Snake robot uses vertical bending with force feedback control to traverse large obstacles

Snake robots are promising in traversing 3-D terrains as well as snakes do. Despite many previous studies using lateral bending for propulsion, snake robots still struggled on 3-D terrains using these gaits even with compliance to adapt to height changes. Vertical bending can push against terrain height variation for propulsion (Date and Takita, 2007 IROS; Jurestovsky et al., 2021 JEB; Fu et al., 2021 SICB), which can potentially dramatically expand the source of propulsion to improve performance in 3-D environments. To understand how to effectively utilize vertical bending, we use a snake robot to test two hypotheses: (1) With large height variation, vertical bending alone can generate substantial propulsion; (2) With force feedback, propulsion can be better maintained. To test the first hypothesis, we controlled the robot to traverse a large obstacle under different backward loads. The robot generated propulsion 3 times its own frictional drag by propagating a fixed vertical bending that matched obstacle shape down the body. To test the second hypothesis, we challenged the robot with unknown obstacles and checked whether force feedback control improved performance. The robot indeed maintained better contact with terrain without reducing active pushing when using force feedback.