The repeat accuracy of such a simple mechanism is absolutely amazing. Never in my life would I have guessed that you could make some many reversals without some accumulating error somewhere.
This bites pretty hard on hektor, a graffiti robot:
<a href="http://hektor.ch" rel="nofollow">http://hektor.ch</a><p>I met the kid who built this, year ago. He is a seriously rad ex-demo scene hacker, now art school prof. Lots of other good projects there worth checking out.
If you're into this kind of stuff check out HackerThings (I made it, not for profit):<p><a href="http://hackerthings.com/" rel="nofollow">http://hackerthings.com/</a><p>It's for hardware and electronics hackers (and programmers, of course). A good book on things like this is Programming Interactivity at <a href="http://www.sparkfun.com/products/9415" rel="nofollow">http://www.sparkfun.com/products/9415</a> (that's the kind of thing you'll find on HT).
There's a brief summary of something vaguely similar I made during my degree here: <a href="http://joefreeman.co.uk/blog/2009/09/lineographic-interpretations-of-images-with-an-etch-a-sketch/" rel="nofollow">http://joefreeman.co.uk/blog/2009/09/lineographic-interpreta...</a> (Lineographic Interpretations of Images, with an Etch-a-sketch)
The use of polar coordinates is interesting, and it makes the images look a lot more interesting than a simple X/Y. (Probably less mechanical strain too.)