What ratio do planetaries rotate at in a gearhead?

[mmagliaro]

So, in repairing an engine for someone (a Hallmark brass 2-10-4, to be exact), I decided to remotor it
with a gearhead motor.   

As I look in the back of a 4:1 gearhead at the 3 planetaries, I find I am confused about how these exactly rotate.
If it's a 4:1 ratio, how many time should each planetary rotate on its own little shaft for the output shaft to
make one complete rotation?

[Chris333]

Guess you could count the teeth 

[Chris333]

The Gizmozone gearheads  make it easier to take out a whole stage in one piece and spin it around the pinion. You'd still have to count though, and they are 5:1 I think.

[mmagliaro]

Chris,
Thank you for the pictures.  Those help.

But HOW do I count teeth?  The pinion on that Faulhaber in your picture has 12 teeth on it.
The planetaries look like they have 12 teeth.

So.... how does that work out to a 4:1 ratio?

[victor miranda]

the output ratio depends on what you use to drive the output.

the planets or the ring....

and then... I think the ring is a straight count pinion to ring teeth.

the planets I recall are calculated by the ring minus the pinion
and then to the planet teeth...

gunna have to look that up now that I have opened my mouth.

victor

[GaryHinshaw]

Does this help?  This site also has some animations of three possible operating modes.

[Chris333]

/>In the comments the one guy knows the ratio.


http://science.howstuffworks.com/transport/engines-equipment/gear7.htm

[Chris333]

So there is no way to post a Youtube link without it showing up as a player?

[timwatson]

I'm not sure on the ratio but I know from my motor tests if you take one ring out and put it back together it seems "about right". Hardly scientific but every little bit helps right? In re-reading ALL the posts this is just what Chris said. Blah.

Sorry.

Sitting down.

If you'd like to play with some inexpensively I have used this one (it's very fragile and very tiny). http://www.ebay.com/itm/Tiny-Electric-Motor-With-Reduction-Gear-Drive-/270367248573?pt=LH_DefaultDomain_0&hash=item3ef324d0bd

Taken apart:

This may be smaller than needed. I needed a very compact solution for a railbus mech.

And there there is this one:
http://www.ebay.com/itm/221457499246?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

[Chris333]

Pretty sure you take how many teeth are on the outer gear and dived by how many teeth are on the pinion. I don't think the planets matter at all. So if the pinion was 12 teeth the outter ring would be 48 teeth to get 4:1.

[Chris333]

Pretty sure you take how many teeth are on the outer gear and dived by how many teeth are on the pinion. I don't think the planets matter at all. So if the pinion was 12 teeth the outter ring would be 48 teeth to get 4:1.

guess this is all wrong...

found this: http://www.phidgets.com/docs/Stepper_Motor_and_Controller_Primer

[timwatson]

That last link is very informative Chris. So thats why removing a stage seemed like it sped up things. The ratio was halved. Makes sense.

[victor miranda]

If it makes any difference chris, I got the ratio calculation wrong also.

I will point out that the output ring or planets is a different ratio.
one of the early auto transmissions used a planetary gear system to get three ratios
... and the sturmey-archer bicycle hub...

1 to 1 -- lock the whole thing up
lock the planets and lock the ring.

don't know the order however.
 
nor the ratios...

[Chris333]

That last link is very informative Chris. So thats why removing a stage seemed like it sped up things. The ratio was halved. Makes sense.

Yeah if it is a 4:1 gearhead and there are 2 stages it is then 16:1, 3 stages is 64:1, 4 stages is 256:1.  Anything more than like 5:1 is too much for N scale locomotives. A pretty crappy N scale ratio would be like 15:1. Add a 5:1 gearhead and the total ratio is now 75:1.  Worm/worm gears are also reduction. The worm gears on these axles have 15 teeth and the one on the end of the lay shaft has 14 teeth. So it has 210:1 ratio!
https://picasaweb.google.com/ErieChris333/HOn30#5248282405555602210

[timwatson]

In looking for some other sources for larger planetary gearboxes in plastic I found this little guy. For $9 the gear heads alone would be worth it since you get 5 of them.

http://www.ebay.com/itm/5pcs-Hollow-cup-Dc-3V-5V-6V-gear-motor-Planetary-gear-reducer-micro-motor-robot-/111427884858