Making a "Planetary Gear Set" using a 3D printer and PLA material

[Joorge]

TL;DR Summary

Obtaining the same speed in the sun and ring gears, while moving in opposite directions in a planetary gear set.

I want to create a set of planetary gears using a 3D printer and PLA material. I'm designing them with the help of Autodesk Inventor 2020 since my knowledge in this area is quite limited. The gear set consists of a ring gear, a sun gear, and 2 planet gears. The sun and the ring gear rotate in opposite directions, while the planet gears remain stationary. I need the rotation speed of the sun and the ring gear to be the same. I mean, one turn of the ring coincides with one turn of the sun, if that's possible, which honestly I have no idea.

I asked ChatGPT, and it tells me the following:

"The basic condition for a functional planetary gear with a 1:1 gear ratio is that the sum of the number of teeth on the ring gear plus twice the number of teeth on the planet gears is equal to the sum of the number of teeth on the sun gear plus twice the number of teeth on the planet gears. Mathematically, this is expressed as:

C + 2P = S + 2P

Where:
C = Number of teeth on the ring gear
S = Number of teeth on the sun gear
P = Number of teeth on each planet gear

This means that the total number of teeth on the ring gear and planet gears must be equal to the total number of teeth on the sun gear and planet gears. By satisfying this equality, the gear ratio will be 1:1, allowing the ring gear and the sun gear to rotate at the same speed and in opposite directions."

Is this true? I'm not sure I can fully trust the AI on this matter, because it gave me a lot of wrong answers before I got to this text, which does seem coherent to me.

Thank you and regards.

 

[Joorge]

Indeed, I'm asking again and it's telling me the last answer I've posted is wrong. I'd appreciate if you can tell me the "truth", LOL. It may not be possible for one turn of the ring to coincide with one turn of the sun, but I guess is right, as long as the ring and the sun have the same amount of teeth. Please let me know.

 

[A.T.]

To keep the planets stationary the tangential speeds of sun and ring need to be equal but opposite. If you want their angular speeds to be equal and opposite too, their radii would have to be equal, so the planets would need to be of size zero.

 

[Joorge]

Thanks for your answer. Honestly, I don't know that much about tangential and angular speeds. What I need is the ring to turn once at the same time as the sun does, but in opposite directions, hence the planetary set. I understand this is possible as long as the ring and the sun have the same number of teeth, and the problem will be the diameter of the ring to be big enough to hold the sun and planets. It won't be possible for certain sizes. Do you think I'm right?

 

[A.T.]

It won't be possible for certain sizes. Do you think I'm right?

See my post above. It won't be possible for any feasible gear size.