This was just a fun project that I have seen many people do, so I figured I should give it a shot. I purchased a small Etch-A-Sketch and replaced the knobs with custom ones that connect to two servo horns. Both the horizontal and vertical axes are driven by continuous rotation servos.
The circuit for this project is very simple. There is a Basic Stamp 2 mounted on a board on the back of the Etch-A-Sketch. A ribbon cable runs to the board in the front which contains all of the controls. I placed a small analog joystick to the control board along with a few buttons and LED's.
The program as it stands at the moment is very simple as well. Both axes of the joystick are potentiometers. Their positions are simply read in, converted to usable values for the servos, and then sent out to the servos.
Just as an experiment, I actually drew a heart in MSPaint, zoomed in to the pixels and broke the path down into up-left-up-up-down-right... etc. A couple sheets of paper later I was able to load the pattern into EEPROM. Now whenever the button is pressed on the control board, the Stamp will read the EEPROM direction by direction and move the servos accordingly. Drawing the heart does not work as well as if I would have used stepper motors, but when drawing manually it works very well with analog speed control.