Hey guys. Here are some references for planetary gears.
You can find a simple example of planetary gears here: https://youtu.be/nt1_jQM5JWA Be sure to read the entire description.
This is an army training video explaining how multiple sets of planetary gears can be combined: https://youtu.be/SrkzaQRDtuM
And just for fun, here is a video of some wooden, non-circular planetary gears: https://youtu.be/AdXZbGehwzs