This paper studies the effectiveness of various controller design approaches on a flexible robot arm. The robot arm model used is that of Cannon-Schmitz flexible one-link robot. It is shown that the conventional PI controller cannot stabilize the closed-loop system. The idea of controller design using the stable factorization approach is explored. The controller design procedures, both with and without constraints on the actuator torque are discussed. The simulation results shows better system performance can be achieved by using these controllers instead of conventional LQG controller. The conclusion of this paper is that the stable factorizatlon approach has great potential in the area of flexible robot arm control.