The radius of the rolling circle is 1/n th that of the fixed circle. dn is then the number of rotations GGB will consider before resetting the positions. By default, n is an integer. To include fractions, increase dn. Check "allow irrational" to change the radius smoothly. Trace applies to the diameter of the rolling circle.
Notes: The purple and green curves are arbitrary intersections among the given objects (and are not fixed arms). I think I found what I was looking for. The smooth (continuous) change of a deterministic, cyclic system is altogether a separate question from mathematical periodicity.