Meeting Abstract
Animals often move through complex terrain by transitioning between locomotor modes. For example, to traverse grass-like beams, the discoid cockroach can push across, climb over, or roll its body to maneuver through gaps. Interestingly, the animal frequently transitions from more difficult (slower) locomotor modes (e.g. climbing, pushing) to the easiest (fastest) rolling mode. In addition, its body vibrated vigorously during traversal due to oscillatory leg pushing against the terrain. Inspired by these observations, we hypothesized that kinetic energy fluctuation from the seemingly wasteful body vibration helps legged animals explore a locomotion energy landscape and overcome potential barriers to find more favorable locomotor modes. We tested this hypothesis by studying how cockroaches and a robophysical model transitions from climbing to rolling when traversing grass-like beams and modeling their locomotor-terrain interaction using a locomotion energy landscape. We found that both systems overcame a lower potential barrier to traverse by rolling than by climbing, i.e., the rolling mode was terradynamically more favorable. In addition, as kinetic energy fluctuation decreased relative to mode-separating potential energy barriers, the animal was more likely and needed a longer time to transition from climbing to rolling. Kinetic energy fluctuation helps animals and robots overcome mode-separating potential energy barriers to explore the landscape to escape from less favorable modes and find more favorable modes. Our study demonstrates the usefulness of locomotion energy landscape for understanding how macroscopic, self-propelled, legged locomotors interact with terrain to probabilistically transition between locomotor modes, and is a step in establishing terradynamics of locomotion in complex 3-D terrain.
