Abstract

Full, R.J., Tu, M.S. and Ting, L. 1989. Dynamics of insect locomotion compared to hexapod walking machine models. Proc. Amer. Soc. Mech. Engineering DSC 17, 35-40.

Arthropods, such as insects and crabs, have served as models for the mechanical design of legged vehicles. Yet surprisingly little is known about the kinetics and kinematics of arthropod locomotion - only gait patterns have been analyzed extensively. We used a miniature force plate to measure the ground reaction forces of two cockroaches, Blaberus discoidalis (mass: 2.6 g) and Periplaneta americana (mass = 0.83 g). A video camera along with a 3'dimensional motion analysis system was used to determine kinematic variables. Cockroaches used an alternating tripod gait between 0.14 and 1.0 m/s. At the highest speeds P. americana became bipedal, using only its rear legs. Aerial phases were observed in P. amencana at speeds near 1.5 m/s. Patterns of total ground reaction force produced by sixlegged cockroaches were remarkably similar to those produced by two, four and eight-legged runners. Fluctuations in potential and horizontal kinetic energy of the center of mass were in phase as predicted by models of running or bouncing gaits. Calculation of Froude numbers and analysis of the vertical force pattern's shape support the use of a bouncing gait. The rate of external work increased linearly with speed, except at the very highest speeds. The mass-specific mechanical energy used to move the center of mass a given distance (1.0 J/m/kg) was similar to that produced by ghost crabs, mammals and birds. Similarities in force patterns, stride frequency, and mechanical energy production suggest common design in animals varying in leg number, style of locomotion, and skeletal type. Modelling the actual dynamics of insect running could lead to improved designs for legged vehicles.