Rug Warrior I (1993) by Joseph Jones (iRobot) and Anita Flynn (MIT AI Laboratory), MA. The Rug Warrior class of robots are microprocessor controlled and have ten sensors and two motor drivers onboard. Rug Warrior I here has a cylindrical bump skirt for detecting collisions and is driven by two motors in a differential manner. A nylon caster mounted on a non-rotatable axle slips on the ground when the robot turns. “An important problem for a differential drive robot is how to ensure balance. Some additional support, besides the two drive wheels, must be provided to prevent the robot from tipping over. Usually this is done by adding one or two caster wheels, arranged in a triangle or diamond pattern.” – Mobile Robots: Inspiration to Implementation, by Joseph Jones and Anita Flynn.