I designed this fully 3D printed solar system model that updates itself once per day.

All eight planets are mounted on separate rings, and the Moon is included as well, showing the correct phase. The whole mechanism is driven by a single motor and runs a short sequence to position everything.

The interesting part is that it doesn’t use a traditional gear train. All rings rotate freely and are picked up and positioned one by one, which keeps the design relatively simple.

Getting it to run smoothly was probably the hardest part. The rings sit in shallow grooves, so sanding and print quality make a huge difference. If a ring doesn’t spin freely for a couple of rotations after a push, it won’t work reliably.

Here’s a short video of it in action (the movement looks simple, but it’s oddly satisfying to watch):

https://www.youtube.com/watch?v=yZWWDG4Uw-U

If you want to build one yourself, I’ve put all files and instructions here:

https://www.instructables.com/Meridian-Orrery