Robust Sliding Mode Control Design and Experimental Implementation for 4-DOF Underactuated Control Moment Gyroscope

This paper presents a robust sliding mode control-based strategy for an underactuated 4-DOF control moment gyroscope (CMG). The dynamic model of the system is derived using Lagrangian mechanics. While conventional linear sliding surfaces are effective for tracking control using reaction torque, they are not directly applicable when using intrinsic gyroscopic torque for the control of the unactuated state. To overcome this limitation, a novel sliding surface is proposed, specifically tailored to enable accurate tracking of the unactuated state via gyroscopic torque. The stability of the closed-loop system is rigorously established through the Lyapunov stability theory. The proposed control laws are validated experimentally on a CMG setup, and their performance is compared with that of a traditional proportional-integral-derivative (PID) controller. Experimental results demonstrate the superiority of the proposed controller in terms of tracking performance and energy efficiency, when controlling the unactuated state using gyroscopic torque. These outcomes highlight its effectiveness and practical applicability for robust control of underactuated CMG systems.