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\begin_layout Title
A New Open Source 3D-printable Mobile Robotic Platform for Education
\end_layout

\begin_layout Author
J.
 Gonzalez-Gomez, A.
 Valero, A.
 Prieto-Moreno, M.
 Abderrahim
\end_layout

\begin_layout Institute
J.
 Gonzalez-Gomez, A.
 Valero, M.
 Abderrahim 
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status open

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at
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 Robotics Lab.
 Universidad Carlos III de Madrid, Spain,
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status open

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email{{jggomez,avgomez,mohamed}@ing.uc3m.es}
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and
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 A.
 Prieto-Moreno 
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at
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 Universidad Autonoma de Madrid, Spain, 
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email{aprieto@uam.es}
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\begin_layout Abstract
In this paper we present the Miniskybot, our new mobile robot aimed for
 educational purposes.
 It has three new important features: 3D-printable on low cost reprap-like
 machines, fully open source (including mechanics and electronics) and,
 designed exclusively with open source tools.
 The presented robotic platform allows the students not only to learn robot
 programming, but also to modify easily the chassis and create new custom
 parts.
 Being open source involves that the robot can be freely modified, copied,
 and shared across the Internet.
 In addition, it is extremely cheap, being the cost almost exclusively determine
d by the servos, electronics and sensors.
\end_layout

\begin_layout Section
Introduction
\end_layout

\begin_layout Standard
Mobile robotics is increasingly entering the curriculum of many technical
 careers.
 Robotics is gaining terrain in industry and consequently more firms are
 enrolling candidates with experience in robot programming.
 For this reason, many universities are teaching robotics in their master
 and grade programmes
\begin_inset CommandInset citation
LatexCommand cite
key "Verner:1999, Rawat:2004"

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.
\end_layout

\begin_layout Standard
A common approach when teaching robot programming is the use of simulations,
 in which you can create different robot configurations with low effort.
 These ad-hoc robots can be also shared with other people, multiplying the
 number of 
\shape italic
out-of-shell
\shape default
 platforms 
\begin_inset CommandInset citation
LatexCommand cite
key "Carpin:Usarsim, Player:Stage"

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.
 Furthermore, the cost is zero, you may have as many robots as you want,
 and they will never break.
 But this solution has one drawback: simulated robots are not like real
 robots.
 Things working on simulation may not work the same on a real platform.
 In addition, students will never enjoy the same testing their ideas in
 a real robot than in a simulated one.
\end_layout

\begin_layout Standard
\begin_inset Float figure
wide false
sideways false
status open

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\align center
\begin_inset Graphics
	filename eps/Miniskybot-hand.eps
	scale 60

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\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
Left: The new Miniskybot v1.0 robot.
 Right: The educational skybot robot
\begin_inset CommandInset label
LatexCommand label
name "fig:Miniskybot-skybot"

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\end_inset


\end_layout

\end_inset


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\begin_layout Standard
Should it not be great that robots could be shared in the same way that
 code is shared (like in simulation)? If this could be possible researchers,
 professors and students could share their open source robots through the
 internet, exchange ideas with other research groups, compare prototypes,
 test their algorithms on different configurations, evolve others proposals...,
 such an idea is now possible and very affordable thanks to the open source
 Reprap-like 3D printers
\begin_inset CommandInset citation
LatexCommand cite
key "erik:print3d"

\end_inset

.
\end_layout

\begin_layout Standard
This opens a new way of teaching robotics with the following advantages:
\end_layout

\begin_layout Itemize
Fast prototyping of robotic platforms.
 
\end_layout

\begin_layout Itemize
Low cost printing of robot parts.
 
\end_layout

\begin_layout Itemize
Easy reconfiguration and adaptation of the platform (evolution).
 
\end_layout

\begin_layout Itemize
Easy sharing of robot models among people.
 
\end_layout

\begin_layout Itemize
Motivation for students not only to implement algorithms on an existing
 platform but also of platform designing and building.
 
