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### Topic: Help Me Calculate a Differential Planetary Gearbox? (Read 1 time)previous topic - next topic

#### Sparkyman

##### Mar 27, 2017, 06:59 am
Hi Guys, sorry for this not being entirely Arduino related, but i do control the motor that drives the gearbox with Arduino!

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 gearset 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 http://www.thingiverse.com/thing:2054378  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?
Full Time Electrician, Part Time Tinkerer.

#### Sparkyman

#1
##### Mar 28, 2017, 07:20 pm
Wanted to mention that I have solved this with help from another forum, but I would rather not post the solution at this time
Full Time Electrician, Part Time Tinkerer.

#### MarkT

#2
##### Apr 17, 2017, 12:16 amLast Edit: Apr 17, 2017, 12:24 am by MarkT
I don't understand your gear setup - you claim to hold ring 1 stationary, connect planet 1 to planet 2, and
drive sun 1.  That's underconstrained so there is no unique solution.

Or are you just looking at the first epicyclic stage?  Simply transform to the planet-cage frame and
the maths is easier.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

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