planetary gear calculation has me stumped...for now at least...

[Workinginwood]

Greetings from Puget Sound! I've been looking at this program for awhile now, every now and then thinking I'm going to be cutting gears, then I get sidetracked or I need to tweak the cnc machine, or .... you get the picture! I'm glad I finally have a little project on hand that gets me learning how to use this program!  :)

I am trying to figure out the equation for planetary gears. I have figured out the simple equation, with help from this and other forums, to get the correct number of teeth on all three gears.
Ring=Planet+Planet+Sun. There is a thread in this forum that says all gears need to be even.

One forum suggested that the planet gear was a "traveler" or "idler" and didn't fit into the equation for the gear ratio calculation. That is not the case.

I'm shooting for a 12/1 ratio using 2 planetary gear sets  working at a 6 to 1 ratio. One on top of the other.

This is what I did and what I ended up with:

I cut the pieces out of some 1/4"ply to test.

For the first 6 to 1 set I used 72,30,12,30. This is ending up taking not six revolutions but seven of the sun to move the next gear tied to the centers of the three planet gears.

The planet gears have a relation that I am vaguely (almost kinda) getting my head around.

The numbers add up but using that information to come up with a solution is not happening. 72+12 = 84

7 revolutions is not by chance. Everything adding up to a multiple of 12 is not a chance. The planets have to fit in there somewhere but I just don't see where.

Any clues? I'm looking for an equation that I can use to figure this thing out.

Thanks for your help.

[ArtF]

Hi:

Have you read this thread?

http://gearotic.com/ESW/FavIcons/index.php?topic=1319.0

It has a discussion on planetary ratios and how they stack. I understand the confusion
though, each time I answer a question usch as this I find I need to recheck how that works
exactly..

Also, check this page, it explains the variations on the ratio depending on the locked axis..

http://science.howstuffworks.com/transp ... /gear7.htm

Art

[Workinginwood]

Hi Art,

Thanks for the links. I'll go over that tomorrow and cut some more pieces and play around a bit with things to get something in my hands that I can play around with.

My original explanation was wrong. I think the sun gear to ring ratio IS correct. I think if I stack two more of these assemblies on top of this one I'll get my desired rate of reduction.

What I am going after is getting the "PLANET CARRIER" to be the 6 in the 6 to 1 ratio and the 1 being the ring. Right now, it is a 7 to 1 ratio. 3 planets. 72 ring, 30 planet, 12 sun.

Karl

[ArtF]

Karl:

Your ratio is

1 + 72/12 = 7

  Your probalem is you need to add 1 to ratio you determine. Make the ring 60 and you have

1+ 60/12 = 6 as your ratio...

  Youll find the graph on that link allows you to see the ratios depending on the lock.. carrier or sun..

Art