Thwo years ago, or so, I've got a big cake of CD-R disks with inkjet printable
white surface. It turned out that my hp5150 mechanics are not strong enough to bend diskette on the same way as the paper.
To exploit the beautiful diskettes I've been thinking long ago on a circular plotter that is able to write text and draw simple pictures with a permanent marker pen.
Normal plotter writing head is lightweight to reduce the load on the movement mechanics. The pen up / pen down does not need heavy motor. Since NXT set does not contain such lightweight motor we were trying to keep the NXT motors fixed on the base. Resulting achitecture is built on the NXT turntable, pen up/down movement axle is lead through the turntable.
I've uploaded two MLCAD drawings here, will upload more drawings and photos also.
First picture is a general view of an earlier version (deliberately lacinkg most axles and pins).
Next picture is a refined pen up/down mechanics. Original design lifted up and pushed down the pen by motor force. This modification uses a pin to lift the pen up. Turning the black gear the ping lets the pen down by its own weight.