Mechanically Mediated Rapid Transitions

We marvel at the gracefulness of large animals as they maneuver over complex terrain with barely a miss-step. Small animals appear to have alternative strategies that rely on the properties of their skeletal system that we should consider no less elegant. To elucidate these strategies, we used high-speed video to record horizontal to vertical transitions in the cockroach Periplaneta americana. After eliciting an escape response, animals ran down a trackway at 18 to 43 body lengths/s toward a vertical wall. In 80% of the trials (n=43) animals successfully made the transition. In 60% of the successful transitions, the animal collided with the wall head-first and then reared upward using primarily hind-leg extension. In the other 40% of the successful transitions, animals adopted a high-angle body posture that avoided head-on collisions, but still relied on energy absorption by the head and/or front legs. Successful head-on collision transitions occurred at a faster range of speeds (65-129 cm/s) than non-head-on collisions (54-78 cm/s). Surprisingly, these two strategies showed no significant difference in the average time from wall contact to vertical posture (73±7 SE ms). We found no significant differences in strategies or performance across individuals, lighting conditions, or substrate properties. Our results suggest that when pressed to extreme performance involving severe bandwidth and/or computational limitations from the nervous system, small animals can rely on the mechanical properties of their body and appendages to sustain large impulses and thus simplify task-level control. This principle of bio-mechanical robustness has inspired the design of novel robots that use energy-absorbing exoskeletons to complete challenging maneuvers.

Publications

Jayaram, K., Mongeau, J.-M., McRae, B., Full, R.J. High-Speed Horizontal to Vertical Transitions in Running Cockroaches Reveals a Principle of Robustness, SICB Annual Meeting 2010, Seattle, January 3-7, 2010.

Press

Science News: Racing Crash-Happy Cockroaches, Science Meeting Briefs, Elizabeth Pennisi, 12 February 2010, Vol 327 Science. p 776.