×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Are you an
Engineering professional?
Join Eng-Tips Forums!
• Talk With Other Members
• Be Notified Of Responses
• Keyword Search
Favorite Forums
• Automated Signatures
• Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

#### Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

# Planetary gear train help

## Planetary gear train help

(OP)
Hi,
I will design a planetary gear train. The planet gear will be connected to a stirrer that applies approximately 100 Nm torque. The center distance between sun and planet must be apprx. 90mm. Planet gear must rotate at 100 rpm. Also carrier arm must rotate 1 time cw. as the planet gear rotates 3 or 5 times ccw. I need module and teeth number of gears. Thanks...

### RE: Planetary gear train help

have a look on my site for planetry configurations
http://uk.geocities.com/mikebull2001/green.html ; it won't give you sizes but you can get an idea of the relative diameters of the parts

### RE: Planetary gear train help

What kind of face width are you allowed?

### RE: Planetary gear train help

(OP)
Do you mean the type of gears by asking "kind of face"? if it is; they will be spur gears. Also i think i've found a start point. I took 3*pitch circle of planet equals 1*pitch circle of sun gear. Thus diameter ratio is 1/3. But i'm still not sure that will i take the pith circle of sun gear or pitch circle of annulus. Or may be i'm still thinking wrong completely. (Sorry for poor english)

### RE: Planetary gear train help

Caesarean,
what will be input in your planetary: probably sun, right?
What will be the output? Carrier or annulus? The overall (output/input) ratio is also what we should know. You are right - if the planet spins 3 times (around it's own center line!!) per 1 rotation of the sun, the pitch diameters of planet and sun (and also no. of teeth )must be in the 1/3 ratio.
diamondjim asked how wide the gears can be. It is necessary to know it for calculating the strength of gears.
Do not worry about language. You obviously did not select the place where you were born.
gearguru

### RE: Planetary gear train help

(OP)
Sun will be the input yes.. And the planet will be the output, annulus is fixed (sorry i must provide these info). When i take my pinion (planet) 18 teeth, sun 54 teeth, annulus 90 teeth the ratio is -0.6. I didn't give necessary info so you have misunderstood me. I will design the gears, so i must choose the material (also its yield str. tensile str. hardness etc.) then find the face width.
By the way i did some work: when i choose BS 826M40 (Y.S.=1020 MPa, T.S=1200 MPa and Hardness=400HB approx.) i found face width 55mm for surface fatique. Is there something strange. But unfortunately learned that i can't find BS 826M40 in Turkey. I must deal with some other steels.
One more thing: Which is more efficient; planet is pinion or sun is pinion. Thanks...

### RE: Planetary gear train help

OK: Sun is input;
annulus is fixed;
planets (=pinions) are carried by the carrier which is the otput.
How many pinions(planets) you have? There are restrictions if you want them equally spaced; but the no's of teeth which you have, give you 3, or 4, or 6 equally spaced planets. Calculate the stresses twice: for sun-planet and planet-annulus (which is usually les problem than the sun-planet). Divide the overall torque on the planets. To be safe, do not expect that all of them will be loaded exactly same. 55mm width is too big; recalculate it with more planets.
gearguru

### RE: Planetary gear train help

check the ratio, if the sun is the input, the annulus is fixed, then the carrier (output) will be rotating 0.375 as fast as the input -   ratio (90/54)+1) = 2.66:1

### RE: Planetary gear train help

(OP)
Ok. I think i will overcome the face problem. Lastly could you just say the needed teeth numbers for planet:100rpm, carrier:33 or 20 rpm, annulus:fixed. Then the corresponding rotation of sun?.. (Sun will be input but i must get these values as an output) By the way one planet will be used; does this create some balance problems or not.
Thank you very much to all who helped up to now.

#### Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

#### Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Close Box

# Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

• Talk To Other Members
• Notification Of Responses To Questions
• Favorite Forums One Click Access
• Keyword Search Of All Posts, And More...

Register now while it's still free!