58.3 Thursday, Jan. 5 Legged locomotion of a bio-inspired lightweight robot on granular media QIAN, F*; ZHANG, T; LI, C; SHEN, J; HOOVER, A.M.; BIRKMEYER, P; PULLIN, A; FEARING, R.S.; GOLDMAN, D.I.; MASARATI, P.; Georgia Institute of Technology; Georgia Institute of Technology; Georgia Institute of Technology; Georgia Institute of Technology; F. W. Olin College of Engineering; University of California, Berkeley; University of California, Berkeley; University of California, Berkeley; Georgia Institute of Technology; Politecnico di Milano firstname.lastname@example.org
Many desert-dwelling animals exhibit high locomotor performance on granular media (GM) like sand. Previous studies of a 2 kg legged robot (SandBot) revealed that as limb frequency increased, walking speed increased until a critical frequency above which the robot moved ineffectively. Recently a small, lightweight (10 cm, 25 g) hexapedal robot, dynaRoACH, has begun to approach biological locomotor performance on GM over a wider frequency range. It uses an alternating tripod gait to move at speeds of 50 cm/s at frequencies of 12 Hz. To reveal how dynaRoACH maintains high performance, we use high speed imaging to capture kinematics as the robot moves on a GM of closely packed 3 mm glass particles. We also develop a numerical multi-body model of dynaRoACH coupled to an experimentally validated multi-particle simulation of the GM. Average forward speed in simulation matches experiment and increases non-linearly with stride frequency. The nonlinearity is associated with a change in mode of propulsion. At low frequency dynaRoACH moves like SandBot, using a quasi-static rotary walking mode. During stance, the c-shaped legs rotate about their centers atop solidified grains which kinematically propels the body forward. No aerial phases are observed, and the simulation reveals that vertical ground reaction force (GRF) plateaus during mid-stance. For higher frequencies, dynaRoACH moves dynamically, such that stance duty factor falls below 0.5 and aerial phases occur. Peak vertical GRF occurs at mid stance and increases superlinearly with frequency indicating the importance of inertial forces associated with the acceleration of grains.