Importance of body and leg adjustment for traversing cluttered terrain

Although robots are good at avoiding obstacles, in critical applications like search and rescue in cluttered terrain like earthquake rubble, they must traverse obstacles using effective physical interaction, an ability still missing from most robots. Here, we study how the ability to adjust body parts and legs contributes to cluttered terrain traversal using animal and robophysical experiments. To traverse grass-like beams, cockroaches adjusted their head, body, abdomen, and legs in coordination. As the animal pushed against the beams, its body pitched up due to terrain interaction. In response, the animal flexed its head repeatedly to reduce body pitching and physically feel out the terrain. In addition, the animal used two hind legs differentially, extending and depressing one more than the other (P < 0.05, ANOVA), to roll its body to align with the gap between beams to reduce terrain resistance. Finally, the animal pushed the lower hind leg backward on the ground to propel itself forward while flexing its abdomen to break body rubbing against beams. We developed a robot with the ability to flex its head and abdomen and differentially move its legs and used it as a physical model to study the principles of using reactive motions to modulate physical interaction to traverse.