Cycloid Pen Plotter

admin | 05.03.2026

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Create random geometric patterns (cycloids) using a 3D printed CoreXY style pen plotter. This model is an update to my Etch A Sketch, which was one of my favorite projects. Unfortunately, the strings often break in the original, making repairs difficult.

Mechanical drawing machines have a long history, with early versions such as the Marvelous Wondergraph and Hoot Nanny, as well as the popular Spirograph. Modern versions, like the Cycloid Pro, can be found on Joe Freedman's website (LEAFPDX).

The Arduino program simulates a drawing machine by placing random gears and connecting arms around the drawing area. Instead of rotating the paper, the gears and arms rotate around. I designed it to work on a dry erase board for easy cleanup, and you can also draw on paper by attaching it with magnets.

The drawing area is 356mm x 445mm (14" x 17-1/2"), but it can be easily scaled. Three different designs for the pen holder are included: with a servo lift, without a lift, and angled down for wall mounting.

Note: Build at your own risk. Stepper motors can get very hot if not properly sized. I am not responsible for any issues or failures that may arise.

Keep in mind that results may vary: you might get simple or even unattractive drawings, but occasionally you'll create something truly impressive. Have fun!