GOLDMAN, Daniel I.*; CHEN , Tao C.; FULL, Robert J.; Univ. of California, Berkeley; Univ. of California, Berkeley; Univ. of California, Berkeley: A Template for Rapid Vertical Climbing

Inverted pendulum and spring-mass templates exist for walking and running, respectively, but no such low parameter, general model exists for rapid vertical climbing. Surprisingly, rapid vertical climbing of cockroaches reveal similar dynamics to geckos, despite differences in leg number, morphology and attachment mechanism. During a stride each animal�s center of mass (COM) cyclically accelerates up the wall at a frequency equal to its stepping frequency, while undergoing cyclical lateral accelerations at one-half this frequency. Animals produce these dynamics by generating similar single leg forces. Legs generate forces to pull the animal up the wall with no deceleration as they pull laterally toward the midline. Cockroaches generate the common COM dynamics using an alternating tripod gait. During a step the lateral force developed by the middle leg on one side of the body exceeds the sum of the lateral forces of the front and hind legs on the opposite side of the body. The COM accelerates toward the side of the middle leg stance. Geckos ascend using a trotting gait. During a step the hind leg lateral force exceeds that of the contralateral fore-leg and the COM of the animal accelerates toward the side of hind-leg stance. We model the common COM dynamics as a two degree of freedom system with a rigid mass that cyclically attaches to the wall by a spring in series with an actuator oriented at an angle &beta relative to the body axis. At the beginning of a step, the actuator is maximally displaced while the spring is at rest length. As the actuator decreases length, the spring extends and accelerates the body vertically as well as laterally. This sequence repeats on the contralateral side of the body. We hypothesize that the climbing template allows animals to attain rapid vertical climbing with simple control strategies.