IEEE Robotics & Automation Magazine - March 2017 - 91
can be exploited to incorporate extra functionality in the
geometry of a part.
Among digital fabrication technologies, we focus on laser
cutting and low-end FDM 3-D printing (i.e., RepRap [32]
and derivatives), as these two technologies are commonly
available through FabLabs or online services. These two tech-
niques are complementary: 3-D printers are well suited for
producing small, complex 3-D parts, whereas laser cutters are
fast and work well to produce larger, stronger parts. However,
laser cutting is limited to flat parts. In our designs, the majori-
ty of custom parts are produced using laser cutting (> 90% by
part count), supplemented with 3-D-printed parts for com-
plex mechanisms and structures. By taking advantage of digi-
tal manufacturing techniques, we can incorporate extra
functionality in our custom parts. This can lead to a reduced
part count, simpler assembly, improved cable management,
and the like. Table 1 shows an overview of the connections
made possible through clever manipulation of the custom-
component geometry.
Wherever possible, assembly information is embedded
into the part geometry. Multiple methods can be used for this.
To begin with, all laser-cut and 3-D-printed parts are fitted
with engraved annotations, indicating part numbers and ori-
entation. This is useful to distinguish similar parts and helps
when referring to a part in written documentation. Many
parts are purposely made asymmetric, so they can be assem-
bled in only one way. Figure 4 shows how asymmetry can be
used to enforce correct orientation.
Laser-cut parts are made from ABS sheet material, with
one textured and one smooth side. Though not a deliberate
choice, the texture makes it very easy to distinguish between
mirror parts. This is especially useful because laser-cut parts
always have at least one plane of symmetry, parallel to the
plastic sheet. Laser-cut parts of the same subassembly are also
left connected to each other via small bridges, similar to a
sprue tree of a model kit. Of course, the embedded informa-
tion is not sufficient to completely document the assembly
process. The main documentation is provided through a wiki,
including photos, written instructions, and 3-D models.
Experiments and Platform Dissemination
Creating successful open-source hardware necessitates more
than merely making CAD files available. To stimulate wider
acceptance and adaptation, it is crucial to design with repli-
cation by others in mind . To stimulate this process, we orga-
nized a series of experiments in the form of workshops. The
workshops served a dual purpose: to test the design and
assembly processes of the toolkit and to kick-start a commu-
nity by attracting potential users to the workshops. In our
experiments, we investigated the assembly of standard Ono
robots and the design of novel social robots using our toolkit.
Details of the four experiments are summarized in Table 2.
The two assembly experiments involved participants who
had little or no experience in constructing physical objects.
Still, in both cases, participants were successful and assembled
working robots in the allotted time. Follow-up interviews
revealed that in both workshops, participants noted that they
liked how the workshop taught them a variety of practical
skills, such as soldering, in a short time and applied to a realis-
tic project. During the workshops, we provided participants
with assembly instruction handouts. However, we found that
the most effective technique to teach the assembly process
was to allow participants to recreate the robot based on the
example. The modular design also proved advantageous: it
stimulated parallelization, because participants could organize
themselves into groups focused on building one specific sub-
assembly. Naturally, there were limits to this method: eventu-
ally subassemblies needed to be joined together, at which
point the groups were forced to converge.
In experiments 3 and 4, participants used the Opsoro mod-
ules to prototype new social robot designs. Both experiments
had the same objective: to come up with an application for a
social robot, to design a character around that task, and finally
to create a working robot using the toolkit. However, there was
a large difference in the time scale: one day versus three
months. Consequently, experiment 3 used quick-and-dirty
prototyping techniques based on craft materials, whereas in
experiment 4, students had the time and infrastructure to cre-
ate high-fidelity prototypes. The results of the semester-long
experiment are shown in Figure 5. In both experiments, we
saw that participants tried to build basic actuated limbs,
though the hobby servos proved insufficient for this task,
revealing a weakness in the current toolkit.
Figure 4. Using asymmetry to improve the assembly process.
March 2017
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IEEE ROBOTICS & AUTOMATION MAGAZINE
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