S1-3.13 Jan. 5 Insects Running on Compliant Surfaces SPENCE, Andrew J.*; REVZEN, Shai; YEATES, Kyle; MULLENS, Chris; FULL, Robert J.; Univ. of California, Berkeley; Univ. of California, Berkeley; Univ. of California, Berkeley; Univ. of California, Berkeley; Univ. of California, Berkeley firstname.lastname@example.org
Human runners and hoppers attempt to adjust their leg stiffness to maintain similar center of mass (COM) dynamics when confronted with a compliant substrate. Dynamic materials testing of cockroach legs shows that their behavior in the sagittal plane is largely determined by passive exoskeletal properties. We tested the hypothesis that rapid running cockroaches maintain their COM mechanics by compensating for a compliant substrate. Cockroaches Blaberus discoidalis ran from a rigid Plexiglas surface onto an elastic substrate of stiffness (8-13 N/m) equal to 2/3 its virtual leg spring stiffness (15 N/m for all three legs of a tripod). We directly measured the animalís COM dynamics using a novel 3-axis, MEMs accelerometer configured as a backpack placed near its COM. Vertical acceleration of the COM on the elastic surface had smaller peak-to-peak amplitudes (9.3 ± 0.012 m/s2, n = 374 steps on elastic substrate, vs. 12 ± 0.007 m/s2, n = 879 steps on rigid substrate; p<0.0001). Step duration was slightly longer (44.7 ± 0.044 ms, elastic versus 42.6 ± 0.016 ms rigid; p = 0.019) and forward velocity was actually faster on the elastic substrate (35.6 ± 0.004 cm/s on elastic substrate, versus 33.4 ± 0.002 cm/s on rigid substrate; p < 0.0001). We conclude that the cockroach does not maintain similar vertical accelerations and therefore COM trajectories when encountering an elastic substrate. Despite their inability to maintain constant COM dynamics, cockroaches moved effectively on complaint substrates. Funded by NSF FIBR.