Walking and Running on Yielding and Fluidizing Ground

Feifei Quan, Georgia Institute of Technology - Main Campus
Tingnan Zhang, Georgia Institute of Technology - Main Campus
Chen Li, Georgia Institute of Technology - Main Campus
Pierangelo Masarati, Politecnico di Milano
Aaron M. Hoover, Franklin W. Olin College of Engineering
Paul Birkmeyer, University of California - Berkeley
Andrew Pullin, University of California - Berkeley
Ronald S. Fearing, University of California - Berkeley
Daniel I. Goldman, Georgia Institute of Technology - Main Campus

© 2012 MIT Press. This article was published in the proceedings of Robotics: Science and Systems VIII, and can be found here.


We study the detailed locomotor mechanics of a small, lightweight robot (DynaRoACH, 10 cm, 25 g) which can move on a granular substrate of closely packed 3 mm diameter glass particles at speeds up to 50 cm/s (5 body length/s), approaching the performance of small, high-performing, desert-dwelling lizards. To reveal how the robot achieves this high performance, we used high speed imaging to capture kinematics, and developed a numerical multi-body simulation of the robot coupled to an experimentally validated discrete element method (DEM) simulation of the granular media. Average forward speeds measured in both experiment and simulation agreed well, and increased non-linearly with stride frequency, reflecting a change in the mode of propulsion. At low frequencies, the robot used a quasi-static “rotary walking” mode, in which the granular material yielded as the legs penetrated and then solidified once vertical force balance was achieved. At high frequencies, duty factor decreased below 0.5 and aerial phases occurred. The propulsion mechanism was qualitatively different: the robot ran rapidly by utilizing the speed-dependent fluid-like inertial response of the material. We also used our simulation tool to vary substrate parameters that were inconvenient to vary in experiment (e.g., granular particle friction) to test performance and reveal limits of stability of the robot. Using small robots as physical models, our study reveals a mechanism by which small animals can achieve high performance on granular substrates, which in return advances the design and control of small robots in deformable terrains.