The versatile Romi chassis is a great starting point for your next mobile robot. This kit includes all the basic mechanical parts to get up and running, including two motors, two wheels, one ball caster, and battery contacts. The wheels and ball are white; all other plastic components are red.
The Romi chassis is a differential-drive mobile robot platform with a diameter of 6.5″ (165 mm) and an integrated battery holder for six AA batteries (not included). The drive wheels are located on a diameter of the circular base plate, allowing for turns or spinning in place. A large, fixed ball caster in the rear provides a smooth third point of contact, and a second ball caster (not included) can optionally be added to the front. The chassis uses 70×8mm Pololu wheels and Mini Plastic Gearmotors with extended backshafts to enable quadrature encoders for position feedback.
The Romi chassis has an abundance of general-purpose mounting holes and slots intended for various sizes of screws (not included) such as #2-56, #4-40, M2, and M3. These holes can be used for mounting your electronics, such as your microcontroller, motor drivers, and sensors.
The plastic components making up the chassis are available in six colors, either individually (for use as replacement parts or to make custom color combinations) or in kits that include motors and battery contacts.
More technical information at Pololu.