Contact-implicit Modeling of Snake Robot Sidewinding on Compliant and Granular Terrain

Snake robots generate locomotion through many simultaneous ground contacts, making them a challenging platform for model-based control. Contact-implicit trajectory optimization has shown success for legged and manipulation systems using rigid contact models, but its application to snake robots has been limited due to the complexity of distributed, contact-rich interactions. In this work, we propose a modeling approach that extends rigid contact formulations to snake robot locomotion and demonstrate that such models can also be adapted to deformable terrain. We evaluate this framework using two complementary simulation tools—Simscape Multibody for rigid ground and Chrono’s Soil Contact Model for compliant terrain, and validate the predictions through experiments on rigid ground and sand. Results from both simulations and hardware experiments show that across multiple gaits and gait frequencies, both the rigid and compliant ground models capture the dominant locomotion signatures, direction of travel, and head motion trajectories observed in experiments.