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2017 | OriginalPaper | Chapter

Core Actuation Promotes Self-manipulability on a Direct-Drive Quadrupedal Robot

Authors : Jeffrey Duperret, Benjamin Kramer, Daniel E. Koditschek

Published in: 2016 International Symposium on Experimental Robotics

Publisher: Springer International Publishing

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Abstract

For direct-drive legged robots operating in unstructured environments, workspace volume and force generation are competing, scarce resources. In this paper we demonstrate that introducing geared core actuation (i.e., proximal to rather than distal from the mass center) increases workspace volume and can provide a disproportionate amount of work-producing-force to the mass center without affecting leg linkage transparency. These effects are analytically quantifiable up to modest assumptions, and are demonstrated empirically on a spined quadruped performing a leap both on level ground and from an isolated foothold (an archetypal feature of unstructured terrain).

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previous chapter Experimental Evaluation of a Perceptual Pipeline for Hierarchical Affordance Extraction
next chapter Experiments with Hierarchical Reinforcement Learning of Multiple Grasping Policies
Appendix
Available only for authorised users
Footnotes
5
This imparted a pitching moment on the body that improved the landing.
 
6
This assumes that all the leg motors operate at near constant torque, which is often a reasonable assumption for direct-drive legged-robot motors given their typical low-speed, torque-limited regime of operation. In these experiments, the motor torque is limited by the power electronics’s 43 A maximum current output, so a U8-16 motor being driven at 12 V hits the speed-torque curve and becomes power-limited when rotating faster than 42 rad/sec. The maximum angular velocity observed on the leg motors was less than 30 rad/sec, so the leg motors never leave their low-speed torque-limited regime of operation.
 
7
Unlike the legs, the spine motors see speeds as high as 62 rad/sec and thus transition from being torque-limited by the power electronics to being limited by the speed-torque curve. At such high speeds, the maximum torque output is \(76\,\%\) of the maximum leg torque output. Increasing the voltage driving the motors would diminish this torque loss.
 
8
This benefit is doubled when accounting for the fact that the spine can both extend on liftoff and retract on landing to perform useful work over the course of a leap or stride, unlike a leg motor.
 
9
An established metric for evaluating the ability of a direct-drive limb to generate forces is thermal cost of force (for a normalized motor constant) given by the mean of the squared singular values of the forward kinematic Jacobian [14, page 48], [3]. As shown in the analysis above, in general smaller singular values are achievable by decreasing the length of lever arms in the (possibly parallel) kinematic chain to gain a greater mechanical advantage.
 
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Metadata
Title
Core Actuation Promotes Self-manipulability on a Direct-Drive Quadrupedal Robot
Authors
Jeffrey Duperret
Benjamin Kramer
Daniel E. Koditschek
Copyright Year
2017
Book
2016 International Symposium on Experimental Robotics

Print ISBN: 978-3-319-50114-7

Electronic ISBN: 978-3-319-50115-4

Copyright Year: 2017

DOI
https://doi.org/10.1007/978-3-319-50115-4_14