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software because of the difficulties encountered when replicating
physical components as opposed to using and modifying
code. Researchers often choose to purchase commercially
available, expensive, closed source hardware that is hard
to modify, repair, and maintain, or dedicate resources and
time to creating their own hardware from the ground up. But
recent advancements in rapid prototyping (e.g., 3D printing
and laser or waterjet cutting) have enabled mechanical
fabrication with minimal specialized expertise, easy-to-use
equipment, and at relatively low cost, especially compared
to alternatives such as computerized numeric control (CNC)
machining. These technologies, although still in their infancy,
have made it so that many parts can be fabricated with
sufficient durability and mechanical strength to be functionally
used in a range of robotics applications. As a result,
building an open source mechanical hardware project has
become much more feasible, and there are now a range of
high-quality open source hardware projects that create new
technologies and deliver impact to the robotics community.
The objective of this review is to highlight such robot hardware
by identifying the key characteristics and effective
development practices, surveying widely adopted projects in
various robotics domains, and organize an open source hardware
development process with best practices and strategies
derived from the surveyed projects.
Few previous reviews of open source hardware have been
conducted, and to the authors' knowledge, none has taken an allencompassing
look at hardware across the various fields within
robotics. Reviews have looked at open source projects in specific
fields of robotics, such as the design of medical devices [11],
unmanned aerial vehicles (UAVs) [12], hardware in research
labs [13], and in educational applications [14], [15]. Initiatives
such as the ORH website [16] and the Open Source Hardware
Association's (OSHWA's) directory host a compilation of open
source mechanical and electrical hardware [17]. In addition to
its directory of projects, OSHWA also promotes open source
hardware use to general audiences, establishes shared principles
of the open source hardware movement, and certifies projects
that meet its standard of open source compliance. More recently,
academic journals dedicated to open source design in science
[18], [19], [20] and special issues [21] have recognized the
impact of open source hardware specifically in robotics.
TABLE 1. The characteristics of ORH.
USER
Advantages
* easy to use, modify, and repurpose
* lower cost to acquire and service
* easy to repair and maintain
* upgradable on site and in the future
* access to the user community for large projects.
Challenges
* requires appropriate tools, equipment, and skills
* requires time and labor for replication
* lacks guaranteed, long-term support
* lacks comprehensive documentation
* lacks guaranteed reliability or robustness
The remainder of this article is organized as follows. The
" ORH " section focuses on what constitutes ORH as well as
on the characteristics of such hardware, noting the advantages
and challenges it brings to both users and developers,
along with best practices for developers to create effective
ORH projects. The " Survey of ORH Projects " section
presents a survey of more than 80 major ORH projects categorized
by the robotics subfield they are applied within.
Finally, the " Developing an ORH Project " section describes
the different stages in the process of developing new ORH
projects, highlighting the strategies adopted by successful
ORH projects. The characteristics, best practices, and surveys
from this article will also be made available through the
ORH website [16].
WHAT IS OPEN ROBOT HARDWARE
In this work, we review projects that can be ascribed as ORH,
which we define as satisfying the following inclusion criteria:
■ Open source: The design and auxiliary part files required
for redesign, fabrication, and assembly are made public,
along with the documentation that facilitates replication of
the work. The work should be disseminated with a license
that allows use, replication, modification, and sharing of
the various project components under the license's terms
and conditions.
■ Robotics oriented: The project has applications in a robotics
domain, either as a complete robot system or constituent
of a robot system.
■ Mechanical hardware oriented: The project focuses on
physical items with tangible mechanical components, such
as structural framework, mechanisms, actuators, and sensors.
The projects with supplementary electronics or software
elements that support the hardware are included, but
projects with solely electronics or software elements are
excluded from the scope of this review.
We also define the user of an ORH in the context of this
review as an entity replicating, using, modifying, or even
simply drawing inspiration from an ORH project. The user
is then at the receiving end of the content output by the
ORH's developer, defined here as the designer, distributor,
author, or any entity involved in the development, design,
documentation, or dissemination of the project. It is possible
DEVELOPER
* decentralized co-development and covalidation
* gains valuable and quick user feedback
* new applications of technology explored
* engages a large user community
* exposure by delivering impact to community.
* prepares comprehensive documentation
* guarantees design and fabrication simplicity
* keeps cost low for affordability
* selects license and dissemination strategy
* nurtures the engaged user community
* captures value from hardware
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