Hybrid Controller for an Unmanned Ground Vehicle with Non-linear/Hybrid Dynamics

This report presents a method of controlling an unmanned ground vehicel (UGV) by employing hybrid control theory. The linear dynamics of the UGV near a straight path conform to modern linear quadratic regulator theory. Two different methods for regulation of the UGV on a straight track are analyzed. The first method employs the steering angle as an input, while the second employs the derivative of the steering angle as the input. While steering angle feedback offers a solution of lower state dimension, it was found that the noise in the steering angle command was too large for driving typical servo motors. When the UGV is turning the linear dynamics are violated. At the accelerations required for our UGV during cornering, side slip cannot be neglected. As the vehicle skids while cornering, linear assumptions are violated. Various surfaces can also change the cornering accelerations at which significant tire slip occurs. A simple yaw rate feedback PID controller is employed in an attempt to maintain a constant acceleration during the turn and ensure system robustness to environemental variations. Due to the continuous motion of the vehicle, the discrete modes of the controller, and the discrete properties of the UGV’s transmission, the system must be controlled considering hybrid automaton theory. A switching scheme is therefore developed to effectively switch between the straight mode’s linear quadratic regulator control and the turning modes yaw rate feedback PID control.