The ability to mathematically model the movement of a robot manipulator is a prerequisite to the understanding of the key factors that influence a manipulator's performance. This paper presents a manipulator model which has been used to simulate and control a real robot arm. A method of describing the arm by its rotational characteristics, a set of equations called the Inverse Arm, and an algorithm called Forward Arm are presented. The Forward Arm simulates the movement of an arm, and the Inverse Arm provides a means of computing thc correct voltages to apply to an arm to achieve a desired movement.