I recently created a simple pen ploter on my reprap machine:

[www.youtube.com]

The pen mount is designed and printed by me, it uses rubber band to push the pen against the paper and a stepper motor to lift it. Here is a short video where you can have a better look at the mechanism: [www.youtube.com]
I use python for all the stuff: most of the things you can see on the video are just bitmaps which are converted to gcodes in such a way that they are drawn line by line. The trajectory of the rocket is computed using Newton's law of gravity.

In the near future i plan to extend it to use another pen so that drawing with to different pens independently will be possible, stay tuned!

Z-rods too slow for you? Any info on the carriage and other prints you're using?

... some ten years ago I've programmed a vectorizer for milling isolation-curves for PCB's on my CNC-mill, that searched the first point in a bitmap and then 'traced' the outlines of the found part by drawing a line to the next point while removing the last.

Today I'm simply importing the bitmap into Inkscape, let it vectorize and export the contours into my CAM for adjusting or add hatch or post-optimizing the tool-paths ...

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Viktor
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Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]