The Impossible Planetary Gear Fidget

This fidget uses planetary gears, it’s a great way to better understand how they work.

Demonstration 

If you hold the carrier(middle gear) and turn the sun(top gear), you get at 3:1 speed reduction. This ratio is a result of the 36 teeth on the ring gear divided by the 12 teeth on planet gears. If you hold the ring(bottom gear) and turn the sun(top gear), you get a 1:4 speed reduction on the carrier(middle gear). The is because the much larger diameter ring gear is moving faster than the smaller sun gear. The equation works out to be the 36 teeth of the ring gear divided by the 12 teeth of the planet gear plus 1. If you hold the sun gear and spin the ring gear and the carrier, there is no reduction and it acts like a bearing

Prints in place with no supports!

Printed on the Mulcore