We detail the design and construction stages of a computer-controlled, four-degree-of-freedom, planar manipulator. The arm is redundant in the horizontal plane to allow studies in self-motion control and redundancy management. The joints are revolute, prismatic, revolute, revolute (RPRR) resulting in a more-than-minimum configuration. Each joint is actuated by a direct-current (DC) motor equipped with an incremental encoder for angular position sensing. A model of the system is developed that includes the coupling nonlinearities as well as motor dynamics and each servo plant is then transformed to its discrete-domain equivalent for modelling and parameter identification purposes. Computer simulations illustrate the performance of the manipulator and experimental results are included which support the theoretical analysis.