Harmonic planetary drive

thingiverse

This is a little mechanism I've been working on. It's a reduction gear. It's similar to a Ravigneaux gear in that it uses a planetary gear with different geometry along its length to achieve leverage, but it differs in where that happens. In this arrangement, the planets and sun gears have the same number of teeth along their entire length, but the to outside rings of the gear have different numbers of teeth. In this example, the sun and planet gears have 15 teeth. The lower (fixed) outer ring has 45 teeth, while the upper (output) ring has 42. That combination means that as the planet gears engage with both the fixed and the output rings, they are forced into alignment, and the output ring advances one tooth per rotation of the sun gear. This mechanism has a reduction ratio of 42:1.