While a harmonograph with one 2D arm and one 1D arm would seem to be simpler than one with two 2D arms, in fact many of the images it produces are more complex. The reason is that while a machine with two, 2D arms has more freedom of motion, the fact is that both arms move with similar types of movements. With a harmonograph with a 1D/2D combination of pendulums each arm follows a fundamentally different path. It's true that a harmonograph with two, 2D arms could be started with one arm moving in a straight line. However, friction in the joints quickly transfers energy from the arm moving in a circular path into the arm moving in a straight line. In short order they are both moving in circles.
The following images all have the drawing platform locked so it doesn't move. One pendulum is started swinging in a circular motion while the other is constrained to move in a straight line. The 1D pendulum is shimmed by varying amounts to create a range of traces.
The first image has the 1D arm shimmed 0.37 inches.