I got it working with Eggduino. Really cool firmware. Works like a charm. Just two little modifications in eggbot.py and in eggbot_scanwin32.py and you can control the spherebot/eggbot/eggduino directly from within Inkscape.
I described the changes to be made here. Also read the readme from the developer for the other change in eggbot.py.
These modifactions are only needed for Windows computers. Mac’s find the Eggduino without modification.
I still need to calibrate stuff and find out how to mount the egg but it works now. Also the pen arm could need some modifications so it is less jittery.