Lyapunov-Based Kinematic Anti-Prance Control for a Modular Rimless-Wheel Exploration Rover

The Scout rover is a novel rover concept developed by the German Aerospace Center (DLR) for the exploration of extreme extraterrestrial environments. Its locomotion platform is designed to tackle rough and rugged terrain, rock and boulder traverses, craters and cave systems on foreign celestial bodies. The Scout features a modular design with a compliant rover backbone and elastic rimless wheels. The backbone consists of rigid segments which are coupled by elastic vertebrae in-between. Under unfavorable conditions, the backbone deflects vertically, individual segments rear up and the rover begins to prance. Unintended backbone deformation and rearing-up negatively affect rover locomotion capabilities. This contribution presents a robust kinematic chassis controller for monitoring and controlling the backbone configuration. The backbone deformation is generically modeled upon an elementary backbone unit based on the nonlinear beam theory and a kinematic surrogate model. Lyapunov theory is used to synthesize a backbone controller upon the surrogate model for the elementary backbone unit. A kinematic chassis controller is established upon the elementary backbone controller in order to reduce unintended backbone deformations on chassis level. The overall controller is verified by means of test scenarios on different terrains on the Scout outdoor testbed. The controller significantly reduces backbone deformation on rough terrains.