PLANETARY GEAR 1

[ricec]

Im trying to put together a planetary gear, i have a 14 teeth sun and 3 planetary gears (22 teeth), for the outer gear can somebody tell me how to calculate the no. of teeth and the ratio on the whole system. The gear is a dp 3

 

[carburized]

Generally for a true planetary, you need twice the no. of teeth in plane plus sun teeth equals ring teeth. In you case it will be 2*22+14=58 teeth in ring gear. Ratio is 1+Nr/Ns=1+58/14=1+4.143=5.143
Hope this helps.

Ravi

http://www.gearsandbearings.com

 

[asong]

Normally, the sun gear is design at positive profile shift coefficency.
to verify the teeth no is correct, you also need the following equation
(teeth in ring gear+teeth in sun gear)/no of planet gear=interger.

 

[ricec]

thanks for the formulas, it really helped me......i have another question....what is the difference in using 3 or 4
planet gears, is this just a matter of the power to be applied and use?????

 

[Philrock]

Asong is right about positive profile shift - especially for the small number of teeth in your pinion. If your pressure angle is 20 degrees and you have insufficient positive profile shift, the pinion will be undercut. If you have positive profile shift in a gear and its mate has equal but opposite (i.e. negative) profile shift, the center distance is the same as if both gears had no profile shift. Otherwise, center distance calculation is complex, requiring the use of the inverse involute function. Calculations can be found in Dudley's Gear Handbook. If the sun and/or planets have profile shift, there's a good chance the ring will need profile shift, as well.

Are the sun and planet gears already made? Do you have complete specifications for them?

3dp is a fairly hefty gear - what is it for?

http://www.baymachinedesign.com

 

[ricec]

Philrock......i do have the planet and sun gears, they are dp 3 and 14 1/2 degrees, i have calculated the center distance to be 6" between sun and planet gear.Im trying to build a reduction gear for a winch.

 

[paulliu]

The planetary gear drive with four planets will
transfer more power/torque than that using three
planets.

There are many questions and answers in gear engineering.

 

[Philrock]

Four planets will transfer more power than three if you have a way to assure good power sharing among the planets. If you use three planets and let the sun float radially, you are assured of very good power sharing among the planets.

Ricec, please post all you know about the gears you have:
outside diameters, root diameters, diameters over pins, profile shift, helix angle, etc.

What happens when you put the gears you have in mesh and check the center distance?

 

[diamondjim]

I would assume your pinion is heavily undercut
and would question the contact ratio for the
14/22 tooth combination. The 14.5 pressure angle
only ascerbates the situation as far as undercutting
and loss of tooth contact ratio. I assume these
are full depth teeth.

 

[asong]

If you design this device as new, I suggest you have the teeth number arranged this way:
z1+2*z2+1=z3
(z1+z3)/n=integer this equation I have mentioned above
z1 number of teeth of sun gear,
z2 number of teeth of planet gear,
z3 number of teeth of ring gear,
n number of planet gears, placed in equal angle.
The first equation seems not right, but that gives sun gear room for positive profile shift coefficency.
14.5 PA, that doesn't make sense for winch, if that is only to avoid undercut of sun gear, the designer didn't think of the sun gear much.

 

[asong]

The following is my suggestion about this gear set, use 22 teeth standard planet gears only, to make sun and ring gear as new.
data are in metric:
sun pinion z1=13 x=+0.593
ring gear z3=59 x=-0.373
center distance a=152.4
you can set the planet gears in 3 or 4, both are ok. but you need a carieer to keep them in place.