NXT Drawbot

When I saw this drawbot, I immediately thought it was something I should be able to recreate with Lego Mindstorms. And so I did. The idea is simple, there's a pen suspended on thread from motors in the corners. When the motors wind or unwind the thread, the pen moves and draws a line. The rest is a simple application of the Pythagorean theorem to move the pen where we want it.

When watching other drawbots on YouTube etc. I was surprised to see they were able to achieve a level of precision that allows them to recreate pictures by effectively drawing each of their pixels with clever patterns. My bot clearly lacks such precision. I think the main reason for that is the friction between the pen and the drawing surface. Each time the pen is about to start moving, there's a noticeable moment before it breaks away from the static friction. That makes the bot incapable of very small precise movement. There's another source of imprecision - since the radius of the spools that the threads are wound onto is small, the difference in radius when there is no thread wound and when there is a lot of thread wound on the spool is non-negligible.

Here are some more pictures of the bot.