A systematic approach to creating terrain-capable hybrid soft/hard myriapod robots

Multi-legged animals (myriapods) such as centipedes move effectively in diverse terrain; flexible bodies and limbs allow them to morphologically adapt to the environment. To examine how the variation in body/limb forms of myriapods affect the mechanics and performance of terrestrial locomotion, we built a low-cost multi-legged hybrid (containing soft and hard components) robot which has 8 segments, each with two limbs driven out of phase. The back elements and limb pairs are driven by servo motors. Building on new theoretical results from geometric mechanics applied to myriapods, we systematically tested gait patterns with different leg contacts and body undulation on various laboratory and natural environments including flat and uneven rigid ground, stairs, and unstructured natural terrain (leaf litter, grass). On flat ground, the robot with rigid components moved in the same way as the theoretically predicted gaits. As the complexity of the environment increased, the robot's performance suffered (and theoretical predictions became unavailable) due to deleterious interactions like jamming of limbs. However, adding flexibility into the robot's body parts (legs, body joints etc.) improved the open-loop locomotion performance (often to levels of that on flat ground) by either reducing the effects of environmental disturbances or increasing stability. Our findings show that in order to produce an agile, robust locomotive device, we need to understand the importance of body morphology and complex, dynamic interactions between an organism and its environment through systematic experiments in both the laboratory and natural environment.