\end_layout

\begin_layout Standard
In this paper, our new 3D printable Miniskybot robot platform is presented
 (shown in figure 
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Miniskybot-skybot"

\end_inset

).
 It is fully open source (both the mechanical and electronics parts) and
 exclusively designed with open source tools (Openscad, Freecad and Kicad).
 The parts were furtherer printed in a Makerbot Cupcake 3D printer.
\end_layout

\begin_layout Section
Motive and Problem Statement
\end_layout

\begin_layout Standard
Among the commercial educational platforms we can find a great variety of
 opportunities, starting with the well known Lego Robot, and going through
 the Meccano Robot, the RoboRobot robotic kit
\begin_inset Foot
status collapsed

\begin_layout Plain Layout
http://roborobo.koreasme.com/educational-robot-kit.html
\end_layout

\end_inset

, or the OWI Robot Arm Edge
\begin_inset Foot
status collapsed

\begin_layout Plain Layout
http://www.owiroboticarmedge.com/
\end_layout

\end_inset

.
 These products are quite extended in the educational environment, they
 are affordable, and easy to use.
 They usually come with associated software, which allows users to interface
 with the robot, having access to sensors and actuators, program them, and
 so forth.
 These platforms have being present for some years now in the educational
 environment.
 In 
\begin_inset CommandInset citation
LatexCommand cite
key "lund:robocup98"

\end_inset

 the authors demonstrated the idea of a children’s league for RoboCup, using
 robots constructed and programmed with the LEGO MindStorms kit to play
 soccer.
 Since then, RoboCupJunior has evolved into an international event where
 teams of young students build robots to compete in one of three challenges:
 soccer, rescue and dance 
\begin_inset CommandInset citation
LatexCommand cite
key "lund:robocup2000, Skar:robocup2002"

\end_inset

.
 In 
\begin_inset CommandInset citation
LatexCommand cite
key "Goldman:2004"

\end_inset

 is presented an educational robotics curriculum to enhance teaching of
 standard physics and math topics to middle and early high school students.
 This project was also centered around the Lego MindStorm.
\end_layout

\begin_layout Standard
The major disadvantage of these platforms is that they are close, and users
 can hardly adapt them to their necessities, instead, they must adapt to
 them.
 Even if in a industrial environment this may be the case, for research
 and education, the reconfiguration of the platform may be a great advantage
 in order to be able to deploy all the initiative of the researchers, professors
 or students.
 The Lego MindStorm inherits the "build-it-yourself" of the Lego traditional
 toys, but users are constrained to use the sensors provided by the manufacturer
, as well as the development software.
 Work could be done to hack this limitation, but this goes beyond the conception
 of the platform.
 A work trying to meet the "open source" and the "non-free" directions is
 done in 
\begin_inset CommandInset citation
LatexCommand cite
key "O'Hara:2003"

\end_inset

.
\end_layout

\begin_layout Standard
Ad-hoc mini-robots have been built by research groups or university spin-offs
 mainly for educational purposes.
 These solutions overcome the limitations of the commercial robots, providing
 cheaper and more adapted solutions.
 Examples are those of IntelliBrain-Bot 
\begin_inset Foot
status collapsed

\begin_layout Plain Layout
http://www.ridgesoft.com/intellibrainbot/intellibrainbot.htm
\end_layout

\end_inset

, Martin F.
 Schlogl's robots
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status collapsed

\begin_layout Plain Layout
http://www.mfs-online.at/robotics.htm
\end_layout

\end_inset

, the TankBot
\begin_inset Foot
status collapsed

\begin_layout Plain Layout
http://profmason.com/?p=320
\end_layout

\end_inset

, the Trikebot 
\begin_inset CommandInset citation
LatexCommand cite
key "Hsiut:trikebot"

\end_inset

, and many others.
 All these platforms derive from the trial to develop an effective and low-cost
 educational robot for education and home use, designed and built to fit
 the particular requirements of a teaching programme.
\end_layout

\begin_layout Standard
This had been also our way of teaching robotics during many years, with
 our Skybot
\begin_inset Foot
status collapsed

\begin_layout Plain Layout
http://goo.gl/MdRJs
\end_layout

\end_inset

 platform (shown in figure 
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Miniskybot-skybot"

\end_inset

).
 In our courses, the students build the Skybot from the scratch and then
 program it.
 Sometimes they are so motivated that they propose wonderful modifications
 to the robot design.
 Even though some modifications are known beforehand that will not work
 well, we would like the student to discover it by himself.
 But in any case, it is not possible to implement these modifications during
 the course.
 The cost (mainly in time) of building a new part made it unfeasible (think
 of sending the design to a manufacturer and waiting for the built part).
 At the end we had to keep the platform, or in the best case, change it
 for the following year (with new students).
\end_layout

