Meeting Abstract
93.3 Monday, Jan. 6 14:00 Effect of friction on cockroaches running in confined spaces JAYARAM, K*; GOLDMAN, D; FULL, R J; Univ. of California, Berkeley; Georgia Institute of Tech.; Univ. of California, Berkeley kaushikj@berkeley.edu
Cockroaches, Periplaneta americana, run through confined spaces (4-12 mm) less than a third of their standing height using their compression exoskeleton. We hypothesized that limit on the smallest traversable gap could be determined by the animal’s ability to generate effective force production driving forward motion. To test the importance of force limitations, we changed the friction on the ceiling (top) and running surface (bottom) of a variable ceiling height rectangular tunnel at gap heights of 4, 6, 9, 12mm. For the top surface, we used uncoated Plexi-glas, P40 grit sandpaper and graphite powder as control, high, and low friction surfaces, respectively. Increasing friction on the top surface decreased running speeds of animals across all gap heights by 5-40% with the greatest decrease at the smallest gap. Decreased speed resulted from a decrease in stride length and a more tortuous path. Decreasing friction did not show any significant change in performance. For the bottom surface, we used Plexi-glas lined with P40, P20, and P100 grit sandpaper as control, high, and low friction surfaces, respectively. Increasing friction did not change performance at 6, 9 or 12mm, but produced decreased speeds at 4mm gaps. The decrease in speed resulted from a decrease in stride length accompanied by increased slipping. Decreasing friction did not change performance at 9 or 12mm, but resulted in discontinuous motion with frequent foot slippage at 4 and 6mm. A simple theoretical model suggests that modifying the spring loaded inverted pendulum-like motion typical of unrestricted locomotion imposes significant forces on the body in confined environments that hinders forward locomotion. The effect of friction in confined spaces is assisting the design of compressible legged robots that can assist in search-and-rescue.
