Design Innovation Paper

Soft Spherical Tensegrity Robot Design Using Rod-Centered Actuation and Control

[+] Author and Article Information
Lee-Huang Chen

Mechanical Engineering,
University of California, Berkeley,
Berkeley, CA 94720
e-mail: leehuanc@berkeley.edu

Kyunam Kim, Ellande Tang, Kevin Li, Richard House, Edward Liu Zhu, Kimberley Fountain, Alice M. Agogino

Mechanical Engineering,
University of California, Berkeley,
Berkeley, CA 94720

Adrian Agogino

Intelligent Systems Division,
NASA Ames Research Center,
Mountain View, CA 94035

Vytas Sunspiral

Stinger Ghaffarian Technologies,
Intelligent Systems Division,
NASA Ames Research Center,
Mountain View, CA 94035

Erik Jung

Computer Engineering,
University of California, Santa Cruz,
Santa Cruz, CA 95064

Manuscript received October 17, 2016; final manuscript received February 13, 2017; published online March 9, 2017. Assoc. Editor: Hai-Jun Su.The United States Government retains, and by accepting the article for publication, the publisher acknowledges that the United States Government retains, a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for United States government purposes.

J. Mechanisms Robotics 9(2), 025001 (Mar 09, 2017) (9 pages) Paper No: JMR-16-1318; doi: 10.1115/1.4036014 History: Received October 17, 2016; Revised February 13, 2017

This paper presents the design, analysis, and testing of a fully actuated modular spherical tensegrity robot for co-robotic and space exploration applications. Robots built from tensegrity structures (composed of pure tensile and compression elements) have many potential benefits including high robustness through redundancy, many degrees-of-freedom in movement and flexible design. However, to take full advantage of these properties, a significant fraction of the tensile elements should be active, leading to a potential increase in complexity, messy cable, and power routing systems and increased design difficulty. Here, we describe an elegant solution to a fully actuated tensegrity robot: The TT-3 (version 3) tensegrity robot, developed at UC Berkeley, in collaboration with NASA Ames, is a lightweight, low cost, modular, and rapidly prototyped spherical tensegrity robot. This robot is based on a ball-shaped six-bar tensegrity structure and features a unique modular rod-centered distributed actuation and control architecture. This paper presents the novel mechanism design, architecture, and simulations of TT-3, an untethered, fully actuated cable-driven six-bar spherical tensegrity robot. Furthermore, this paper discusses the controls and preliminary testing performed to observe the system's behavior and performance and is evaluated against previous models of tensegrity robots developed at UC Berkeley and elsewhere.

Copyright © 2017 by ASME
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Fig. 1

TT-2 tensegrity robot with linear actuators

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Fig. 2

NTRT simulations of TT-3 with increasing sequence (a)–(c) of different pretensions

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Fig. 3

A single rod of the tensegrity structure modeled: (a) with a mass at the center of the rod and (b) with two half masses on two ends of the rod. T is the applied torque, m is the rod mass, and r is the rod length.

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Fig. 4

Sequence of impact from the same height of two tensegrity structures with different rod mass distributions

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Fig. 5

Acceleration data of rod-centered TT-3 versus rod-end prototypes during impact in simulation

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Fig. 6

High speed video footage showing the deformation of the TT-3 structure during impact

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Fig. 7

TT-3 deformation from different heights

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Fig. 8

Top and bottom of the actuation module with four motors, a microcontroller, a wireless unit, two motor drivers, a voltage regular, and a battery pack

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Fig. 9

Aluminum tubes, plastic enclosure, actuation module, and enclosure cap on each rod of the TT-3 robot. The actuation module slides into the plastic enclosure.

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Fig. 10

This image displays the top and bottom of the actuation module using the printed circuit board as its base platform

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Fig. 11

TT-3, a six-bar spherical tensegrity robot with cables routed from the center module

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Fig. 12

(a) Cable routed through 3D-printed endcap and (b)machined aluminum endcap

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Fig. 13

Three-dimensional model of the endcap testing platform

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Fig. 14

Plot displaying the relation of tension force on scale 1 and scale 2

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Fig. 15

A conceptual diagram that represents the different stages of shape-shifting performed by TT-3 to complete punctuated rolling

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Fig. 16

(a) A diagram of TT-3 with labeled based triangle T1 and three other neighbor triangles T2, T3, and T4. (b) The diagram displays the three cables C1, C2, C3 and its resulting triangle if actuated [8,10].

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Fig. 17

TT-3 performs straight line walk while carrying a center payload

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Fig. 18

TT-3 performs straight line walk on an uneven outdoor terrain




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