Passive mechanical limb features facilitate rough terrain locomotion of an insect-scale robot.

Insects and robots traversing rugged terrain are aided by mechanical features in the limbs that passively contend with unexpected interactions. Strategies for navigating complex terrain with minimal sensing and computation are needed for small robots, such as the 1.4 g quadrupedal Harvard ambulatory microrobot we previously studied running in open-loop on 3D printed models of complex terrains. We observed two primary sources of performance degradation: colliding with features during the swing phase, which could halt or even reverse forward motion, and jamming of the limb tip in local minima. Including a linear elastic knee joint with a kneecap which allowed only posterior bending allowed the robot to bypass a wall obstacle while still moving effectively on a featureless surface. Performance was sensitive to the elasticity of the hinge, controlled via hinge width. Adding teeth to the front surface of the leg, inspired by the hairs on insect limbs, was necessary for success by allowing the bent limb to provide propulsive forces when in contact with the obstacle. An ant-inspired foot that increased surface area helped prevent the limb tip from getting stuck in small gaps in the terrain. This provides further evidence of the utility of multiscale, multi-modal limb features.