Summary

This project allows you to write on the spherical surfaces such as Christmas balls or eggs.
This machine is in fact known in the internet as Eggbot or Spherebot .

More info
http://www.open-electronics.org/spherebot-reloaded-customize-your-xmas/

Video:
http://www.youtube.com/watch?v=Ofufxmm6wd4

Instructions

The mechanics
The mechanical part is composed of parts made with a 3D printer , by some threaded rods and a pair of bearings.
Compared to the versions available on the net, our spherebot presents "print area" greater , so you can draw even on christmas balls with a diameter of 7/8 inches.
You can download and modify also Sketchup files to make it bigger or smaller.

The software
As most of the numerical control machines also our spherebot is able to handle the codes Gcode.
A usable software can be downloaded from here or Github
https://github.com/thunderbug1/Spherebot-Host-GUI
and has a nice user interface. The software is very intuitive and also allows you to move all three engines to properly position the marker.

Getting the Gcode file
To be able to turn your ideas into prints, need to go through a simple sofware conversion, capable of transforming into Gcode your design or text.
A free software that can help you is INKSCAPE
http://inkscape.org/
The special feature of this software is that it can be modified and adapted to the various needs through scripts written in python .
Once again the comunity helped us and made available an extension to export our image vector in Gcode. In the download section you can download the plugin, which is the same that are available on Github
https://github.com/martymcguire/inkscape-unicorn
Installation is simple, just copy the files located under the SRC folder, under the extensions folder of Inkscape , usually C:\Programfiles\Inkscape\share\extensions
Restart Inkscape and the extension is installed .

To transform a written into Gcode is necessary create a path that our marker must follow in order to achieve the inscription. From the Path menu select the item from the object to track.
Now save the file in Gcode: from the menu File select Save as and save the file with the extension *.Gcode .
Confirming it will open a window where we can define some parameters such as the speed, the angle that defines the pen raised , lowered , and other parameters .

The electronics
The spherebot is composed of two stepper motors and a servo.
A motor is used to rotate the ball on the axis , the second motor allows to move the marker around the circumference of the sphere.
The servomotor finally serves to raise and lower the pen.
In addition, to allow anyone to easily edit the software without the need for programmers or compilers would be ideal to have a board based on the Arduino .
All of these needs are met by the board of the printer 3Drag.
http://www.open-electronics.org/a-new-board-for-the-3drag-theres-more-than-sanguinololu/
http://www.open-electronics.org/?s=3drag

The firmware
Being an open source project did not have to write all the code, but it was enough to find someone who worked there and make any changes.
A big hand has given it Eberhard Rensch
http://pleasantsoftware.com/developer/3d
We desired, however, that the sketch also worked with the latest Arduino IDE (version > 1.0) so we had to modify it a bit. In the Download section you will find the firmware.
The sketch is concerned directly manage the two stepper motors and servo according to the commands received GCode via the USB port. The combination of the three engines allows you to write on the ball without any problems.

More info
http://www.open-electronics.org/spherebot-reloaded-customize-your-xmas/

SphereBot - Full Project