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\begin{document}

\title{A New Open Source 3D-printable Mobile Robotic Platform for Education}


\author{J. Gonzalez-Gomez, A. Valero-Gomez, A. Prieto-Moreno, M. Abderrahim}


\institute{J. Gonzalez-Gomez, A. Valero-Gomez, M. Abderrahim \at Robotics Lab,
Carlos III University of Madrid, Spain,\\
 \email{{jggomez,avgomez,mohamed}@ing.uc3m.es} \\
\and A. Prieto-Moreno \at Autonomous University of Madrid, Spain,
\email{aprieto@uam.es}}

\maketitle
\abstract{In this paper we present the Miniskybot, our new mobile robot aimed for educational purposes, and the underlying philosophy. 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 the robot can be freely modified, copied, and shared across the Internet. In addition, it is extremely cheap, being the cost almost exclusively determined by the cost of the servos, electronics and sensors.}


\section{Introduction}

Mobile robotics is increasingly entering the curricula of many technical
studies. Robotics is gaining terrain in industry and consequently
more firms are recruiting candidates with experience in robot programming.
For this reason, many universities are teaching robotics in their
master and degrees programmes\cite{Verner:1999,Rawat:2004}.

A common approach when teaching robot programming is the use of simulations,
in which the user can create different robot configurations with low
effort. These ad-hoc robots can be also shared with other people,
multiplying the number of \textit{out-of-shell} platforms \cite{Carpin:Usarsim,Player:Stage}.
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
not enjoy the same testing their ideas on a real robot than on a simulated
one.

%
\begin{figure}
\begin{centering}
\includegraphics[scale=0.6]{eps/Miniskybot-hand}
\par\end{centering}

\caption{Left: The new Miniskybot v1.0 robot. Right: The educational skybot
robot\label{fig:Miniskybot-skybot}}

\end{figure}


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 proposals from others..., such an idea is now possible and
affordable thanks to the open source Reprap-like 3D printers\cite{erik:print3d}.

This opens a new way of teaching robotics with the following advantages:
\begin{itemize}
\item Fast prototyping of robotic platforms. 
\item Low cost printing of robot parts. 
\item Easy reconfiguration and adaptation of the platform (evolution). 
\item Easy sharing of robot models among people. 
\item Motivation for students not only to implement algorithms on an existing
platform but also to design and build new platforms. 
\end{itemize}
In this paper, our new 3D printable Miniskybot robot platform is presented
(shown in figure \ref{fig:Miniskybot-skybot}). 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.


\section{Motive and Problem Statement}

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%
\footnote{http://roborobo.koreasme.com/educational-robot-kit.html%
}, or the OWI Robot Arm Edge%
\footnote{http://www.owiroboticarmedge.com/%
}. 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 been present for some years now in the educational environment.
In \cite{lund:robocup98} the authors demonstrated the idea of a children\textquoteright{}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 \cite{lund:robocup2000,Skar:robocup2002}. Goldmand et al.\cite{Goldman:2004}
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.

The major disadvantage of these platforms is that they are close.
The users can hardly adapt them to their necessities, and instead,
they must adapt to them. 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 \textquotedbl{}build-it-yourself\textquotedbl{} of the Lego traditional
toys, but users are constrained to use the sensors provided by the
manufacturer, as well as the development software. An effort could
be done to work around this limitation, but this goes beyond the original
design of the platform. A work trying to meet the \textquotedbl{}open
source\textquotedbl{} and the \textquotedbl{}non-free\textquotedbl{}
directions is done by O'Hara et al\cite{O'Hara:2003}.

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. Efforts have been done with the intention of developing
effective and low-cost robots for education and home use, designed
and built to fit the particular requirements of a teaching programme.
Examples are those of IntelliBrain-Bot %
\footnote{http://www.ridgesoft.com/intellibrainbot/intellibrainbot.htm%
}, Martin F. Schlogl's robots%
\footnote{http://www.mfs-online.at/robotics.htm%
}, the TankBot%
\footnote{http://profmason.com/?p=320%
}, the Trikebot \cite{Hsiut:trikebot} among many others. 

