GOLDMAN, D.I.*; FULL, R.J.; University of California, Berkeley: Dynamics of Rapid Vertical Climbing in Hexapods

A general model for rapid, dynamic legged climbing is emerging. Despite differences in morphology, the single leg ground reaction force patterns of climbing cockroaches were remarkably similar to that discovered in geckos. We measured these forces in the cockroach Blaberus discoidalis (n = 5; 2.1 &plusmn 0.4 g) during rapid vertical climbs (17.5 &plusmn 4.2 cm/sec, approximately 10 BL/sec) using a miniature force platform. To ensure reliable foot-surface contact at each step, we coated aluminum plates with a monolayer of 700 μm glass beads. This rough surface allowed the tarsal claws and pads to easily engage and disengage. Fore and hind limbs generated wall reaction forces in the direction away from the midline of the body. Pulling inward appeared to assist in engaging the attachment mechanisms. To counter potential pitch-back, the fore limbs pulled the head toward the wall at each step, while the hind limbs pushed the abdomen away from the wall. All legs generated forces that pulled the animal upwards. To better define key parameters of climbing, we designed a minimal feed-forward, hexapedal, climbing model. We discovered that when compliances, damping, tarsal stiffness, leg trajectory/timing are tuned appropriately, the tarsal-wall forces during rapid climbing resembled those of the animals. Supported by DARPA M000219 and DCI NMA501-03.