Research Papers

A Three-Dimensional Printed, Nonassembly, Passive Dynamic Walking Toy: Design and Analysis

[+] Author and Article Information
Christian L. Treviño

Robotics and Motion Laboratory,
Department of Mechanical Engineering,
The University of Texas at San Antonio,
One UTSA Circle,
San Antonio, TX 78249

Joseph D. Galloway, II

Robotics and Motion Laboratory,
Department of Mechanical Engineering,
The University of Texas at San Antonio,
One UTSA Circle,
San Antonio, TX 78249

Pranav A. Bhounsule

Robotics and Motion Laboratory,
Department of Mechanical Engineering,
The University of Texas at San Antonio,
One UTSA Circle,
San Antonio, TX 78249
e-mail: pranav.bhounsule@utsa.edu

1Corresponding author.

Contributed by the Mechanisms and Robotics Committee of ASME for publication in the JOURNAL OF MECHANISMS AND ROBOTICS. Manuscript received July 16, 2017; final manuscript received June 6, 2018; published online September 21, 2018. Assoc. Editor: Sarah Bergbreiter.

J. Mechanisms Robotics 10(6), 061009 (Sep 21, 2018) (8 pages) Paper No: JMR-17-1211; doi: 10.1115/1.4040634 History: Received July 16, 2017; Revised June 06, 2018

In this paper, we present the redesign and analysis of a century old walking toy. Historically, the toy is made up of two wooden pieces including a rear leg and a front leg and body (as a single piece) that are attached to each other by means of a pin joint. When the toy is placed on a ramp and given a slight perturbation, it ambles downhill powered only by gravity. Before the toy can walk successfully, it needs careful tuning of its geometry and mass distribution. The traditional technique of manual wood carving offers very limited flexibility to tune the mass distribution and geometry. We have re-engineered the toy to be three-dimensional (3D) printed as a single integrated assembly that includes a pin joint and the two legs. After 3D printing, we have to manually break-off the weakly held support material to allow movement of the pin joint. It took us 6 iterations to progressively tune the leg geometry, mass distribution, and hinge joint tolerances to create our most successful working prototype. The final 3D printed toy needs minimal postprocessing and walks reliably on a 7.87 deg downhill ramp. Next, we created a computer model of the toy to explain its motion and stability. Parameter studies reveal that the toy exhibits stable walking motion for a fairly wide range of mass distributions. Although 3D printing has been used to create nonassembly articulated kinematic mechanisms, this is the first study that shows that it is possible to create dynamics-based nonassembly mechanisms such as walking toys.

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Fig. 1

Wilson Walkie [1]: (a) front view, (b) side view, and (c) A 3D printed Wilson Walkie and wooden toy in the inset [2]

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Fig. 2

Ravert toy: (a) perspective view, (b) toy duck, and (c) section view of the toy duck (taken from [3])

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Fig. 3

The final working prototype

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Fig. 4

Sectional view of the design: (a) hinge design with tolerances. All dimensions are in cm. Shaded areas represent hollow sections; (b) in-fill pattern created by CURA, the postprocessing software for the 3D printer.

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Fig. 5

Robot model for simulation

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Fig. 6

Sequence of phases and transitions used for simulation model: a single and doubled curved arrow on the figure indicates that the toy is a one or two degree-of-freedom system in that particular phase

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Fig. 7

Phase portrait for the front and rear leg. See corresponding letters in Fig. 7 and Eq. (1).

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Fig. 8

Comparing simulation with experimental data. Positions of various points on the toy as a function of time. (a) Pin joint, (b) bottom corner of the front foot (nearest to the rear foot), and (c) bottom corner of the rear foot (nearest to the front foot).

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Fig. 9

A single step of the walker: (top panel) One step from video. (Bottom panel) Animation from the simulation. See the video online for a comparison.3

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Fig. 10

Effect of varying r, w1, and c1 on maximum eigenvalue and velocity. (a)–(c) Maximum eigenvalue and (d)– (f) velocity nondimensionalized by gr. Each parameter r, w1, and c1 is nondimensionalized by its nominal parameter given in Table 1. The values for our design are shown using a black dot.



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