This had been also our way of teaching robotics during many years,
with our Skybot%
\footnote{http://goo.gl/MdRJs%
} platform (shown in figure \ref{fig:Miniskybot-skybot}). In our courses,
the students build the Skybot from 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 due to the time it takes to the manufacturer
to build the parts. At the end we had to keep the platform, or in
the best case, change it for the next course with new students.

To summarize, 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 source printable robots, the teaching
programme must not be focused any more \textit{only} 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 tight 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 than a software solution.


\section{On low-cost 3D Printers}

Bradshaw et. al \cite{bradshaw:3d} have recently made a 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 affordable 3D printers for individuals\cite{Bowyer:3d}, and allow
them to print complex 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 design. 3D printers are offering new possibilities
of sharing physical objects. As they can be defined using code, researchers
can share their own parts, evolve them and \textquotedbl{}build\textquotedbl{}
them straight forward using 3D printers. 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 infrastructures were developed by user innovators.
As Bruijn shows in his master thesis \cite{erik:print3d}, a considerable
improvement of hardware are proposed by people sharing parts and having
access to 3D printers. This 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%
\footnote{http://www.thingiverse.com%
}.

%
\begin{figure}
\begin{centering}
\includegraphics[scale=0.6]{eps/3D-printers-1}
\par\end{centering}

\caption{Pictures of some open source 3D printers. From left to the right:
RepRap Darwin, the first generation (May, 2007); Reprap Mendel (Sep,
2009) the second generation; Makerbot Cupcake (April, 2009), the first
commercial open-source 3D printer; Makerbot Thing-o-Matic (Sep, 2010),
second version\label{fig:3D-printers-history}}

\end{figure}


In figure \ref{fig:3D-printers-history} four of the most important
open source 3D-printers are shown. The origin of these kind of printers
was the reprap project%
\footnote{http://reprap.org/wiki/Main\_Page%
} \cite{Jones2011} started by Adrian Bowyer in 2004. The aim of this
project was to develop an open-source self-replicating machine. In
May 2007 the first prototype, called Darwin was finished and some
days later, in May 29th the first replication was achieved. Since
then, the reprap community (original reprap machines and derived designs)
has been growing exponentially\cite{erik:print3d}. The current estimated
population is around 4500 machines. The second reprap generation,
called Mendel, was finished in September 2009. Some of the main advantages
of the Mendel printers over Darwin are bigger print area, better axis
efficiency, simpler assembly, cheaper, lighter and more portable. 

Initially, both Darwin and Mendel were not designed for the general
public but for people with some technical background. As the reprap
project was open-source, small companies were created to start shelling
these 3D printers, as well as derived designs. The first company was
Makerbot Industries%
\footnote{http://www.makerbot.com/%
}, who shipped a first batch of their Cupcake CNC in April 2009. By
the end of 2009 they had shipped nearly 500 complete kits. After operating
for a year they had sold about 1000 kits in April 2010. Their latest
design is the thing-o-matic printer, announced in September 2010.
It is really easy to build and use, and their cost is around 950¤.

%
\begin{figure}
\begin{centering}
\includegraphics[scale=0.7]{eps/MADRE-clone-wars}
\par\end{centering}

\caption{Our open source 3D printers at Carlos III University of Madrid. On
the left: the Makerbot Thing-o-matic, called MADRE. On the right:
a Prusa Mendel prototype, being built by the students\label{fig:Carlos-III-3D-printers}}



\end{figure}


Currently, at the System Engineering and Automatic Department of Carlos
III University of Madrid we have one thing-o-matic available for the
students, shown in figure \ref{fig:Carlos-III-3D-printers}. It was
fully assembled by the students. Anyone has free access to it so that
they can print whatever designs they want. Our main goal is to stimulate
their imagination and enhance their creativity. 

In addition we have started a project, called {}``Clone wars''%
\footnote{http://asrob.uc3m.es/index.php/Proyecto:\_Clone\_wars%
}, in which a group of students are building their own reprap printers
from the scratch. All the parts are being printed in our thing-o-matic,
which has been named MADRE (that means mother in spanish). We have
chosen the Prusa Mendel model as the design to build, because it is
very well documented and it is rather easy to assemble. In figure
\ref{fig:Carlos-III-3D-printers}(on the right) the first prototype
is shown. In total the students are building 20 of them.


