A sliding mode control scheme for an underactuated unicycle

In this work we focus on the analysis and control of a unicycle that consists of a wheel and a saddle, in which only one actuator is used to generate a torque on the wheel, and the saddle is treated as an inverse pendulum. A sliding mode controller (SMC) with a hierarchical switching surfaces is designed such that the unicycle can reach any designated position while keeping the saddle stable. The instability of the unicycle system is explored through zero dynamics. With the proposed SMC, the stability of the sliding manifold is analyzed at the equilibrium and other operating points, and verified through simulations.