I had some problems in getting the Arduino to be found as a COM port by my pc. I found out that, as it seems, the designer of the Arduino Nano has forgotten to connect the Test Pin of the FTDI chip with ground. The solution of this is to do it yourself with a little solderbridge. Coincidentially the neighbouring pin is a ground pin :D . I unintentionally connected also a 3rd pin with the solderbridge but after a look in the datasheet I knew that it is ok and the additional pin has no important function. Despite this little flaw with the missing grounding I really like these little arduinos and they are also cheap enough to be left in a project.
After solving the problem it still didn´t work as I wanted it to work. the servo motor worked as it should but the stepper motors made crazy things. The pen motor made nothing until it was touched and then it suddenly accelerated until it reached the end. The egg motor suddenly rotated without a reason. First I tought about an unwanted feedback from the output to the step pin but as it turned out simply 2 wires of each motor were switched and this caused my problems. I didn´t thought that the motors would do anything if connected the wrong way but they teached me better xD.
The Firmware is based upon this
Because of the lack of a convinient host-side-program I decided to write the gcode-sender on my own. It was my first Qt-project but I´m quite satisfied with it. It may not be the most beautiful code but it works. In the future I will try to write more modular code for reusing.