The authors have developed an electrical cart using two direct drive motors. It has two drive wheels and one caster wheel. A driver riding on the cart gives speed and steering commands through a joystick to operate the cart. Each motor is directly mounted into the drive wheel and is fixed on the body, frame. A speed difference between the two drive motors is controlled to turn the cart. Such a steering method which is called “differential-drive method” makes a great contribution to simplification of the mechanical structure.
First, modeling of the cart is discussed in this paper, because few researches have been done in which dynamic equations are derived theoretically. The validity of this modeling is verified by comparing experimental results with reasonably calculated ones. Second, the authors propose a control system with fuzzy theory to get stable straight runnig performance, which can keep the caster wheel stragiht as long as a driver wants the cart to run straight. This fuzzy control system produces such a control signal that the cart automatically runs straight even if anything which may disturb the straight running occurs. It is verified experimentally that the proposed fuzzy control system helps a driver to keep the cart in a straight course.