0
$\begingroup$

I created the following planetary gear in FreeCAD. planetary gear

I calculated number of teeth using formula R = 2*P+S. In my case R = 75 P = 5 (there are 3 of them) S = 45.

Also all gear have the same pitch of 2.5 mm. However picture has huge gap. I can not figure out what could be wrong. Here is link to FreeCAD file link

$\endgroup$
1
  • $\begingroup$ what is the actual problem? ... what is your question? $\endgroup$
    – jsotola
    Nov 5, 2021 at 1:37

2 Answers 2

1
$\begingroup$

The following image explains where the formula $R=2P+S$ comes from.

enter image description here

Figure: Planetary gear with 4 planets (https://woodgears.ca/gear/planetary.html)

Although it has 4 planets the spacing will be the same with 2 or more planets. (Three is used for optimal balance and redundancy).

Essentially, the diameter of the Ring $d_R$ should be equal to the Diameter of the sun $d_S$ plus 2 diameters of the planets $d_p$. I.e. :

$$d_R = 2d_P+ d_S \tag{eq:1}$$

However for gears, the diameter of a gear ($d$) and the number of teeth ($z$) are proportional.

  • in the metric system usually the module m is used, $d= m\cdot z$
  • in the US system usually the Diametral Pitch (P) is used, $d= \frac{z}{P}$

In both cases, the equation 1 becomes:

$$z_R = 2z_P + z_S$$

So for $z_R=75$ and $z_S=5$, the correct number for the teeth of sun is $z_S = 75-2*5=65$

$\endgroup$
2
$\begingroup$

You are almost there. Except you need to use $2p=10. \\ not\ \ 2*3*p=30$

You use the number of the gears of one of the middle planetary gears no matter how many are there.

As you can see adding more P gears would not change the ratio, it probably reduces the stress on the gears.

Then you would have

  • R=75
  • S= 65
  • P= 5
$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.