\section{The Miniskybot mobile robot platform}


\subsection{Introduction}

The new Miniskybot robotic platform%
\footnote{http://www.thingiverse.com/thing:7989%
} is open source: all the mechanical and electronic design has been
released with a copy-left license. Furthermore, only open source software
tools have been employed. This is important because in 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...).

The Miniskybot is a differential drive robot composed of printable
parts and two modified (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 minimal version and the
1.0.


\subsection{Minimal version}

%
\begin{figure}
\begin{centering}
\includegraphics[scale=0.18]{eps/Miniskybot-minimal-parts}
\par\end{centering}

\caption{Miniskybot. Minimal version\label{fig:Miniskybot-Minimal-version}}

\end{figure}


The first prototype developed was a minimal robot chassis. The idea
was to design a printable robot with the minimal parts, a kind of
{}``hello world'' robot. It is shown in figure \ref{fig:Miniskybot-Minimal-version}.
It consist of only four printable parts: the front, the rear and two
wheels. They are all attached to the servos by means of M3 bolts and
nuts. Standard O-rings are used as wheel tires. For making the robot
stable, the rear part has two support legs that slide across the floor.
Therefore this prototype is only valid for moving on smooth flat surfaces.
The goal of this first design was to show the students a minimal fully
working mobile robot for stimulating their minds. They were encouraged
to improve this initial design.


\subsection{Miniskybot 1.0}

%
\begin{figure}
\begin{centering}
\includegraphics[scale=0.18]{eps/Miniskybot-parts}
\par\end{centering}

\caption{Miniskybot Robot. Version 1.0\label{fig:Miniskybot-Robot-v1.0}}

\end{figure}


The version 1.0 chassis is an evolution of the previous design (figure
\ref{fig:Miniskybot-Robot-v1.0}). 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 this case
a new compartment capable of holding AA batteries (instead AAA) is
generated. 

The parametric feature is possible thanks to the open source Openscad%
\footnote{http://openscad.org%
} software used for designing the pieces. The parts themselves are
not graphical meshes but scripts that determine how they are built
by primitive geometric forms. When these scripts are {}``compiled''
the graphical part is generated and rendered on the screen, and later
exported as an STL file for 3D printing.

This approach is very flexible because 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.


\subsection{Electronics and sensors}

%
\begin{figure}
\begin{centering}
\includegraphics[scale=0.55]{eps/miniskybot-skycube}
\par\end{centering}

\caption{Electronics. Skycube board\label{fig:Electronics-Skycube-board}}

\end{figure}


%
\begin{figure}
\begin{centering}
\includegraphics[scale=0.55]{eps/elecronic-diagram}
\par\end{centering}

\caption{Electronic diagram\label{fig:Electronic-diagram}}

\end{figure}


The Miniskybot's electronics is the Skycube board%
\footnote{http://www.iearobotics.com/wiki/index.php?title=Skycube%
}. It was previously designed for fitting into the Y1 modules for controlling
the modular robots used for research purposes\cite{Gonzalez-Gomez2008}.
It is 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 powering the circuit (figure
\ref{fig:Electronics-Skycube-board}).

An electric connection diagram is shown in figure \ref{fig:Electronic-diagram},
where 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 downloading the firmware. The
PCB has been designed with the open source Kicad tool

The robot is programed in C language using the open source SDCC cross
compiler and 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 is done very fast, where
it takes only a few seconds to complete the whole process. 


\section{Derived designs from Miniskybot}

In contrast to our previous Skybot robot which remained unmodified
for many years, the MiniSkybot has inspired the imagination of the
students which have developed new designs in record time. There were
two main reason for this motivation, according to the students: 1)
Full access to the Miniskybot {}``source code'', 2) Being able to
turn their thoughts on real physical objects very fast, thanks to
the 3D printer. The former let the students to fully understand a
real robot and realize that it is not so difficult to design the mechanical
parts. Instead of starting from the scratch, they just simply start
modifying the Miniskybot parts. The latter is related to the strong
feeling of happiness and power that the students have when they see
their designs become a reality. 

