Proceedings of the Third International Conference on Tangible and Embedded Interaction (TEI'09), Feb 16-18 2009, Cambridge, UK
Plywood Punk:
A Holistic Approach to Designing Animated Artifacts
Peter Schmitt
MIT Media Laboratory
Smart Cities Group
E15-120f, 20 Ames Street
Cambridge, MA 02142
[email protected]
Susanne Seitinger
MIT Media Laboratory
Smart Cities Group
E15-120g, 20 Ames Street
Cambridge, MA 02142
[email protected]
cannot be influenced. Many rapid prototyping tools
propagate the same logic. For example, laser cutters are
more frequently used to build casings that hide embedded
electronics than mechanical components that celebrate
them. And even complex electronic devices such as mobile
phones, music-players and laptops sport smooth, uniform
surfaces that hide embedded technologies. How can we
approach the design of animated artifacts holistically to
recapture the magic of engaging with them?
ABSTRACT
Animated artifacts require many different electronic and
mechanical components as well as appropriate drive
software. This complexity has led to a kit-of-parts thinking
in designing robotic assemblies. For example, Dynamixel
or Lego Mindstorms provide designers, enthusiasts and
children standard components from which they can
assemble a multitude of creations. Despite the openendedness of these kits, the most basic component parts
such as servos present a designer with a set of constraints
such as form that she cannot control. The underlying logic
for these factors derives from mass-production rather than
specific design requirements. The resulting black box
becomes a factor around which design is created rather
than an integral part of the completed artifact. In this paper,
we explore the benefits of designing animated artifacts
holistically. As an example, we compare the re-design of a
servo in plywood and electronic components with a typical
RC servo. This juxtaposition demonstrates how formfactors, materials and materiality, tactile and visual
qualities and the performative aspects of a design can be
reintroduced into design thinking for animated artifacts.
From the example, we distill four guidelines for a design
approach: (1) iterate, (2) explore material properties, (3)
engage the performative aspects of the artifact, (4) cross
disciplinary boundaries.
In the first part of this paper, we describe re-designing a
servo unit in plywood (see Figure 1). The result is
compared with an off-the-shelf RC servo. In the second
part we review related work and describe an iterative and
interdisciplinary design approach to interactive and
animated artifacts for embedded computing applications.
Keywords
mechatronics, robotics, design, design methodology,
prototyping
INTRODUCTION
Devices such as Sony’s robotic dog Aibo or robotics kits
such as Lego Mindstorms [14] or Dynamixel [3] have
enabled more people to engage with animated devices.
However, these devices lack the intensity and material
diversity of traditionally crafted artifacts. Robotics kits
provide designers with a series of given constraints that
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Figure 1. Completed plywood servo. (All photographs by
authors unless otherwise noted.)
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Proceedings of the Third International Conference on Tangible and Embedded Interaction (TEI'09), Feb 16-18 2009, Cambridge, UK
BUILDING A PLYWOOD SERVO
Actuators enable designers to animate their artifacts and
expand the potential for exciting interactions with tangible
and embedded technologies. In most cases, designers
depend on off-the-shelf actuators to enable the motions
they envision. In the following example, we build a servo
unit in plywood to explore what is typically a black box in
the design process.
Attach a clock hand to the output shaft for visual
feedback on servo performance
Provide standard communication interfaces like serial,
USB, or TWI to drive the unit
Materials
Most of the structure and gears are constructed in plywood.
Some of the smaller gears are in Delrin, a plastic designed
for mechanical applications. The plywood and Delrin
components were designed in CAD software and cut out on
a laser cutter. Screws serve as axles for the gears. A small
electric motor, electronic components (microcontroller,
MOSFETs, resistors, capacitors and optical interrupter)
were embedded in a plywood “circuit” board (see Figure
5).
Conventional RC Servo unit
A standard radio-controlled (RC) servo unit (see Figure 2)
contains a DC motor, gearing, and control circuitry. Based
on coded input signals the motor positions an output shaft
to a particular angular position under varying conditions.
Exterior forces such as impacts or the artifact’s own weight
also impact the servo’s position. In order to maintain a
desired position, the coded signal must be continuously
adjusted. Applications for RC servo units include radio
controlled airplanes, cars and puppets as well as robotics
and other actuated devices.
Discussion
The plywood servo enables certain design explorations and
also engenders new challenges. On the one hand, the
tactile, auditory, and visual characteristics as well as the
accuracy of the plywood servo can be controlled by the
designer. On the other hand, the unit is much larger and
slower than a typical servo and the design-build process is
more time-consuming and complex.
Typically, a PWM signal is used to set the angular position
of the servo’s output shaft. A 1ms pulse causes the shaft to
turn to its zero position while a 2ms pulse results in the
maximum position. Motion ranges from 0deg to 90deg or
180deg. The PWM signal is refreshed 50 times per second.
When the pulse length changes very little the servo turns
slowly. When the pulse length changes very quickly the
servo turns at maximum velocity (approximately 200ms per
60deg).
