the coil you're referring to in the video of the robot drawing the dinosaur was used as a weight to hold the sharpie down in the holder, so that the sharpie could write on the paper despite the robot not moving exactly perfectly coplanar with the paper on the floor. when the robot is in pen-up Z position, the pen is resting at the bottom of the holder but still not touching the paper. When the robot moves to pen-down Z height, the pen is resting on the paper with the coil's weight pressing it down and it's writing. It was a kluge. also a sharpie is tapered so it doesn't work very well because it's sloppy in the hole, which is in a 3d printed plastic thing i made just for holding sharpies. We need markers that are not tapered. -jake On Wed, 20 Apr 2016, Cere Misc wrote: