A two wheeled robot with a pair of motorized wheels mounted on each end of a body and a rearwardly extending tail. The body comprising a chassis with sides and exterior side surfaces and providing an accessory mounting interface. The interface having a matrixical arrangement of threaded holes and one or more landings, the landings having an outwardly facing planar landing surface with hole openings at the landing surface. An accessory with a robot mounting interface cooperates with the chassis at the accessory mounting interface such that prior to fastening the accessory has a single degree of freedom of movement. Screws extend through portions of the accessory into select ones of the threaded holes of the matrixical arrangement.