The plywood servo celebrates the internal workings of the
unit. Much like skeleton watches (see Figure 3), the
plywood servo allows the user to peer into the mechanical
routines of the device. This visual connection can increase
the visceral relationship between user and artifact. In
addition, the plywood servo allows the designer to achieve
a desired gear ratio and thus specific levels of accuracy.
Internally, a feedback loop assures position accuracy. A
potentiometer connected to the output shaft is continuously
monitored. Its resistance provides feedback on the actual
position of the shaft. A PID control algorithm compares
actual position to signaled position. It adjusts speed and
force of the motor to reach a desired position. With a
constant input signal, the PID control algorithm will also
drive the motor to maintain the signaled position. [11, 16]
Figure 3. Skeleton watch. Original photograph by
readerwalker, Creative Commons License,
http://www.flickr.com/photos/readerwalker/2053060075/
Despite the customized gears, the plywood servo still relies
on certain off-the-shelf components (electric motor,
electronics). Selecting which black boxes to unpack
depends on a particular design question. In some cases, it
may be important to redesign a servo from scratch. In other
cases, it may be more appropriate to use finished
components.
Figure 2. Standard RC servo.
Plywood Servo
The components of a servo described above were distilled
into the following elemental steps (see also Figure 4):
Connect motor and gears to an output shaft
Sense motor rotations as a simple feedback loop
These tradeoffs are subject to design decisions that should
not be overlooked in the early stages of the process. From
an engineering point of view, the plywood servo is bigger,
slower and less powerful. From a design point of view, the
plywood servo provides more flexibility in terms of shape,
materials and use cases. It enables integrated designs with
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Proceedings of the Third International Conference on Tangible and Embedded Interaction (TEI'09), Feb 16-18 2009, Cambridge, UK
Design Principles
more seamless connections between mechanical and
electronic components.
Based on our experience with the plywood servo, we
propose four design principles for animated artifacts:
(1) iterate, (2) explore material properties, (3) engage the
performative aspects of the design, (4) cross disciplinary
boundaries.
DESIGN APPROACH
The conventional servo presents the designer with a black
box. The form factor and behaviors cannot be transformed
after the fact. The plywood servo unlocks a rich design
space to be explored and customized for specific
interaction cases. Based on the process described above,
we propose an iterative and interdisciplinary approach to
designing interactive and animated artifacts for embedded
computing applications.
Iterate on the Design
Homing in on a final design proposal can only be
accomplished
through
iteration.
Iteration
also
accommodates changing requirements throughout the
design process. [4,7] Figure 4 illustrates the steps of
building the plywood servo and the transformations the
initial design underwent.
Related Work
Servos are key components for designing animated
artifacts. Dynamixel [3] has developed servos that can be
daisy-chained together and addressed via a serial
communication protocol. They have also implemented
force sensors and rotary encoders to replace
potentiometers. However, Dynamixel is still a proprietary
kit and compatibility is limited to their products.
OpenServo [9] is a project particularly focused on making
servo software and hardware more accessible. The
project’s most significant contribution consists in
simplifying communications with most types of RC servos.
A PCB board was developed that can be placed into most
RC servo unit casings. This PCB board makes it possible to
communicate directly with the servo via serial or USB
protocols. Ease of communication significantly broadens
the appeal of servos for new applications.
The mechatronic plywood design is inspired by several
fields: tangible user interfaces, construction kits for
designing embedded and tangible artifacts, and modular
user interface design approaches. Tangible user interfaces
enable users to intuitively interact with everyday artifacts
rather than with WIMP (windows, icon, menu, pointing
device) tools. This work has increased people’s awareness
for the look and feel of computational artifacts, including
animated artifacts. [5,6] Topobo, for example, is a tangible
user interface that enables children to explore kinetics. [12]
Zuckerman’s flow blocks are plywood blocks with simple
feedback elements for exploring systems design. [17]
Figure 4. Design iterations for plywood servo
Explore Material Properties
A conventional servo is primarily composed of plastic and
metal parts hidden behind a casing. In the example
described above, these same parts are mostly constructed
from plywood and integrated with electronics (see Figure
5). While plywood would typically not be the material of
choice for mechanical components the plywood servo
presents a more engaging tactile, auditory, and visual
experience for the user that may be more important design
requirements for a specific problem.
Construction kits for children such as LEGO Mindstorms
enable them to design many types of animated artifacts.
The latest version of this construction kit is called
PICOCricket and can be used alongside typical craft
materials. Modular input and output components as well as
extendible wires make it easy for children to build their
own animated artifacts with materials of their choosing.
