I've been working on a drawing robot pen holder for my PolargraphSD powered robot. If you like reading about awesome robots, you'll probably want to check out a ridiculous amount of posts on the topic on my site. http://makerblock.com/Designed in OpenSCAD, I tried to use what I learned about drawing machine pen holders ( http://makerblock.com/2013/03/a-study-of-drawing-robot-pen-holders-and-design-considerations/ ) to choose the best qualities of the bunch ( http://makerblock.com/2013/03/ideal-qualities-in-a-drawing-robot-pen-holder/ )I'm still working on this design, discussed here ( http://makerblock.com/2013/03/enough-talk-finally-a-pen-holder/ ), please expect it to change and for there to be some improvement in it.