IEEE Robotics & Automation Magazine - March 2017 - 90

Design Strategies
Ono and the Opsoro platform have gone through multiple
design iterations, from which we gained different insights
into the successes and failures of nonexperts who design
and build robots. The maker- and hacker-centric approach
lends itself well to quick design iterations because of the
use of digital manufacturing techniques. A summary of
this approach is given in this section. In our designs, we
1) use standardized components wherever appropriate
and 2) manufacture all custom components using digital
fabrication techniques. These two constraints serve to
improve the reproducibility of the designs. We rely on
digital manufacturing to produce components for our
designs. Other solutions are to create designs that can

be made using hand tools or designs that use only off-
the-shelf components.
The first point is self-evident: using standard components
is often cheaper and faster than creating a custom part for
the same purpose. The second point deserves some elabora-
tion. In the case of digital fabrication techniques, the infor-
mation required to produce a part is contained within a
digital file. Computer-controlled machines use these data to
produce physical parts, requiring little skill or craftsmanship.
This facilitates online sharing, lowers the barrier to copying,
and offers a high degree of repeatability. Another intrinsic
property of digital fabrication is that design complexity is
nearly free: printing a complex object takes the same time as
printing a simple object of the same volume. This property

Table 1. The 3-D-printed and laser-cut connections in the Opsoro system.
Figure

IEEE ROBOTICS & AUTOMATION MAGAZINE

Name

Notes

Snap connector
(ABS-ABS)

A reversible cantilever snap is used extensively to make 90° T-shaped
connections between two laser-cut parts. Used for connecting the different parts of the frame and for connecting modules to the frame.

Textile snap
(ABS-textile)

A variant on the snap connection is used to attach the outer textile to
the modules. A small laser-cut receiving part is sewn directly to the
textile. This receiving part mates with its counterpart in the modules.

Stitch pattern
(Foam-foam)

Ono's foam padding layer is made of flat, laser-cut foam parts that
are sewn together to form a 3-D shell. This 2-D pattern is generated
by flattening the 3-D shape in software. The border of the foam parts
is punctured by the laser at 1-cm intervals, facilitating the manual
sewing process.

Zip-tie anchor
(ABS-cable)

A feature to attach wiring to the frame using a zip tie. Previously,
two parallel slots were used, but this proved troublesome, as zip ties
needed to be inserted before assembly. Because of the dog-bone
shape, zip ties can be attached postassembly.

Nut trap
(3-D print-fastener)

Hexagonal pockets are used in 3-D-printed parts to connect to fasteners. A hex nut is pressed into the pocket, after which something else
can be attached to the printed part using a screw. This method is
much more reliable than cutting threads directly into the printed part.
The technique is also used extensively in 3-D-printed parts of the
RepRap project.

Servo spline
(ABS-servo)

Hobby servos use a splined output shaft with triangular teeth to
transfer torque to the output lever. While the dimensions of servos
are standardized, those of the horns that come with servos are not.
We solve this by cutting a radial pattern of lines in the circumference
of a circular hole. This melts the plastic in such a way that the hole
mates with the triangular teeth of the spline. Cutting the triangular
teeth directly does not work, as the geometry is too small.

March 2017

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