In the following sections two new derived design are presented, fully
created by second year undergraduate engineering students with no
special knowledge on mechanics.


\subsection{Caterpillator}

%
\begin{figure}
\begin{centering}
\includegraphics[scale=0.7]{eps/orugator}
\par\end{centering}

\caption{The caterpillator robot\label{fig:The-caterpillar-robot}}



\end{figure}


The Miniskybot robot uses two drive wheels for moving. Two students
wonder if it was possible to design a robot with tracks instead of
wheels. Inspired by this chain an pinions design in thingiverse%
\footnote{http://www.thingiverse.com/thing:5656%
}, Olalla Bravo and Daniel Gomez decided to create the first printable
track for mobile robots. After some initial failed tries, they succeed
in building a parametric track%
\footnote{http://www.thingiverse.com/thing:7209%
}. The beauty of this design was not only its functionality but its
property of being parametric. Just changing some parameters, different
tracks can be obtained, as well as the necessary pinions. In addition,
3mm plastic spool was used as pins for the links. Therefore no special
screws and nuts were necessary.

The latest version is shown in figure \ref{fig:The-caterpillar-robot}.
It is also available in thingiverse%
\footnote{http://www.thingiverse.com/thing:8559%
}, along with some videos showing how it moves.


\subsection{UniTrack and F-Track}

%
\begin{figure}
\begin{centering}
\includegraphics[scale=0.64]{eps/unitrack}
\par\end{centering}

\caption{Unitrack (left) and F-track (right) robots\label{fig:Unitrack}}



\end{figure}


A different approach was taken by Jon Goitia. He focused on designing
robots with articulated tracks. The first design was Unitrack%
\footnote{http://www.thingiverse.com/thing:7640%
}, shown in figure \ref{fig:Unitrack} (on the left and in the middle).
It is an autonomous track driven by a hacked Futaba 3003 servo (the
same servo used for the Miniskybot). It consist of two wheels attached
to the servo and five standard o-rings used as tracks. Another o-ring
is used as the transmission system between the servo and one wheel.
Unitrack is also parametric, therefore the wheel's diameter and number
of o-rings can be easily changed. This innovative design was for one
month the first most popular thing on thingiverse, which is not easy
to achieve (currently there are more than ten thousand things!). 

Once Unitrack was fully functional, the F-track robot was created,
shown in figure \ref{fig:Unitrack} (on the right). It consist of
four articulated independent Unitracks joined to a body. This design
is an example on how the creativity emerges from some students when
they are stimulated.


\section{A new design paradigm: evolutionary robots}

Our new robotic platform combines two important features. On one hand
it is open hardware, so that anyone can study, modify and distribute
the robot. On the other hand the robot is printable making it very
easy for the people to materialize it. The result is that anyone in
the wold with access to Internet and to an open-source 3D printer
can copy the robot, improve it or create derived design.

These features allow the emergence of a new design paradigm in robotics:
Evolutionary robots. The robots can now be evolved by the community
in the same way the open source movement creates and maintain in a
distributed way new software applications, such as the Linux kernel,
gnu tools, wikipedia, firefox and so forth. Now it is possible to
bring these ideas into the robotics world.

In the previous section we have shown the derived robots created by
a group of local students from the Miniskybot robot. It is difficult
to imagine and foreseeing the wonderful robots that can be developed
by thousand of people around the world collaborating together. 

With the Miniskybot robot we have planted the seed. We have already
gotten some indications of the potential of this idea: some weeks
after the Miniskybot were published on thingiverse, at least three
derived design were built. The first was printed by people from Makerbot
at the RoboFest 2011 in Baltimore, the second at the FUBAR hacklab
space in New Jersey. They are using Roboduino as electronics. The
third one was built by CW kreimer%
\footnote{http://www.youtube.com/watch?v=2EqvuPXYKf0%
} for teaching robotics at the Pittsburgh boy scout high tech camp.


