How to Make a Three-Pendulum Rotary Harmonograph

A harmonograph is a mechanical device that uses swinging pendulums to
draw pictures, believed to be originally invented in 1844 by Scottish
mathematician Hugh Blackburn.

Two lateral pendulums swing back and forth at right angles to each
other with arms connecting to a pen.  One moves the pen from side to
side, and the second moves it from front to back on the paper.  A
third "rotary" pendulum moves the paper by swinging on any axis or in
circular motions, while the pen is drawing on it.  The combined
motions of all three pendulums generate the resulting drawing.

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