How Do Planet Gears Work?

[IrisLab]

I have a question about how a planet gear system works. With a planet gear, suppose you have a DC motor connected to the planets. You are driving the planets with a constant torque Tp and angular velocity wp by applying a constant voltage v (or fixed width PWM).

Does the gear system split the torque between the sun and the ring such that Ts = Tp/N goes to the sun and Tr = Tp(1 - 1/N) goes to the ring? I'm using N to represent the gearing ratio between the sun and the planets and N>=1.

What about the angular velocity? Do these sum such that wp = ws + wr where ws is the angular velocity of the sun and wr is the angular velocity of the ring?

I guess my larger question is...what are the ratio relationships with gear turns for torque and angular velocity?

[Warren Boudreau]

From what I remember from planetary gear systems, one of the gear sets (sun, planets, or ring) must be fixed to ground. There is an exception to this that I will explain shortly. Anyway, depending on which gear set you ground, your gear ratio equation changes. I think you can figure that out from the looks of you post.

You can't have two outputs from the planetary set, which seemed to be what you were trying to do. You can have two inputs and that is the exception that I mentioned earlier. One of the teams last year figured out how to drive the ring and the sun (I think) with two different motors to get a constantly variable gear ratio. The CVT I think they called it. And I apologize to anyone who reads this and finds that some of the details about the CVT are distorted. It's been a rough summer and I don't remember too good sometimes.

Anyway, I hope this diatribe helps. Good Luck.

[JVN]

Originally Posted by Warren Boudreau

One of the teams last year figured out how to drive the ring and the sun (I think) with two different motors to get a constantly variable gear ratio. The CVT I think they called it. And I apologize to anyone who reads this and finds that some of the details about the CVT are distorted. It's been a rough summer and I don't remember too good sometimes.

I don't know much about planetary gears, but I do know about the "CVT" you were refferring to.

It was called the CCT - "Crazy Chicken Transmission", designed by Paul Copioli, from Team 217 - The Thunderchickens.
You can find a copy of the design, and the theory behind it here:
http://www.thunderchickens.org/downloads/cct_2002.zip

John

[Adam Y.]

Howstuffworks

[Matt Adams]

Here's a link showing planetary gear sets, along with a nice visual so you can get a better grasp on how they actually work. Very nicely done.

http://auto.howstuffworks.com/automa...nsmission2.htm

Matt

[IrisLab]

Originally Posted by JVN

It was called the CCT - "Crazy Chicken Transmission", designed by Paul Copioli, from Team 217 - The Thunderchickens.
John

This design is interesting. How well did it preform? It's very very similar to the Toyota Prius ECVT as near as I can tell. I'm not an expert in drives---not even close. I recently read an article about the Prius and how it uses a plantary gear system with an additional motor to achieve a CVT.

I noticed that the documents you listed noted that a Patent application was pending. I'd take a look at the Prius system. Maybe Toyota owes the Thunder Chickes team some big dollars! That could finance a healthy FIRST team!

The major difference that I see (and again I'm not an expert) is that Toyota uses a generator in the same way the CCT uses an extra DC motor to control drive speed and distribute torque. In the CCT the extra motor seems to have significant loss (in terms of efficiency) through the second motor. In the Prius, the generator attempts ot recover this power and feeds it back into the batteries.

Also, another diffence is that Prius uses an internal combustion engine as the main drive motor. Can we have a V-8 on a FIRST robot? :-)

Anyway, thanks for all the input. AND THE CCT IS WAY COOL! Thanks!

[matt111]

we are building a continously varible torque, velocity, steering transmission (cvt vst )
but dont ask me how it works...im just the cad dude

btw gears=not fun to model therefore use circles