The Effect of Leg Specialization in a Biomimetic Hexapedal Running Robot

[+] Author and Article Information
Jonathan E. Clark

Department of ESE, University of Pennsylvania, Philadelphia, PA 19104jonclark@seas.upenn.edu

Mark R. Cutkosky

Department of Mechanical Engineering, Stanford University, Stanford, CA 94305

The interested reader can view a clip of the high-speed video (250framess) superimposed on the animated model at the following URL: http://dart.stanford.edu:88/Get/File-442/blenḏlight.mov.

J. Dyn. Sys., Meas., Control 128(1), 26-35 (Dec 01, 2005) (10 pages) doi:10.1115/1.2168477 History: Received April 01, 2005; Revised December 01, 2005

The biologically inspired Sprawl family of hexapedal robots has shown that fast and stable running is possible with only open-loop control. Proper design of the passively self-stabilizing leg structure has enabled these robots to run at speeds of up to 15 bodylengths/s and over uneven terrain. Unlike other running robots built to date, the Sprawl robots’ front and rear legs are designed to preform distinct functional roles. Like the cockroaches that inspired them, the front legs of the robots act to lift and decelerate, while the rear legs provide the primary forward thrust. This paper uses a dynamic simulation to investigate the effect that changing the robot’s leg structure and posture has on its performance. The simulation results support our hypothesis that the use of a differential leg function induced through postural adjustments effectively trades efficiency for stability.

Copyright © 2006 by American Society of Mechanical Engineers
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Figure 1

Functional design principles adapted from biomechanical analysis of running cockroaches

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Figure 2

(A) Overview of the hop model and (B) the step deflection response for both the robot leg and the model

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Figure 3

A comparison of the pressure rise and ground reaction force for (A) the robot leg and (B) model

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Figure 4

Ground reaction forces for each leg of the robot and the model

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Figure 5

Effect of leg angle on the velocity of Outdoor Sprawl. Each grid location represents a different nominal configuration of the robot. Each point is where the lines of action of the legs intersect. The circle radius at each point is proportional to the velocity at that configuration. The shaded area represents the unstable operating regime.

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Figure 6

Effect of altering hip stiffness on velocity for a range of leg angles: (A) for the softest hips tested, (B) for optimal stiffness selected in Sec. 5, and (C) for the stiffest value tested. (D) Shows the peak velocity for all configurations at each level of stiffness tested, (E) shows the fraction of the tested configurations at each stiffness that resulted in fast, period-1 running.

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Figure 7

Effect of leg configuration on the model’s velocity (A) and the on band of slopes that it can traverse (B)

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Figure 8

Effect of leg configuration on fore-aft (A) and pitch (B) perturbation settling times

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Figure 9

Comparison of the effect of leg posture for four different stability measures considered in this chapter. The circles represent the velocity at stable configurations.

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Figure 10

Whole body and individual leg ground reaction forces for the Narrow and Sprawled configurations of the model




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