\begin_layout Standard
Summarizing, the classical way of teaching robotics must focus, by necessity,
 on the programming of the robotic agent given a particular platform.
 Even if only this can be quite challenging and inspiring, with our current
 proposal of open, printable robots, the teaching programme must not be
 focused any more 
\shape italic
only
\shape default
 on the robotic agent, but it may also include its mechanical design.
 Beginning with a basic platform, like the Miniskybot, students can be guided
 through the design and programming process.
 In this way they may discover the high relation between hardware and software,
 and how each of them can, and must, adapt to the other requirements in
 order to achieve a precise task.
 They may learn that a particular mechanical design suits better a precise
 task, test different alternatives, and so forth.
 And something that is hardly considered in robotic programmes, students
 may learn that a change in the mechanical design could solve a problem
 better, faster, and more robustly that a software solution.
\end_layout

\begin_layout Section
On low-cost 3D Printers
\end_layout

\begin_layout Standard
Bradshaw et.
 al 
\begin_inset CommandInset citation
LatexCommand cite
key "bradshaw:3d"

\end_inset

 have recently made an study on low-cost 3d printing.
 They briefly run through the history of 3d printing, beginning in the late
 1970s.
 These more than thirty years have driven to 3d printers affordable for
 individuals
\begin_inset CommandInset citation
LatexCommand cite
key "Bowyer:3d"

\end_inset

, that allow them to print complicated engineering parts entirely automatically
 from design files that it is straightforward to share over the Internet.
 While open source software development has been studied extensively, relatively
 little is known about the viability of the same development model for a
 physical object’s design.
 3d printers are offering new possibilities of sharing physical objects.
 As they may defined using code, researchers can share their own parts,
 evolve them and "build" them straight forward using a 3D printer.
 This allows for a decentralized community to independently produce physical
 parts based on digital designs that are shared via the Internet.
 Apart from improving the device, dedicated infrastructure was developed
 by user innovators.
 As de Bruijn shows in his master thesis 
\begin_inset CommandInset citation
LatexCommand cite
key "erik:print3d"

\end_inset

, a hig incidence in modifications of hardware is present among people sharing
 parts and having access to 3d printers.
 This incidence is even greater than among those sharing software, and,
 the novelty is that hardware modifications are relatively easy for others
 to replicate.
 As it has been the case with software for many years, currently, there
 are also on-line repositories of parts, where people can download and upload
 their designs
\begin_inset Foot
status collapsed

\begin_layout Plain Layout
http://www.thingiverse.com
\end_layout

\end_inset


\end_layout

\begin_layout Section
The Miniskybot mobile robot platform
\end_layout

\begin_layout Standard
The new Miniskybot robotic platform is open source: all the mechanical and
 electronic design has been released with a copy-left license.
 What is more, it has been designed using only open source software tools.
 This is important because doing so it is guaranteed that anyone will be
 able to read, understand and modify the design files without license issues
 and using their preferred computer platform (Linux, Mac, BSD, Windows...).
\end_layout

\begin_layout Standard
\begin_inset Float figure
wide false
sideways false
status open

\begin_layout Plain Layout
\align center
\begin_inset Graphics
	filename eps/Miniskybot-minimal-parts.eps
	lyxscale 40
	scale 18

\end_inset


\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
Miniskybot.
 Minimal version
\begin_inset CommandInset label
LatexCommand label
name "fig:Miniskybot-Minimal-version"

\end_inset


\end_layout

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Standard
The Miniskybot is a differential drive robot composed of printable parts
 and two hacked hobby servos.
 It has been designed so that it can be printed on open source reprap-like
 3D-printer.
 Two mechanical designs have been developed.
 The first one is a minimal robot chassis shown in figure 
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Miniskybot-Minimal-version"

\end_inset

 (It is the 
\begin_inset Quotes eld
\end_inset

hello world
\begin_inset Quotes erd
\end_inset

 chassis).
 It consist of only four printable parts: the front, the rear and two wheels.
 They all are attached to the servos by means of M3 bolts and nuts.
 Standard O-rings are used as wheel's tires.
\end_layout

\begin_layout Standard
For making the robot stable, the rear part has two support legs that slide
 across the floor.
 Therefore this minimal robot chassis is only valid for moving on smooth
 flat surfaces.
\end_layout

