What is a planetary gear used for

[andythenorth]

21 minutes ago, aminnich said:

I still don't 100% understand how it changes the gear ratio, but it doesn't matter.

Imagine taking a regular 24t or 40t gear.  

Then slice (in imagination) a thin strip with the teeth from the outside of the gear.  

Then take the strip, and make it into a circle with the teeth on the inside, so you have an inverted gear.  

Meshing either the regular gear or the inverted gear with a smaller gear will change the ratio. 

Edited February 25, 2017 by andythenorth

[aminnich]

That makes sense, I didn't realize the turn table was acting as a gear (I mean yes it is a gear) but I thought it was just a place holder for the smaller gears. 

Thanks for the explanation 

[Burko-uk]

A planetary set up kind of has three "Axles" in one reduction stage. The Sun (single central gear) the Planets (Typically three gears inbetween the Sun and Ring) and the ring. The biggest gear reduction is between the sun and ring, so you fix the planet gears (Making them effectively idlers, with no effect on the overall ratio), drive the sun, and your output is the ring, going very slow with very high torque, hence, popular for winches.

Alternatively you can fix the ring and use the carrier for the planet gears as the output, keeping the sun as the input. Electric low line winches tend to use a two or three stage planetary 'box like this, with the ring teeth cut out of the casing.

[Imanol BB]

1 hour ago, Burko-uk said:

A planetary set up kind of has three "Axles" in one reduction stage. The Sun (single central gear) the Planets (Typically three gears inbetween the Sun and Ring) and the ring. The biggest gear reduction is between the sun and ring, so you fix the planet gears (Making them effectively idlers, with no effect on the overall ratio), drive the sun, and your output is the ring, going very slow with very high torque, hence, popular for winches.

Alternatively you can fix the ring and use the carrier for the planet gears as the output, keeping the sun as the input. Electric low line winches tend to use a two or three stage planetary 'box like this, with the ring teeth cut out of the casing.

I have a winch which has 3 stages of planetary gears, i have seen the motor spinning very very fast, but because of the insane gear reduction the drum of the winch spins very slowly, that is why winches are so powerful, and this post also made me remember that other great feature of the planetary gears is the ability to change the output direction by braking the sun gear, the planet gears, or the ring gear, which is very helpful for the automatic gearboxes while selecting the speeds and the reverse and still maintaining a low space consumption, and i think that some Unimogs use them to achieve " Super Crawler Speed".

[syclone]

Somewhat late, but this video just got published. The channel in general is worth checking out.

 

[Imanol BB]

Thanks @LXF, the video and the channel are indeed worth to look, there are many cool videos, including some about automatic transmissions with planetary gears.