Starting from the ‘‘inside out’’, t

Starting from the ‘‘inside out’’, the control architec- ture contains two inner motion-control loops. The inner-most loop is the wheel-level control, which acts to drive each smart wheel to its desired steering and drive speed set-points. The wheel-level controller uses simple PID control algorithms. Around the inner loop is the path-tracking controller. This loop derives the set points needed by the wheel-level control in order to force the vehicle to follow a desired path in space, where a path is defined as an arc in inertial space (with a prescribed velocity along the arc) and an associated vehicle yaw motion. The path-tracking controller uses a newly developed spatial tracking control algorithm that is described in more detail in Davidson and Bahl (2001).