# Planetary Gear Design: Sun/Pinion Teeth Ratio 4:1

• zain1
In summary, it is possible to have the number of teeth of the sun gear and pinion will be same if the ratio is 4:1. However, if you take 15 teeth for the sun gear then the number of teeth on planet is also 15 with 45 on ring, which does not give the desired ratio of 4:1.
zain1
Hello
I want to ask that is it possible to have the number of teeth of sun gear and pinion will be same?

As In my case the ratio is 4:1...outer ring is fixed and sun gear is the input. I want to use three planets.
and if I take 14,16,17 for the sun gear then the condition of (Z1 +Z3)/number of planets should be integer.
but if i take 15 for the sun gear then the number of teeth on planet is also 15 with 45 on ring...

I want to ask is it right to take 15 teeth for both sun and planet and 45 for ring to get the ratio of 4:1?

Sun, Ns = 15; Carrier, Nc = 15; Ring, Nr = 45;
With the ring gear fixed, the gear ratio will be 1 + ( Nr / Ns ).
That will give a ratio of 4.000

The problem with such similar tooth counts, with common factors, is that there will be no hunting tooth. A blemish on one tooth of the sun gear will transfer every time to the same tooth on each of the planets. Those will always be met by the same three teeth on the ring gear. It would wear more evenly if the number of number of teeth were mutually prime.

To get a hunting tooth, look at a ratio close to the optimum. Instead of designing for a ratio of 4.000, look for something close to say 4.1

So long as Nr = Ns + 2·Nc it will work out. There is no real problem with planets that are unevenly placed around the carrier. It is not necessary to move a gear centre by more than half a tooth pitch to allow for any tooth count.

The required ratio is 4.1 = 1 + Nr / Ns
So we need to find two integers Nr / Ns that have a ratio close to 3.1
There are many to choose from with a hunting tooth.
If Ns = 12 then Nr = 37.2 near even is 38. Nc will be ( 38 - 12 ) / 2 = 13. Ratio = 4.166
If Ns = 13 then Nr = 40.3 near odd is 41. Nc will be ( 41 - 13 ) / 2 = 14. Ratio = 4.154
If Ns = 14 then Nr = 43.4 near even is 44. Nc will be ( 44 - 14 ) / 2 = 15. Ratio = 4.143
If Ns = 15 then Nr = 46.5 near odd is 47. Nc will be ( 47 - 15 ) / 2 = 16. Ratio = 4.133
If Ns = 16 then Nr = 49.6 near even is 50. Nc will be ( 50 - 16 ) / 2 = 17. Ratio = 4.125
If Ns = 17 then Nr = 52.7 near odd is 53. Nc will be ( 53 - 17 ) / 2 = 18. Ratio = 4.118
If Ns = 18 then Nr = 55.8 near even is 56. Nc will be ( 56 - 18 ) / 2 = 19. Ratio = 4.111
If Ns = 19 then Nr = 58.9 near odd is 59. Nc will be ( 59 - 19 ) / 2 = 20. Ratio = 4.105
If Ns = 20 then Nr = 62.0 near even is 62. Nc will be ( 62 - 20 ) / 2 = 21. Ratio = 4.100

Last edited:
Lnewqban
Tom.G and Baluncore

## 1. What is a planetary gear design?

A planetary gear design is a type of gear system that consists of a central gear, called the sun gear, surrounded by multiple outer gears, called planetary gears, and an outer ring gear. This arrangement allows for different gear ratios and torque distribution.

## 2. What is the sun/pinion teeth ratio in a planetary gear design?

The sun/pinion teeth ratio refers to the number of teeth on the sun gear compared to the number of teeth on the pinion gear. In a 4:1 ratio, the sun gear has four times as many teeth as the pinion gear.

## 3. How does the sun/pinion teeth ratio affect the gear system?

The sun/pinion teeth ratio affects the gear system in two main ways. First, it determines the gear ratio, or the ratio of the input speed to the output speed. In a 4:1 ratio, the output speed will be one-fourth of the input speed. Second, it affects the torque distribution, with a higher ratio resulting in a higher torque output.

## 4. What are the advantages of using a 4:1 sun/pinion teeth ratio in a planetary gear design?

Using a 4:1 sun/pinion teeth ratio in a planetary gear design offers several advantages. It allows for a high gear ratio and torque output, making it suitable for applications that require high power transfer. It also results in a compact design, making it ideal for use in tight spaces.

## 5. Are there any limitations to using a 4:1 sun/pinion teeth ratio in a planetary gear design?

While a 4:1 sun/pinion teeth ratio has many advantages, it also has some limitations. It may not be suitable for applications that require precise speed control, as the gear ratio cannot be adjusted. Additionally, the high torque output may result in increased wear and tear on the gears, requiring more frequent maintenance.

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