\section{Results}

%
\begin{figure}
\begin{centering}
\includegraphics[scale=0.59]{eps/Miniskybot-physical-parts}
\par\end{centering}

\caption{The MiniSkybot robot printed in red ABS\label{fig:The-MiniSkybot-robot}}

\end{figure}


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 MK5 extruder and a heated build platform. It
is very affordable with a total cost of 680¤.

All the parts have been printed without raft. The software used was
Replicator-G 0023 with Skeinforge 35. In figure \ref{fig:The-MiniSkybot-robot}
a red prototype is shown, along with all the parts needed for assembling
the robot. 

The total printing time is 2 hours and 50 minutes and the total robot
cost is around 57¤, as shown in table \ref{tab:Printing-time-cost}.
It can be seen that the cost of the chassis (the printable parts)
is marginal: less than 1¤. Therefore, the robot cost is only determined
by the cost of the electronics, motors and sensors.

%
\begin{table}
\begin{centering}
\begin{tabular}{|c|c|c|c|}
\hline 
\textbf{Parts} & \textbf{Printable} & \textbf{Printing time (min)} & \textbf{Cost (¤)}\tabularnewline
\hline
\hline 
Wheels & yes & 2x24 & 2x0.05\tabularnewline
\hline 
Battery compartment & yes & 30 & 0.07\tabularnewline
\hline 
Front & yes & 30 & 0.07\tabularnewline
\hline 
Rear & yes & 16 & 0.04\tabularnewline
\hline 
Battery holder & yes & 14 & 0.03\tabularnewline
\hline 
Castor wheel part 3 & yes & 12 & 0.03\tabularnewline
\hline 
Castor wheel part 2 & yes & 6 & 0.01\tabularnewline
\hline 
Castor wheel part 1 & yes & 4 & 0.01\tabularnewline
\hline 
Wheel O-rings & no & -------- & 2x0.5\tabularnewline
\hline 
Castor Wheel O-ring & no & ------- & 0.4\tabularnewline
\hline 
SRF02 ultrasound sensor & no & ------ & 11.8\tabularnewline
\hline 
Skycube board & no & ------ & 20\tabularnewline
\hline 
Servo Futaba 3003 & no & ----- & 2x9\tabularnewline
\hline 
4 AAA batteries & no & ----- & 2.5\tabularnewline
\hline 
Nuts and bolts & no & ---- & 2.5\tabularnewline
\hline 
\textbf{Total:} &  & \textbf{170 min (2h, 50min)} & \textbf{56.6¤}\tabularnewline
\hline
\end{tabular}
\par\end{centering}

\caption{Printing time and cost of the MiniSkybot v1.0 robot\label{tab:Printing-time-cost}}

\end{table}


Although this kind of 3D printers are not meant for production but
for prototyping, 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
\ref{fig:Miniskybot-group} a group of six Miniskybots is shown, printed
in different colors.

%
\begin{figure}
\begin{centering}
\includegraphics[scale=0.6]{eps/Miniskybot-group}
\par\end{centering}

\caption{A group of six MiniSkybot robots (v1.0) in different colors\label{fig:Miniskybot-group}}

\end{figure}



\section{Conclusion and future work}

Using the latest open source 3D-printers a new printable robotic platform
has been designed, built and tested. Our results confirm the viability
of these new printable robots. They offer new important features for
educational purposes. First, they are very flexible where 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 thoroughly 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 can be printed
per day.

As a future work we are planning to continue evolving the robot in
collaboration with our students, designing new parts for adding more
sensors as well as creating new derived robots. Currently we are working
on a new electronic board, with the same size than the Skycube but
compatible with the Arduino software that is becoming more and more
popular. In addition, we are developing a new idea on how to design
mechanical parts using object oriented programing. We have called
it as \emph{object oriented mechanics language} (OOML). 


\section*{Acknowledgements}

We would like to thank Prof. Luis Moreno, head of the department,
for supporting this educational initiative. Also we would like to
thank all the students who have been involved in building our 3D printer
MADRE. Special thanks to: Olalla Bravo, Jon Goitia and Daniel Gomez
for their great contributions to the Miniskybot Robot.

\bibliographystyle{plain}
\bibliography{bibtex}

\end{document}
