
* Micro-sumo. Up to 100 g mass, must fit in a 5 cm cube.
* Nano-sumo. Must fit in a 2.5 cm cube.
* Pico-sumo. Must fit in 1.25 cm cube.
* Femto-sumo. Must fit inside a 1 cm cube.
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