(Georgia Institute of Technology, 2009-03-03)
Li, Chen; Umbanhowar, Paul B.; Komsuoglu, Haldun; Koditschek, Daniel E.; Goldman, Daniel I.
Legged locomotion on flowing ground (e.g., granular media) is unlike locomotion on hard ground because feet experience both solid- and fluid-like forces during surface penetration. Recent bioinspired legged robots display speed relative to body size on hard ground comparable with high-performing organisms like cockroaches but suffer significant performance loss on flowing materials like sand. In laboratory experiments, we study the performance (speed) of a small (2.3 kg) 6-legged robot, SandBot, as it runs on a bed of granular media (1-mm poppy seeds). For an alternating tripod gait on the granular bed, standard gait control parameters achieve speeds at best 2 orders of magnitude smaller than the 2 body lengths/s (≈60 cm/s) for motion on hard ground. However, empirical adjustment of these control parameters away from the hard ground settings restores good performance, yielding top speeds of 30 cm/s. Robot speed depends sensitively on the packing fraction φ and the limb frequency ω, and a dramatic transition from rotary walking to slow swimming occurs when φ becomes small enough and/or ω large enough. We propose a kinematic model of the rotary walking mode based on generic features of penetration and slip of a curved limb in granular media. The model captures the dependence of robot speed on limb frequency and the transition between walking and swimming modes but highlights the need for a deeper understanding of the physics of granular media.
(Georgia Institute of Technology, 2008-09)
Slatton, Andrew; Cohen, Daniel; Ding, Yang; Umbanhowar, Paul B.; Goldman, Daniel I.; Haynes, G. Clark; Komsuoglu, Haldun; Koditschek, Daniel E.
We are interested in the development of a variety
of legged robot platforms intended for operation in
unstructured outdoor terrain. In such settings, the traditions of
rational engineering design, driven by analytically informed and
computationally assisted studies of robot-environment models,
remain ineffective due to the complexity of both the robot
designs and the terrain in which they must operate. Instead,
empirical trial and error often drives the necessary incremental
and iterative design process, hence the development of such
robots remains expensive both in time and cost, and is often
closely dependent upon the substrate properties of the locomotion
terrain. This paper describes a series of concurrent but
increasingly coordinated software development efforts that aim
to diminish the gap between easily interfaced and physically
sound computational models of a real robot’s operation in a
complex natural environment. We describe a robot simulation
environment in which simple robot modifications can be easily
prototyped along and “played” into phenomenological models
of contact mechanics. We particularly focus on the daunting
but practically compelling example of robot feet interacting
granular media, such as gravel or sand, offering a brief report
of our progress in deriving and importing physically accurate
but computationally tractable phenomenological substrate models
into the robot execution simulation environment. With a
goal of integration for future robot prototyping simulations,
we review the prospects for diminishing the gap between the
integrated computational models and the needs of physical
platform development.