The next week I was discussing SOLIDWORKS motion with a prospect and how it allows you to simulate complex motions and the Harmonograph came into my head (can you imagine a more complex motion than the above image?). So I made a first example, really simple, two pendulums, probably took all of 5 mins to create. 
In motion I added gravity and clicked run, although I left out the details that connect the pendulums to the drawing pen I was able to see the drawing was working by tracing a point on one pendulum with respect to the other pendulum. See how the curve moves with the pendulum on the left while tracing the path of the pendulum on the right.
After determining the system was working as expected (crawl, walk, run) I added a simple drawing mechanism. To reduce the modeling effort I replaced the wires linking the pendulum to the drawing mechanism with 2 simple equations. Now the system was quite recognizable, even to my 3 year old.
From there I had to try another version of the drawing machine I’ve seen with rotation (loved my spiralgraph so much I wore the teeth off). 
Of course there’s a point beyond Motion’s ability to simulate these really cool drawing machines. I’ve created a few cams over the years using this functionality. Basically what we do is simulate the desired linear motion, then trace that with respect to some rotating object and SOLIDWORKS motion with automatically draw out the required cam for your system. From there you can make that trace become a curve in SOLIDWORKS, simply extrude, rinse and repeat. So if you've ever needed a complex path created by the motion of objects in your design SOLIDWORKS Motion is the tool for you. Tim Newton Symmetry Solutions Inc