Technical Briefs

Mini Twist: A Study of Long-Range Linear Drive by String Twisting

[+] Author and Article Information
James J. Guzek

Mechanical and Aerospace Engineering,  Cornell University, Ithaca, NY 14853jjg45@cornell.edu

Conrad Petersen

Mechanical and Aerospace Engineering,  Cornell University, Ithaca, NY 14853ctp32@cornell.edu

Stephane Constantin

Electrical and Computer Engineering,  Cornell University, Ithaca, NY 14853sc445@cornell.edu

Hod Lipson

Electrical and Computer Engineering, Computing and Information Science,  Cornell University, Ithaca, NY 14853hod.lipson@cornell.edu

J. Mechanisms Robotics 4(1), 014501 (Feb 03, 2012) (7 pages) doi:10.1115/1.4005331 History: Received February 24, 2010; Revised September 22, 2011; Published February 03, 2012; Online February 03, 2012

Published methods of linear actuation via string transmission are discussed. A novel twisting string actuator design named Mini Twist is introduced. The design and components of the Mini Twist are thoroughly explained, and a theoretical model for its transmission method is discussed. The experimental set-up is defined. Experimental data regarding the relationship between string diameter, string tension, strand count, and strand type is presented, and analysis of the data is provided. The features of the actuator and the validity of the theoretical model are summarized.

Copyright © 2012 by American Society of Mechanical Engineers
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Figure 1

Linear twist actuator: (a) fully assembled twist actuator; (b) exploded diagram of twist actuator case

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Figure 2

Assembly of twist actuator components: (a) actuator casing body. Note the strain gauge plate in the back. (b) Assembled actuator casing, with optical encoder on nozzle. Pictured with quarter. (c) PCB, blue PCB cover, and bottom of actuator showing screw holes. (d) Fully assembled actuator, with optical encoder cap. Twist ties hold loose wires tightly to the actuator through holes in the body, located below the battery compartment.

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Figure 3

Visual representations of geometric aspects of a twisted cord: (a) cross section of a bundle of strands; (b) flattened representation of a single helical twist

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Figure 4

Strand packing diagrams for various numbers of strings

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Figure 5

Plots of actuator data: (a) graph of number of motor turns versus string length for a variety of tensions, for a strand of 0.0838 cm diameter. (b) Graph of length of string versus number of turns of motor for strings with different numbers of strands, but fixed tension for string of 0.1067 cm diameter. (c) Graph of string length versus number of turns for strings with different strand diameter, but fixed strand number and tension. (d) Graph of length of string versus number of turns of motor for different strand types.

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Figure 6

Cube robot at different angles: (a) cube leaning left; (b) cube upright, with both strings of equal length; (c) cube leaning right

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Figure 7

Electrical schematic for actuator circuit board




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