When I got the Ultimate Builders set, it came with instructions for a plotter. Mind you, the RCX had no integrated rotation sensors, so it used a lever rotating against a touch sensor. It even used a complicated construction to drive a pneumatic pump with one motor.
It came with a program to write “LEGO”, which I did not understand, because it was huge. And it didn’t work either, but that turned out to be because of a broken sensor… after I took the plotter apart.
I just found the video of a “Lego Master builder” introducing the model.
Anyway, a plotter was on of the things on my list that had to happen properly someday. The one you see here is my third attempt. The first two where too fast, too bulky, and had a very feeble arm holding the pen.
I actually made this model before the NXTbike, but I messed up the building instructions, so I had to do it again. I can’t recommend Lego Digital Designer for any serious Technic building, use LDraw instead.
The first thing I did, even before my first attempt, was writing a virtual plotter, so I could quickly code up the alphabet. I wrote the software in Python, so that I could use the Turtle module for the virtual printer, and nxt-python for the real job. The software can be found on Github.
I made this model before I realized I should minimize the use of non-NXT parts. Ironically, this model uses a few parts from the Ultimate Builder set, but easy workarounds exist for most parts. Check the parts list before you buy.