The Pololu Zumo chassis kit contains the components necessary to build a small, high-performance tracked robot platform that is compact enough to qualify for Mini Sumo competitions. Each side of the chassis has an idler sprocket that spins freely and a drive sprocket that connects to a micro metal gearmotor (not included). The main body is composed of ABS plastic and has sockets for two micro metal gearmotors and a compartment for four AA batteries (not included). The battery compartment terminals protrude through the chassis and can be accessed from the top side. A black acrylic plate is included with the chassis. This plate holds the motors in place and can be used for mounting your electronics, such as your microcontroller, motor drivers, and sensors.