From pololu.com: “The Pololu Zumo robot is an Arduino-controllable tracked robot platform that is less than 10 cm × 10 cm—small enough to qualify for Mini Sumo. It includes two micro metal gearmotors coupled to a pair of silicone tracks, a stainless steel bulldozer-style blade, an array of six infrared reflectance sensors for line following or edge detection, a buzzer for simple sounds and music, a 3-axis accelerometer, magnetometer, and gyro for detecting impacts and tracking orientation.”