So off I went into a CAD design package to start designing a simple sun and planet gear arrangement driven by a geared motor I had sitting in my light painting tool kit. There were a few design challenges along the way, most notably how to connect the planet gear to motor mounted at the center of the stationary sun gear. Here are a few images of the final design. I used a 60 tooth sun gear and a 59 tooth planet gear to ensure a pattern would be generated.
From here it was 3D printing time for the parts. After around 18 hours of print time over several days I had all the parts to make the spirograph system. I did make one design mistake with the base of the device not clearing the motor terminal but I came up with a dodgy solution to that (it’s all about the super glue!). Here is the assembled unit picture I posted on Instagram.
So now for the first test. First issue I found was to get the battery pack and LED to stay in place. I never quite got a solution I liked but I did get it to stay put long enough to take some shots. The second issue was with the gear motor I was using. There is a grub screw to lock the final drive gear to the output shaft. For whatever reason it just kept coming loose after a few minutes of run time. I did manage to get it tight in the end but then the final straw that made me throw in the towel for the night was the whole unit itself falling over.
After all the set backs I did get a couple of decent sample shots in to prove out what I was trying to achieve. Here is the better of the two.
From this I think using a 60T x 59T system was a bit of a mistake as the pattern does not change enough on each orbit of the system. It seems a bigger ratio difference would have been better, say 60T x 47T or 60T x 37T. A range of different gears ratios like a real spirograph set would be ideal, and whilst not an impossible design challenge it would take a few iterations to get to a robust design.
Instead of gears I now have a somewhat different system in mind to work on next that uses multiple geared motors. It takes me a while to get these projects done due yo my own time constraint but watch this space. I will work towards getting it done over the next month. Time to buy some cheap servo motors to hack for this one.