While playing with gear design again, I thought I could add a second row of planets (or are these moons?) to get some interesting behavior:

• If you lock the ring in position and rotate the sun gear, the planets rotate in the other direction around the sun.
• If you hold the sun gear steady and rotate the ring, the planets move in the same direction as the ring, but a bit faster than the ring.

Also try the little hand crank (or two) for a bit more fun →

If you liked this one, you might also like The Counterintuitive Gear MkII with more and faster planets.

Printing: 

0.4mm nozzle, random seam placement, otherwise standard settings.
I also used archimedean chords top&bottom infill.

This is a print-in-place model, no assembly is needed, but a well-tuned printer.