Gears

[Stoyboy]

I know i am kinda new here but i didnt know where else to ask this question so here goes.

Is there such a gear that has teeth both on the outside and on the inside of the gear, i have looked online and i have no idea where to find them if they exist.

[Admin]

not to my knowledge . . . if one does exist, its probably rare and expensive . . .

unless a planetary gear or harmonic drive gear counts . . .

a timing belt can have teeth on the inside and outside . . .

what are you trying to do?

[JonHylands]

The specific kind of gear you're looking for is a ring gear. There seems to be two types, internal and external.

If you could find one of each that were the appropriate size, you could join them to form what you're asking for...

These guys seem to have both kinds: http://www.sdp-si.com/eStore/CoverPg/Gears.htm

Specifically:

https://sdp-si.com/eStore/Direct.asp?GroupID=225
https://sdp-si.com/eStore/Direct.asp?GroupID=203

You might be able to find a pair that would fit together...

- Jon

[annoyin_kid]

how would you connect the gear to the shaft if there are teeth on the outside and the inside?

[polar bear6]

how would you connect the gear to the shaft if there are teeth on the outside and the inside?

i want to know that too

[JonHylands]

Not all gears are for attaching shafts. If you envisioned this as a planetary gear, the "holding power" could come from the sides, where it was held between two bushing plates.

I have no idea why you would want one, though...

- Jon

[Stoyboy]

I want to use it as a planetary ring so that i can set a few of them in sequence and then be able to connect a driving gear at the top of the ring. If i connect to the first ring in the set i get lets say 1:3 and if i connect to the second i get a better ration lets say 1:9. thats whats why the ring needs the inside teeth to make it spin and the outside so that i can use that ration to drive other things.

[dunk]

let me see if i correctly understand what you are talking about.
would a simplified version with only one ring gear be set up like this:
the motor's gear is driving the outside of the ring gear.
the inside of the ring gear is driving the output shaft's gear.
right?

lets put some numbers in this to see if i understand what you are trying to do correctly.
lets say you have a motor connected to a gear with 10 teeth.
a ring gear with 20 teeth on the inside and 40 teeth on the outside.
and a drive shaft (to connect to your wheels or whatever you are trying to drive) with an 10 tooth gear on it.

the motor will drive the ring gear at a ratio of 10/40 = 1/4.
the ring gear will drive the output shaft at a ratio of 20/10 = 2/1.
so, combining these 2, the motor is driving the output shaft at a ratio of 1/4 * 2/1 = 1/2 (or the motor turns twice as fast as the drive shaft).

is seems to me an inefficient way of doing things. stepping up the ratio, only to step it down again.
easier (ie, smaller and more efficient) to just do it with 2 gears.
or am i missing the point?

(anyone know a good, free package for drawing gears? i think we might need it here....)

dunk.
(will be thinking about gears all day now....)

[Stoyboy]

I think this might help......



The top gear is the output from the system....

The other gears are a planetary set, where the input is the planetary carrier, and output is the ring. Now if i put a bunch of these in sequence i can move the top gear to select which planetary ring to connect to giving me the different ratios

[Admin]

what gearing ratio are you trying to get?

might be easier to just buy a dc motor that already has a gear head with the ratio you want . . . or at least buy a preassembled gear head . . .

my attempts at gear assembly in the past have always had issues, so i tend to avoid it if possible . . .

[JonHylands]

So you're basically trying to build a planetary transmission... Very cool.

- Jon

[Stoyboy]

what gearing ratio are you trying to get?

might be easier to just buy a dc motor that already has a gear head with the ratio you want . . . or at least buy a preassembled gear head . . .

my attempts at gear assembly in the past have always had issues, so i tend to avoid it if possible . . .

I want to be able to switch that ration.

So you're basically trying to build a planetary transmission... Very cool.

- Jon

I think you might have the best explanation of what i am trying to do.