Controllability analysis of planar snake robots influenced by viscous ground friction

This paper investigates the controllability properties of planar snake robots influenced by viscous ground friction forces. The paper provides three contributions: 1) A partially feedback linearized model of a planar snake robot is developed. 2) A stabilizability analysis is presented proving that any asymptotically stabilizable control law for a planar snake robot to an equilibrium point must be time-varying. 3) A controllability analysis is presented proving that planar snake robots are not controllable when the viscous ground friction is uniform, but that a snake robot becomes strongly accessible when the viscous ground friction is non-uniform. The analysis also shows that the snake robot does not satisfy sufficient conditions for small-time local controllability (STLC).