(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.
(Georgia Institute of Technology, 2008-02-29)
Goldman, Daniel I.; Umbanhowar, Paul B.
Direct measurements of the acceleration of spheres and disks impacting granular media reveal simple power law scalings along with complex dynamics which bear the signatures of both fluid and solid behavior. The penetration depth scales linearly with impact velocity while the collision duration is constant for sufficiently large impact velocity. Both quantities exhibit power law dependence on sphere diameter and density, and gravitational acceleration. The acceleration during impact is characterized by two jumps: a rapid, velocity-dependent increase upon initial contact and a similarly sharp depth-dependent decrease as the impacting object comes to rest. Examination of the measured forces on the sphere in the vicinity of these features leads to an experimentally based granular force model for collision. We discuss our findings in the context of recently proposed phenomenological models that capture qualitative dynamical features of impact but fail both quantitatively and in their inability to capture significant acceleration fluctuations that occur during penetration and which depend on the impacted material.