Meeting Abstract
65.1 Thursday, Jan. 6 Running without feet: the role of tarsi during high-speed horizontal locomotion in cockroaches JAYARAM, K*; MERRITT, C; CHERIAN, A; FULL, R.J.; Univ, of California, Berkeley; Univ, of California, Berkeley; Univ, of California, Berkeley; Univ, of California, Berkeley kaushikj@berkeley.edu
Effective foot-substrate interaction remains a major challenge in the design of legged robots. To understand the contribution of foot-like appendages to the stability of high-speed running on horizontal, hard surfaces, we studied death-head cockroaches, Blaberus discoidalis. Previous studies have demonstrated the importance of tarsal claw engagement for climbing and inverted walking, but, found no change in speed on meshes when the feet or tarsi were removed. We hypothesized that tarsi function as springs to modulate leg force, dampers to dissipate leg-substrate impact energy, and/or stabilizers to mitigate the effects of external perturbations. We compared running performance before and after complete tarsi ablation under three different conditions – flat terrain (n=5, trials=88), rough terrain (n=4, trials=76) and large lateral perturbations (n=3, trials=40). The loss of tarsi on flat terrain did not alter running speed (57.7±13.1 cm/s), stride frequency (16.3±1.5 Hz), duty factor (0.43±0.07) or ground reaction force pattern. Rough terrain locomotion, with perturbations up to three times hip height, produced no difference in running speed (36.2±18.3 cm/s, P>0.1). Neither condition provided evidence for significant force modulation, damping or stabilization. Legs appear to serve these functions. However, when subjected to large lateral perturbations, animals without tarsi were less effective at regaining heading and took longer to attain steady-state body orientation (251.3±32.3 ms) post perturbation compared to those with feet (141.0±27.8 ms). These neuromechanical responses provide new insight on appendage-substrate interactions, inspiring the design of novel feet in the next generation of legged robots.