[10,14] The Arduino and Lilypad Arduino platforms
provide similar flexibility for prototyping and design
activities. [1,2]
Finally, there has been a large body of work also related to
tangible user interfaces in the domain of flexible user
interface design, for example Villar’s malleable interface
approach. [15]
Figure 5. Integrated electronics
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Proceedings of the Third International Conference on Tangible and Embedded Interaction (TEI'09), Feb 16-18 2009, Cambridge, UK
Engage the Performative Aspects of the Artifact
2. Buechley, L., Eisenberg, M., Catchen, J., and Crockett,
A. The LilyPad Arduino: Using computational textiles
to investigate engagement, aesthetics, and diversity in
computer science education. In Proc. of CHI 2008,
ACM Press (2008), 423-432.
Rather than relying on off-the-shelf components designers
should open black boxes instead of encasing them in
plastic. Opening the black box unlocks the hidden
mechanical and electronic components that are embedded
within the device. This approach allows us to experience
the performative aspects of an artifact just like the turning
gears of a skeleton watch or a beautiful cloth [2].
3. Dynamixel. Available at
http://www.robotis.com/zbxe/main
4. Hartmann, B., Klemmer, S. R., Bernstein, M., Abdulla,
L., Burr, B., Robinson-Mosher, A., and Gee, J. 2006.
Reflective physical prototyping through integrated
design, test, and analysis. In Proc. of UIST, ACM Press
(2006), 299-308.
Rebuilding the most elemental components can also lead to
exciting new directions for an overall concept. In
education, constructionism proposes that children will learn
more about science and engineering by designing and
building their own experiments and experimental devices
[13]. Designers can gain the same beneficial insights about
their artifacts by constructing them from the ground up.
5. Ishii, H. Tangible pixels: Beyond pixels. In Proc. of TEI
2008, ACM Press (2008), XV-XXV.
6. Ishii, H. and Ullmer, B. Tangible bits: Towards
seamless interfaces between people, bits and atoms. In
Proc. of CHI 1997, ACM Press (1997), 234-241.
Cross Disciplinary Boundaries
Designing animated artifacts requires knowledge from
many fields including mechanical, electrical, and control
systems engineering as well as interaction and industrial
design. Throughout the design process it is essential to
cross disciplinary boundaries. First, experts from multiple
disciplines should weigh in. Second, experts should not be
restricted to their particular discipline. Rebuilding a servo
from the ground up would be trivial for a mechanical
engineer and akin to reinventing the wheel. However, this
exercise may be the only route to breaking out of
preconceived ideas about how this component should be
constructed. [8] This process will result in artifacts that
address broader scientific, design and educational
communities.
7. Laurel, B. ed. Design Research: Methods
Perspectives. Cambridge, MA: MIT Press, 2003.
and
8. Mackay, W.E. From Gaia to HCI: On multidisciplinary
design and coadaptation. In Erickson, T., McDonald
D.W., eds. HCI Remixed. Cambridge, MA: MIT Press,
2008.
9. OpenServo Community-based Project. Available at
http://www.openservo.com/
10.PICO Cricket. Available at http://www.picocricket.com/
11.PID Controller. Available at
http://en.wikipedia.org/wiki/PID_controller
CONCLUSIONS AND REFLECTIONS
12.Raffle, H. S., Parkes, A. J., and Ishii, H. Topobo: a
constructive assembly system with kinetic memory. In
Proc. of CHI, ACM Press (2004), 647-654.
Industrial designers approach the design of artifacts from
scratch. They are not expected to create new objects from a
kit of parts. Designing animated artifacts should be equally
unconstrained and designers should feel comfortable
moving across disciplinary boundaries. While the number
of open source hardware platforms is increasing, many of
the components necessary for building animated artifacts
remain black boxed. In addition, these approaches should
be transferred from prototyping environments to product
design and development. Future work includes developing
more complex assemblies of plywood mechatronics for
specific animated artifacts and testing them with users.
13.Resnick, M., Berg, R., and Eisenberg, M. Beyond black
boxes: Bringing transparency and aesthetics back to
scientific investigation. In Journal of the Learning
Sciences 9, 1 (2000), 7-30.
14.Rusk, N., Resnick, M., Berg, R., and Pezalla-Granlund,
M. New pathways into robotics: Strategies for
broadening participation. Journal of Science Education
and Technology 17, 1 (2008), 59-69.
15.Villar, N. and Gellersen, H. A malleable control
structure for softwired user interfaces. In Proc. of TEI
2007, ACM Press (2007), 49-56.
ACKNOWLEDGMENTS
We would like to thank the anonymous reviewers for their
constructive comments. We are grateful to Prof. William J.
Mitchell and the MIT Media Laboratory sponsor consortia
for supporting this research.
16.Wescott, T. PID without a PhD. In Embedded Systems
Programming.
Available
at:
http://www.embedded.com/2000/0010/0010feat3.htm
REFERENCES
17.Zuckerman, O., Arida, S., and Resnick, M. Extending
tangible interfaces for education: Digital montessoriinspired manipulatives. In Proc. of CHI 2005, ACM
Press (2005), 859-868.
1. Arduino physical computing platform. Available at
http://www.arduino.cc/
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