Using an insect-scale robot to explore the impact of limb number and length on locomotion in unstructured terrain.

Hexapod insects and quadruped lizards ably traverse unstructured terrains. Using quadruped and hexapod versions of the insect-scale Harvard Ambulatory Microrobot as a robophysical model, we endeavored to elucidate how limb morphology and kinematics impact locomotor performance in rugged terrain as a function of the number of limbs. Guided by our previous work studying passive compliant limbs in small-scale locomotors, we varied the amount of the limb in contact with the substrate by incorporating passive joints to partially collapse the limb. We placed pairs of limbs of different lengths on the robots and measured speed and mechanical cost-of-transport as they traversed a 3D printed terrain with randomized feature heights. We tested the hexapod using an alternating tripod gait and the quadruped using both a walk—the quadrupedal analog to the alternating tripod—and a trot. We included limb and gait combinations which result in body-terrain contact to explore whether using the body as an additional point of support could help ensure robust locomotion.