To get some more artistic variety in the simulated rotary harmonograph output, we introduce a dampening, i.e., causing the pen and table to run down as though from friction. Also, we can nudge our simple ratio slightly, to add a small element of discord or imperfection.
Here is the adjusted function:
(define (rot ang/tunit t phase dampfact) (* (make-rectangular (expt dampfact t) 0) (expt ei (+ phase (* ang/tunit t)))))
With very fine control of the ratios, dampening factor, and number of samples, we can produce a variety of effects. (I’m guessing this would be much more difficult with a physical harmonograph.)