Sensitive dependence of the motion of a legged robot on granular media

Legged locomotion on flowing ground ({\em e.g.} granular media) is unlike locomotion on hard ground because feet experience both solid- and fluid-like forces during surface penetration. Recent bio-inspired legged robots display speed relative to body size on hard ground comparable to 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) six-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 two orders of magnitude smaller than the 2 body lengths/s ($\approx 60$ 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 $\phi$ and the limb frequency $\omega$, and a dramatic transition from rotary walking to slow swimming occurs when $\phi$ becomes small enough and/or $\omega$ 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.Comment: 4 figure

RHex: A Biologically Inspired Hexapod Runner

RHex is an untethered, compliant leg hexapod robot that travels at better than one body length per second over terrain few other robots can negotiate at all. Inspired by biomechanics insights into arthropod locomotion, RHex uses a clock excited alternating tripod gait to walk and run in a highly maneuverable and robust manner. We present empirical data establishing that RHex exhibits a dynamical (“bouncing”) gait—its mass center moves in a manner well approximated by trajectories from a Spring Loaded Inverted Pendulum (SLIP)—characteristic of a large and diverse group of running animals, when its central clock, body mass, and leg stiffnesses are appropriately tuned. The SLIP template can function as a useful control guide in developing more complex autonomous locomotion behaviors such as registration via visual servoing, local exploration via visual odometry, obstacle avoidance, and, eventually, global mapping and localization.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44418/1/10514_2004_Article_381456.pd

Dispersion of ventricular repolarization: A new marker of ventricular arrhythmias in patients with rheumatoid arthritis

Objective. To determine the value of dispersion of ventricular repolarization as a diagnostic tool to assess the risk for ventricular arrhythmias in patients with rheumatoid arthritis (RA)

The Response Robotics Summer School 2013: Bringing responders and researchers together to advance Response Robotics

In this paper, we present the 2013 Response Robotics Summer School, an event for the dissemination of the challenges and Best-in-Class capabilities in response robotics, focusing on explosive ordnance disposal and remote handling. A particularly unique feature of this event was the close integration of the responder community in both the technical and practical sessions. This was made possible by co-locating and jointly running this event with the Bomb Response Technology Seminar, an annual workshop for civilian and military bomb squad personnel. This event also builds on a decade-long legacy of response robotics dissemination events. These events leverage the DHS-NIST-ASTM International Standard Test Methods for Response Robots as a common language with which responders, researchers, industry, students and test administrators may communicate their requirements, capabilities and motivations. It builds on the 2012 IEEE-RAS Safety, Security and Rescue Robotics Summer School and sets the stage for the 2014 IEEERAS Response Robotics Summer School

Integrating a Hierarchy of Simulation Tools for Legged Robot Locomotion

Presented at the 2008 IEEE/RSJ International Conference on Intelligent Robots and Systems, IROS 2008, 22-26 Sept. 2008.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