\begin_layout Standard
The goal of this first design was to show the students a minimal fully working
 mobile robot for estimulating their minds.
 They were encouraged to improve this initial design.
\end_layout

\begin_layout Standard
\begin_inset Float figure
wide false
sideways false
status open

\begin_layout Plain Layout
\align center
\begin_inset Graphics
	filename eps/Miniskybot-parts.eps
	lyxscale 40
	scale 18

\end_inset


\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
Miniskybot Robot.
 Version 1.0
\begin_inset CommandInset label
LatexCommand label
name "fig:Miniskybot-Robot-v1.0"

\end_inset


\end_layout

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Standard
The version 1.0 chassis is an evolution of the previous design (figure 
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Miniskybot-Robot-v1.0"

\end_inset

).
 It consist of nine printable parts: the front, the rear, two wheels, the
 battery compartment, the battery holder and the castor wheel.
 An important feature is that the parts have been parameterized.
 Just changing some parameters new parts are obtained.
 For example the battery compartment is automatically changed if the parameter
 battery type is set from AAA to AA.
 In that case a new compartment capable of holding AA batteries (instead
 AAA) is generated.
 
\end_layout

\begin_layout Standard
The parametric feature is possible thanks to the open source Openscad
\begin_inset Foot
status collapsed

\begin_layout Plain Layout
http://openscad.org
\end_layout

\end_inset

 software used for designing the pieces.
 The parts themselves are not graphical meshes but scripts that determine
 how the pieces are built.
 When these scripts are 
\begin_inset Quotes eld
\end_inset

compiled
\begin_inset Quotes erd
\end_inset

 the graphical piece is generated and rendered on the screen, and later
 exported as an STL file for 3D printing.
\end_layout

\begin_layout Standard
This approach is very flexible.
 The parts are ASCII scripts that can be easily shared through internet,
 stored in repositories and so forth.
 Therefore the mechanical designs can be modified, used, and printed easily
 by different people around the world.
\end_layout

\begin_layout Standard
\begin_inset Float figure
wide false
sideways false
status open

\begin_layout Plain Layout
\align center
\begin_inset Graphics
	filename eps/miniskybot-skycube.eps
	scale 55

\end_inset


\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
Electronics.
 Skycube board
\begin_inset CommandInset label
LatexCommand label
name "fig:Electronics-Skycube-board"

\end_inset


\end_layout

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Standard
\begin_inset Float figure
wide false
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status collapsed

\begin_layout Plain Layout
\align center
\begin_inset Graphics
	filename eps/elecronic-diagram.eps
	scale 55

\end_inset


\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
Electronic diagram
\begin_inset CommandInset label
LatexCommand label
name "fig:Electronic-diagram"

\end_inset


\end_layout

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Standard
The electronic board is also a minimal design with only the necessary components
 for controlling the robot.
 It includes an 8-bit pic16f876a micro-controller, headers for connecting
 the servos, an I2C bus for the sensors, serial connection to the PC, a
 test led and a switch for turning on and off (figure 
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Electronics-Skycube-board"

\end_inset

).
\end_layout

\begin_layout Standard
An electric connection diagram is shown in figure 
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Electronic-diagram"

\end_inset

.
 The servos are connected directly to the board.
 The speed is set by means of two PWM signals.
 The two ultrasound sensors in the robot's front are connected thought the
 I2C bus.
 Robot version 1.0 have two ultrasound sensors, but as they are connected
 to the I2C bus, more sensors can be easily added.
 For the power supply four AAA type standard batteries are used.
 The board can be connected to the PC by a serial RS232 connection for downloadi
ng the firmware.
 The PCB has been designed with the open source Kicad tool
\end_layout

\begin_layout Standard
The robot is programed in C language using the open source SDCC cross compiler.
 The binary files are downloaded into the board by means of a serial cable.
 Previously a bootloader firmware needs to be burned in the flash memory
 by means of the ICSP connector.
 Loading the firmware this way the students do not need to use any programming
 hardware but just a simple cable.
 Also, the download process is done very fast.
 Only a few seconds are needed for completing it.
\end_layout

\begin_layout Standard
\begin_inset Float figure
wide false
sideways false
status open

\begin_layout Plain Layout
\align center
\begin_inset Graphics
	filename eps/Miniskybot-physical-parts.eps
	scale 59

