# Thread: Planetary gear speed reducer design

1. ## Planetary gear speed reducer design

Hello,

I have to design a series planetary gear speed reducer.
I have to ask first that what is SERIES planetary gear? Can anyone give some detail about this.

I have to design a gearbox with three stages with a motor power of 45 KW. Input speed of Motor is 2800 rpm, Max outer dia of gearbox is 100 mm. the gear ratio is 4:1 which is same in all three stages. I am doing this for the first time so please anyone can tell me in detail about how I can proceed....
Regards,
Zain

2. Welcome to Engineers Edeg Zain.

First, see: http://www.engineeringmotion.com/vid...rive-animation

I think you need to seek out an organizational engineer or designer whom is experienced in Planetary Gear design and ask for guidance. Designing a gear system is not trivial and it is easy to spend lots of time and money learning on your own.

3. Hi Zain,

Is this homework or a real project?

First off, I would question the possibility of this project with the constraints you have defined. You say 45KW (60HP) and 100mm (3.9") outside diameter of the gearbox. At a guess, the input shaft for 60HP would be about 1.5" diameter and that alone is 38mm. At 450lbs-ft torque, the output shaft is probably going to be 50-percent larger than that. It does not leave you much for the outer casing, outer-gear, inner-gear and planetary gears per set. I do not see this happening for you in 100mm.

A "series" gear set is where you have multiple planetary sets on the same shaft center-line. The overall ratio would be 4:1 but each gear set would be a ratio of 4 / 3 stages = 1.33-recurring, per set. Given the "recurring," the output will not be exactly 4:1.

You appear to be working this project from the wrong end. I agree with Kelly, seeks some very experienced and competent advice on this. It will be money saved in the long run.

Dave
Generally, I will not give you the answer to your question, but I *will* guide you into discovering how to solve this yourself.

4. Some places to look for design basics...
BREVINI
GRAHAM GEAR SYSTEMS
REXNORD

5. Hello,
Thanks for the replies,
This gearbox is basically for an oil rig. which have limitations of size. the gearbox is of 3 stages because of this small size.
the gear ratio is 4:1 for all three stages that means I have to keep the gears of same size in all three stages......... This is because of the small size to divide the forces and torques

6. Originally Posted by zain
...to divide the forces and torques
45KW at 2800rpm = 113-lb-ft of torque
45KW at 700rpm (4:1) = 452-lb-ft of torque

Good luck with that project.

Dave
Generally, I will not give you the answer to your question, but I *will* guide you into discovering how to solve this yourself.

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