×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*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.

Students Click Here

Question on a planetary gear system

Question on a planetary gear system

Question on a planetary gear system

(OP)
With very limited knowledge in the area I;ve been asked to reverse engineer a simple planetary gear system.

  The sun gear is the driver. The Annulis is fixed and the planet gears are the driven.

  I counted the number of teeth on each gear:
     Planet = 18 teeth.
     Sun = 11 teeth
     Annulis = 49 teeth.
  This seemed strange to me since I assumed the Annulis should equal twice planets plus the sun. I counted again and again and...

  Anyways. I would appreciate some help. What would be the most likely explanation for this. I have been working over the weekend on this and haven't been able to do any accurate measurements. It looks like the Sun gear has a different diametral pitch (13) than the planets and the annulis(14).

  Any help would be greatly appreciated. Thanks.    
 

RE: Question on a planetary gear system

Having an "odd" number of gear teeth also is used to make sure you dont get the exact same gear teeth mating each time.

If there were an imperfection on one tooth on one of the planets, and it kept hitting the same tooth on the ring gear, it could quickly cause a problem on that one ring gear tooth.  By having an odd number of teeth, any problem is spread out more evenly over all the ring gear's teeth, increasing the life of the gear set.

So in other words it may be completely on purpose.

RE: Question on a planetary gear system

Kevin,
Mike and fxlarry are both right.  The sun
probably has a 50 percent plus profile shift
to strengthen the teeth.  You really need
to know or determine the exact center distances
of the parts.  First the cd of the sun and planet
and then the cd of the planet and internal gear or
annulis.  By using 3 different near size pins
and checking the measurement over pins for the
sun and planet, you can determine the involute curve
with some certainty.  You could also check the
dimension under pins for the gear.
Would be glad to solve this with this information
submitted or given.  If you cannot measure the
dimension over pins, you can probably just use
depths from the od and check the chordal tooth
thicknesses at 3 different depths to determine
the involute curves.  I would imagine that the
a standard dp or module was used, but the pressure
angle is probably also one of the standards like
14.5 20 22.5 or 25.  Would be glad to help you
solve this in acad if you can furnish the center
distances and the od of the idler, sun, and id
of the internal ring gear.  You can call me at
noon eastern standard time at 330-562-4000
ext 238 if you wish.  How soon do you need a
specific answer?  This sound very much like a
job I was working on for someone up in Canada
about 12 years ago.  Home phone 330-678-0226
in the evenings. No charge for services.
Your original statement is correct in that in
most cases you can add twice the idler to the
sun to get the number of teeth in the annulis.

RE: Question on a planetary gear system

Kevin and all,
This 18 11 and 49 planetary system is
interesting in that the primes as
2 3 11 and seven.  Since the sun and annulis
have different primes, they cannot be
spaced at exactly 120 degrees apart.  Does
anyone know a formula of how to calculate
the exact angles that they would operate.
Normally the sun and annulis have common
primes and determine the number of planets.
I have not seen this addressed before.
Could the above use more than 3 planets to
have different starting points like fxlarry
pointed out.  I know it is convenient to use
primes to determine the planets, but is this
necessary?  This could probably be a new
question or post.

RE: Question on a planetary gear system

diamondjim,
post your e-mail. I have the formula.
gearguru

RE: Question on a planetary gear system

This planetary (11T sun, 18T pinion, 49T annulus) can have 3 or 4 or 5 or 6 equally spaced pinions.
gearguru

RE: Question on a planetary gear system

In my previous statement please correct:
3 or 4 pinons equally spaced. They also have enough space to be in an assembly. Theoretically 5 and 6 equally spaced could be inserted, but they had to be ofsetted axially, because there is not space between the pinons to accomodate them.
Also: If for some reason the pinions have to be located at a different angle, then they have to move 6.0 (or 12 0r 18...)degrees from the exact - (120 or 90 degree) location.
gearguru

RE: Question on a planetary gear system

gearguru,
My e-mail for is
J.Geisey@juno.com
I have been able by trial and error
rotate the pinions in acad and get
them in the right position but a formula
would be nice. When you say axially
I think you mean circumferentially about
the sun?  Axially means to me up and down
on the shaft.
Thanks in advance.

RE: Question on a planetary gear system

diamondjim,
I really meant axially. In this planetary there is no space to locate 5 or 6 pinions next to each other. If we want to use that many, they must be "behind each other", using wide sun and annulus.
gearguru

PS

Merry Christmas and a Happy New Year to all of you who read this messages!
   

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.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members! Already a Member? Login


Resources

White Paper - Strategies to Secure Connected Cars with Firewalls
White-hat hackers have demonstrated gaining remote access to dashboard functions and transmissions of connected vehicles. That makes a firewall a vital component of a multilayered approach to vehicle security as well as overall vehicle safety and reliability. Learn strategies to secure with firewalls. Download Now
White Paper - Model Based Engineering for Wire Harness Manufacturing
As complexity rises, current harness manufacturing methods are struggling to keep pace due to manual data exchanges and the inability to capture tribal knowledge. A model-based wire harness manufacturing engineering flow automates data exchange and captures tribal knowledge through design rules to help harness manufacturers improve harness quality and boost efficiency. Download Now
White Paper - What is Generative Design and Why Do You Need It?
Engineers are being asked to produce more sophisticated designs under a perfect storm of complexity, cost, and change management pressures. Generative design empowers automotive design teams to navigate this storm by employing automation, data re-use and synchronization, and framing design in the context of a full vehicle platform. Download Now
eBook - Simulation-Driven Design with SOLIDWORKS
Simulation-driven design can reduce the time and cost of product development. In this engineering.com eBook, we’ll explore how SOLIDWORKS users can access simulation-driven design through the SOLIDWORKS Simulation suite of analysis tools. Download Now

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:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close