\end_inset


\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
The MiniSkybot robot printed in red ABS
\begin_inset CommandInset label
LatexCommand label
name "fig:The-MiniSkybot-robot"

\end_inset


\end_layout

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Section
Results
\end_layout

\begin_layout Standard
The Miniskybot robot has been successfully printed on a Makerbot Cupcake
 3D printer in ABS plastic (Acrylonitrile Butadiene Styrene).
 The machine is equipped with the latest MK5 extruder and a heated build
 platform.
 It is very affordable.
 The printer's cost is 680€.
\end_layout

\begin_layout Standard
All the parts have been printed without raft.
 The software used was Replicator-G 0023 with Skeinforge 35.
 In figure 
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:The-MiniSkybot-robot"

\end_inset

 a red prototype is shown, along with all the parts needed for assembling
 the robot.
 
\end_layout

\begin_layout Standard
The total printing time is 2 hours and 50 minutes and the total robot cost
 is around 57€, as shown in table 
\begin_inset CommandInset ref
LatexCommand ref
reference "tab:Printing-time-cost"

\end_inset

.
 It can be seen that the cost of the chassis (the printable parts) is marginal:
 less than 1€.
 Therefore, the robot cost is determined by the electronics, motors and
 sensors, but not by the mechanics.
\end_layout

\begin_layout Standard
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--------
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----
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\series bold
Total:
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170 min (2h, 50min)
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56.6€
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</row>
</lyxtabular>

\end_inset


\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
Printing time and cost of the MiniSkybot v1.0 robot
\begin_inset CommandInset label
LatexCommand label
name "tab:Printing-time-cost"

\end_inset


\end_layout

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Standard
Although this kind of 3D printers are not meant for production but for prototypi
ng, they can be used for building small series of robots for giving courses
 on robotics to small groups.
 Given that every 3h the parts for a new robot are built and if the machine
 is working without interruption, 8 robot chassis per day can be printed.
 In figure 
\begin_inset CommandInset ref
LatexCommand ref
reference "fig:Miniskybot-group"

\end_inset

 a group of six Miniskybots is shown, printed in different colors.
\end_layout

\begin_layout Standard
\begin_inset Float figure
wide false
sideways false
status open

\begin_layout Plain Layout
\align center
\begin_inset Graphics
	filename eps/Miniskybot-group.eps
	scale 60

\end_inset


\end_layout

\begin_layout Plain Layout
\begin_inset Caption

\begin_layout Plain Layout
A group of six MiniSkybot robots (v1.0) in different colors
\begin_inset CommandInset label
LatexCommand label
name "fig:Miniskybot-group"

\end_inset


\end_layout

\end_inset


\end_layout

\end_inset


\end_layout

\begin_layout Section
Conclusion and future work
\end_layout

\begin_layout Standard
Using the latest open source 3D-printers a new printable robotic platform
 has been designed, built and tested.
 Our results confirm he viability of these new printable robots.
 They offer new important features for educational purposes.
 First, they are very flexible.
 The students can design new custom pieces easily which are printed and
 tested very fast.
 Therefore the robot can be mechanically evolved during the courses.
 Second, the robot can be deeply studied, modified, copied and distributed
 by anyone.
 This way the robot can evolute not only in our university but also around
 the world.
 This feature is enhanced by the fact that the mechanical parts are Openscad
 ASCII scripts, like any other software.
 Consequently, they behave like open source software and can be distributed
 and shared in a similar way.
 Finally, the total cost is very low, depending almost exclusively on the
 servos, electronics and sensors.
 The Miniskybot v1.0 costs 57€ and the printing time is around 3h, which
 means that eight robot chassis per day can be printed.
\end_layout

\begin_layout Standard
As a future work we are planning to continue evolving the robot in collaboration
 with our students, designing new parts for sensors, wheels, whegs and so
 on.
\end_layout

\begin_layout Section*
Acknoledgements
\end_layout

\begin_layout Standard
We would like to thank to Prof.
 Luis Moreno for his support.
 Also we would like to thank to all the students who have contributed to
 the evolution of the Miniskybot robot.
 Special thanks to Olalla bravo for the design of the printable castor wheel.
\end_layout

\begin_layout Standard
\begin_inset CommandInset bibtex
LatexCommand bibtex
bibfiles "bibtex"
options "plain"

\end_inset


\end_layout

\end_body
\end_document
