IEEE Robotics & Automation Magazine - March 2017 - 47

We tested chassis #7 in an outdoor environment (see
Figure 1), where it navigated uneven terrain with steps up to
approximately 4 cm. Additionally, chassis #7 successfully
demonstrated walking with a failed front-right limb while the
rest of the limbs continued their programmed alternating
tripod gait. These tests demonstrate a promising robustness to
environmental and design uncertainty.
Open-Source Design
We hope to encourage broad use and experimentation
with PARF robots. The reader who wishes to build the
hexapod described herein may find the design files at
https://github.com/BIRDSLab in the BigANT repository
and the pyckbot software library in the pyckbot repository. Assembly tutorial and additional information are in
the video that accompanies this article on IEEE Xplore.
Benefits and Limitations of PARF
PARF mechanisms face limitations with respect to mechanism strength and durability and have difficulty limiting play
over large distances due to local deformations and low tolerances. Both of these issues can be partially overcome with
supporting structures and parallel linkages. As functional
requirements for force and precision become more demanding, PARF designs may be altered to use other materials. In
that case, foam-board PARF mechanisms may still perform
an important role in prototyping.
PARF mechanisms offer a number of advantages compared to metal and hard-plastic mechanisms. With PARF, a
large and useful design space can be explored at a small cost
in time, money, and tooling. Building PARF mechanisms is
approachable for novice designers and is routinely taught to
undergraduates with no mechanical design background. Only
a minimal level of two-dimensional computer-aided design
skill is required, and no knowledge of computer-aided manufacturing. Mechanisms can often be repaired by splinting and
taping, and new features can be prototyped easily and tested
before design files are changed.
We consider the greatest strength of PARF its ability to
create and refine customized robotic mechanisms without
requiring the logistic support structure of a research lab or
industrial research and development department. The
impact of PARF will be greatest for those with access to fewer
resources and a smaller industrial base upon which to rely.
Whether it is rescue workers at a remote disaster site, students learning about robots in a low-income school district,
graduates just out of college founding a robotics start-up
company, a disaster-response team working out of an airdropped container, or the very first humans exploring the
surface of Mars, PARF would allow them to build useful
robots quickly, inexpensively, and with only a few tools.
Acknowledgments
We wish to thank the anonymous reviewers and D. Miller, S.
Fuller, M. Goli, J. Brown, S. Desousa, E. Eklov, D. Litz, A.
Myers, and E. Revzen for contribution to various stages of this

project. This work was supported in part by Army Research
Office grants W911NF-12-1-0284 and W911NF-14-1-0573
to S. Revzen.
References
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Ian Fitzner, University of Michigan, Ann Arbor, Michigan.
E-mail: fitzneri@umich.edu.
Yue Sun, University of Michigan, Ann Arbor, Michigan.
E-mail: heressun@umich.edu.
Vikram Sachdeva, University of Michigan, Ann Arbor, Michigan. E-mail: sachdva@umich.edu.
S. Revzen, University of Michigan, Ann Arbor, Michigan.
E-mail: shrevzen@umich.edu.
March 2017

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Table of Contents for the Digital Edition of IEEE Robotics & Automation Magazine - March 2017
