High-Low Gain Redesign fo ra4D OF Spherical Inverted Pendulum

We revisit a previous high-low gain control idea for a 4 DOF spherical inverted pendulum using a different approach, inspired by a nested saturation tool proposed by Marconi and Isidori, that provides explicit tuning rules to deal with certain bounded external disturbances. The update controller is a robust, decentralized and "global" controller.