Gearbox is VERY complicated to Calculate Differential Planetary, Harmonic

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Gearbox is VERY complicated to Calculate Differential Planetary, Harmonic

Post by Eduexpert on Mon Apr 10, 2017 6:41 pm

Hi Guys, Hopefully you can help me find answers to my questions.

It sounds like a simple problem and i know I will drive some people away by saying that i am trying to
calculate the gear ratio out of a planetary-style gearbox, but that is NOT the whole story! this is very similar to a harmonic drive.

The whole story is that a while back i came up with the idea of taking two planetary gearboxes and interconnected the planets,
i can do this in Fusion 360 by adjusting the module of one planetary gearsets until the center to center distance of the planets is equal between the two planetary's, and the reason i thought to do this is to get some very high gear ratios(100:1+) out of 3D printed plastic parts without using much of any bearings or hardware.

heres one that i have made in the past , i was not able to calculate the speed of anything at that time, and designed it without knowing the output gear ratios at all, now i have gotten a bit more educated on the subject, but still can't figure this out completely.

# of Planets 4
Sun #1= 26
Planet #1=38
Ring #1=102
Sun to Carrier Ratio: 4.9261 rotations of sun per revolution of carrier
Planet Gear Rotations per revolution around ring gear 2.6845

Sun #2 = 29
Planet #2 = 37
Ring #2 = 103
Planet Gear Rotations per revolution around Ring Gear = 2.7838

if you interconnect the planet gears between these two planetary gearboxes, drive Sun gear #1, and hold Ring Gear #1 stationary, What will the ratio between Sun Gear #1 and Ring Gear #2 be?

its too easy to calculate these when i keep the planet gears with the same number of teeth in both gear sets, but I think i could achieve much much higher gear ratios if i don't constrain my design like that. Thanks in advance!


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