Lynch, Goran A
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Publication Dynamic Vertical Climbing: Bioinspiration, Design, and Analysis(2011-12-21) Lynch, GoranBiologists have proposed a pendulous climbing model, the Full-Goldman (F-G) template, that abstracts remarkable similarities in dynamic wall scaling behavior exhibited by radically different animal species. This thesis presents a progression of work related to dynamic vertical climbing based on that model. We begin by describing the inspiration, design, implementation of and experimentation with the first dynamical vertical climbing robot. We study numerically a version of the pendulous climbing template dynamically re-scaled for applicability to utilitarian payloads with conventional electronics and actuation, revealing that the incorporation of passive compliance can compensate for an artifact’s poorer power density and scale disadvantages relative to biology. However, the introduction of these dynamical elements raises new concerns about stability regarding both the power stroke and limb coordination that we allay via mathematical analysis. Combining these numerical and analytical insights into a series of design prototypes, we document the correspondence of the various models to the variously scaled platforms and report that our approximately two kilogram platform, DynoClimber, climbs dynamically at vertical speeds up to 1.5 bodylengths per second — in particular, the final 2.6 kg prototype climbs at an average steady state speed of 0.66 m/s against gravity on a carpeted vertical wall, in rough agreement with our various models’ predictions. We establish whether the success of the robot is inherent to the morphology suggested by the F-G template or, instead, to a fortuitous set of parameter choices during the robot’s design. Thus we examine the effects of (i) actuator dynamics and (ii) lateral force generation on climber stability by investigating a sequence of reduced order variants of the F-G template. We prove analytically that a purely vertical climber is stable for a general class of actuator force functions, and use that result to further simplify our models by allowing the prescription of leg length. We use that simplification to demonstrate that a sprawled posture stabilizes vertical climbing by damping rotational motion during stride transitions. We also notably demonstrate through simulation that a climber’s stability does not depend on the actuation frequency it employs. Finally, we explore the potential benefits of pendulous dynamical climbing in animals and in robots by examining the stability and power advantages of variously more and less sprawled limb morphologies when driven by conventional motors in contrast with animal-like muscles. For quadratic-in-velocity power output actuation models typical of commercially available electromechanical actuators, our results suggest the new hypothesis that sprawled posture may confer significant energetic advantage. In notable contrast, muscle-powered climbers do not experience an energetic benefit from sprawled posture due to their sufficiently distinct actuator characteristics and operating regimes. These results suggest that the benefits of sprawled posture climbing may be distinctly different depending upon the details of the climber’s sensorimotor endowment. This study also shows that even minimally intelligent foot placement improves stability when compared to the template-derived rigid sprawl.Publication Rapid Pole Climbing with a Quadrupedal Robot(2009-05-01) Haynes, G C; Lynch, Goran; Khripin, Alex; Amory, Jon; Koditschek, Daniel E; Saunders, Aaron; Rizzi, Alfred AThis paper describes the development of a legged robot designed for general locomotion of complex terrain but specialized for dynamical, high-speed climbing of a uniformly convex cylindrical structure, such as an outdoor telephone pole. This robot, the RiSE V3 climbing machine—mass 5.4 kg, length 70 cm, excluding a 28 cm tail appendage—includes several novel mechanical features, including novel linkage designs for its legs and a non-backdrivable, energy-dense power transmission to enable high-speed climbing. We summarize the robot’s design and document a climbing behavior that achieves rapid ascent of a wooden telephone pole at 21 cm/s, a speed previously unachieved—and, we believe, heretofore impossible—with a robot of this scale. The behavioral gait of the robot employs the mechanical design to propel the body forward while passively maintaining yaw, pitch, and roll stability during climbing locomotion. The robot’s general-purpose legged design coupled with its specialized ability to quickly gain elevation and park at a vertical station silently with minimal energy consumption suggest potential applications including search and surveillance operations as well as ad hoc networking.Publication Sprawl Angle in Simplified Models of Vertical Climbing: Implications for Robots and Roaches(2010-10-01) Lynch, Goran A.; Rome, Lawrence; Koditschek, Daniel EEmpirical data taken from fast climbing sprawled posture animals reveals the presence of strong lateral forces with significant pendulous swaying of the mass center trajectory in a manner captured by a recently proposed dynamical template. In this simulation study we explore the potential benefits of pendulous dynamical climbing in animals and in robots by examining the stability and power advantages of variously more and less sprawled limb morphologies when driven by conventional motors in contrast with animal-like muscles. For open loop models of gait generation inspired by the neural-deprived regimes of high stride-frequency animal climbing, our results corroborate earlier hypotheses that sprawled posture may be required for stability. For quadratic-in- velocity power output actuation models typical of commercially available electromechanical actuators, our results suggest the new hypothesis that sprawled posture may confer significant energetic advantage. In notable contrast, muscle-powered climbers do not experience an energetic benefit from sprawled posture due to their sufficiently distinct actuator characteristics and operating regimes. These results suggest that the potentially significant benefits of sprawled posture climbing may be distinctly different depending upon the details of the climber's sensorimotor endowment. They offer a cautionary instance against mere copying of biology by engineers or rote study of physical models by biologists through this reminder of how even simple questions addressed by simple models can yield nuanced answers that only begin to hint at the complexity of biological designs and behaviors.Publication X-RHex: A Highly Mobile Hexapedal Robot for Sensorimotor Tasks(2010-11-04) Galloway, Kevin C; Haynes, Galen Clark; Ilhan, B. Deniz; Johnson, Aaron M; Knopf, Ryan; Lynch, Goran A; Plotnick, Benjamin N; White, Mackenzie; Koditschek, Daniel EWe report on the design and development of X-RHex, a hexapedal robot with a single actuator per leg, intended for real-world mobile applications. X-RHex is an updated version of the RHex platform, designed to offer substantial improvements in power, run-time, payload size, durability, and terrain negotiation, with a smaller physical volume and a comparable footprint and weight. Furthermore, X-RHex is designed to be easier to build and maintain by using a variety of commercial off-the-shelf (COTS) components for a majority of its internals. This document describes the X-RHex architecture and design, with a particular focus on the new ability of this robot to carry modular payloads as a laboratory on legs. X-RHex supports a variety of sensor suites on a small, mobile robotic platform intended for broad, general use in research, defense, and search and rescue applications. Comparisons with previous RHex platforms are presented throughout, with preliminary tests indicating that the locomotive capabilities of X-RHex can meet or exceed the previous platforms. With the additional payload capabilities of X-RHex, we claim it to be the first robot of its size to carry a fully programmable GPU for fast, parallel sensor processing.