DUDEK, DM*; DASTOOR, S; FULL, RJ; Univ. of California, Berkeley: RAPID RECOVERY FROM AN IMPULSE PERTURBATION TO A LEG IN RUNNING INSECTS

Insects frequently run across unstructured environments, such as leaf litter, with little degradation in performance. Cockroaches rapidly traverse rough terrain with obstacles up to three times their hip height with no detectable change in motor output to major leg muscles when compared to running over smooth, level ground. Previously, we found that the isolated hind leg of a cockroach begins to recover within 5 ms to a vertically directed impulse perturbation. The isolated leg returns to within 99% of its original position within the swing phase duration (< 45 ms). With its vertically oriented joint axes, the response is primarily due to the leg�s passive material properties. To test the response in intact animals, we subjected the hind leg of running cockroaches, Blaberus discoidalis, to vertically directed impulse perturbations during the swing phase by tethering the animal above a Styrofoam ball floating on an air bearing. A beam, actuated by a diaphragm, first slid under the swinging leg and was then lifted upward by a servo-motor to perturb the leg. A point at the distal end of the tibia was tracked at 1000 fps in two views to track the response. As in the isolated leg, the intact leg begins to recover in less than 5 ms, and returns to within the 95% confidence intervals of the original swing trajectory within 40 ms with minimal overshoot. Leg placement at the end of swing was unaffected by the perturbation. Response times improved as perturbations occurred later in swing, recovering in as little as 9 ms. Spring-damping properties of the hind leg may act to simplify control of rapid running over unstructured environments by passively attaining quick settling times with minor overshoot.