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ItemMarch of the SandBots(Georgia Institute of Technology, 2009-04) Goldman, Daniel I. ; Komsuoglu, Haldun ; Koditschek, Daniel E.Goldman at Georgia Tech, Koditschek and Komsuoglu at the University of Pennsylvania, in Philadelphia, and other collaborators - are hoping that by studying the zebra-tailed lizard and a menagerie of other desert-dwelling creatures, we can create more agile versions of their six-legged robot, SandBot.
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ItemSensitive dependence of the motion of a legged robot on granular media(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.
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ItemIntegrating a Hierarchy of Simulation Tools for Legged Robot Locomotion(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.
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ItemScaling and Dynamics of Sphere and Disk Impact into Granular Media(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.
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ItemDesign of a Bio-inspired Dynamical Vertical Climbing Robot(Georgia Institute of Technology, 2008) Clark, Jonathan E. ; Goldman, Daniel I. ; Lin, Pei-Chun ; Lynch, Goran ; Chen, Tao S. ; Komsuoglu, Haldun ; Full, Robert J. ; Koditschek, Daniel E.This paper reviews a template for dynamical climbing originating in biology, explores its stability properties in a numerical model, and presents emperical data from a physical prototype as evidence of the feasibility of adapting the dynamics of the template to robot that runs vertically upward. The recently proposed pendulous climbing model abstracts remarkable similarities in dynamic wall scaling behavior exhibited by radically different animal species. The present paper’s first contribution summarizes a numerical study of this model to hypothesize that these animals’ apparently wasteful commitments to lateral oscillations may be justified by a significant gain in the dynamical stability and, hence, the robustness of their resulting climbing capability. The paper’s second contribution documents the design and offers preliminary empirical data arising from a physical instantiation of this model. Notwithstanding the substantial differences between the proposed bio-inspired template and this physical manifestation, initial data suggest the mechanical climber may be capable of reproducing both the motions and ground reaction forces characteristic of dynamical climbing animals. Even without proper tuning, the robot’s steady state trajectories manifest a substantial exchange of kinetic and potential energy, resulting in vertical speeds of 0.30 m/s (0.75 bl/s) and claiming its place as the first bio-inspired dynamical legged climbing platform.
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ItemSignatures of glass formation in a fluidized bed of hard spheres(Georgia Institute of Technology, 2006-04-14) Goldman, Daniel I. ; Swinney, Harry L.We demonstrate that a fluidized bed of hard spheres during defluidization displays properties associated with formation of a glass. The final state is rate dependent, and as this state is approached, the bed exhibits heterogeneity with increasing time and length scales. The formation of a glass results in the arrest of macroscopic particle motion and thus the loss of fluidization. Microscopic motion persists in this state, but the bed can be jammed by application of a small increase in flow rate. Thus a fluidized bed can serve as a test system for studies of glass formation and jamming.
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ItemToward a dynamic climbing robot(Georgia Institute of Technology, 2006) Clark, Jonathan E. ; Goldman, Daniel I. ; Chen, Tao S. ; Full, Robert J. ; Koditschek, Daniel E.Simple mathematical models or ‘templates’ of locomotion have been effective tools in understanding how animals move and have inspired and guided the design of robots that emulate those behaviors. This paper describes a recently proposed biologically-based template for dynamic vertical climbing, and evaluates the feasibility of adapting it to build a vertical ‘running’ robot. We present the results a simulation study suggesting that appropriate mechanical and control alterations to the template result in fast stable climbing that preserves the characteristic body motions and foot forces found in the template model and in animals. These design changes should also allow the robot to operate with commercially available actuators and in the same power to weight range as other running and climbing robots.
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ItemThe RiSE Climbing Robot: Body and Leg Design(Georgia Institute of Technology, 2006) Saunders, Aaron ; Goldman, Daniel I. ; Full, Robert J. ; Buehler, MartinThe RiSE robot is a biologically inspired, six legged climbing robot, designed for general mobility in scansorial (vertical walls, horizontal ledges, ground level) environments. It exhibits ground reaction forces that are similar to animal climbers and does not rely on suction, magnets or other surface-dependent specializations to achieve adhesion and shear force. We describe RiSE’s body and leg design as well as its electromechanical, communications and computational infrastructure. We review design iterations that enable RiSE to climb 90o carpeted, cork covered and (a growing range of) stucco surfaces in the quasi-static regime.
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ItemStationary state volume fluctuations in a granular medium(Georgia Institute of Technology, 2005-03-30) Schroeter, Matthias ; Goldman, Daniel I. ; Swinney, Harry L.A statistical description of static granular material requires ergodic sampling of the phase space spanned by the different configurations of the particles. We periodically fluidize a column of glass beads and find that the sequence of volume fractions ϕ of postfluidized states is history independent and Gaussian distributed about a stationary state. The standard deviation of ϕ exhibits, as a function of ϕ, a minimum corresponding to a maximum in the number of statistically independent regions. Measurements of the fluctuations enable us to determine the compactivity X, a temperaturelike state variable introduced in the statistical theory of Edwards and Oakeshott [Physica A 157, 1080 (1989)].
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ItemRobotics in Scansorial Environments(Georgia Institute of Technology, 2005) Autumn, Kellar ; Buehler, Martin ; Cutkosky, Mark ; Fearing, Ronald S. ; Full, Robert J. ; Goldman, Daniel I. ; Groff, Richard ; Provancher, William ; Rizzi, Alfred E. ; Saranli, Uluc ; Saunders, Aaron ; Koditschek, Daniel E.