This may be one of the cheapest and easiest CNC drawing machines you’ll find

CNC plotters are a lot of fun to build and use, as they teach mechanics, electronics, and how G-code works. However, traditional Cartesian machines often require expensive components such as linear rods and ample amounts of bearings to move in just two axes. YouTuber DAZ Projects set out to change that by assembling a form of a Polargraph to draw pictures with great detail. The idea is simple: use a pair of stepper motors to alter the length of a string on two sides that controls where the toolhead goes. 

He started by 3D printing stepper motor mounts, a few pulleys for the string to wrap around, and the pen holding/lifting mechanism. Both 5V stepper motors plug into a generic Grbl CNC shield and are driven by a couple of A4988 modules. The servo is powered directly by an Arduino Uno, and its job is to adjust the pressure the pen applies to the page to define how dark the lines are. 

Once the custom firmware written by the Polargraph’s creator, Sandy Noble, was flashed to the Uno, DAZ connected it to his computer which was running the Polargraph control software. In here, the program takes an image and outputs a series of toolpaths for the Uno to convert to motor movements. You can see how DAZ constructed and used the device below, as well as the find the code on GitHub and 3D design files on Thingiverse.