# How can I design a gear train to meet specific torque and RPM requirements?

• OblongPea
In summary, the conversation discusses the design of a gear train for a lead screw that requires 140Nm of torque and a speed of 200RPM. The person is considering using spur gears but realizes that a gear ratio of 7:1 is needed, which exceeds the recommended maximum of 5:1. They then propose a design with four gears and question whether the number of teeth and diameter of the gears affect the torque and RPM. The expert recommends reading a book on practical gear design and suggests alternatives such as synchronous belt drives or buying a gear reducer. They also question if the project is a homework problem and suggest moving it to a different section.
OblongPea
TL;DR Summary
Request for help on gear train design
Hello, I'm after some advice/ clarification on some gear train design. This may just be a simple clarification

Requirements
I have a lead screw which needs to be supplied power by a Motor.
This Lead screw must have 140Nm Torque to raise and lower the load, and must turn at 200RPM.
The motors I am finding are providing about 20Nm of Input Torque at approximately 1400RPM. So I'll assume for this I will be using one of these.
I wish to use Spur Gears within the gear train.

I know that Spur Gears should have a maximum gear ratio of 5:1. Therefore using 2 gears (One from the Motor, One on the screw) isn't possible as this requires a ratio of 7:1.

I looked at many options, and using a set-up similar to the attached image is my conclusion, where there are 4 gears.

The issue I have is determining what gears, no. of teeth etc. in order to get the required Torque AND Rpm from the Motor.

My idea was to use a ratio of 3.5 from Gear 1 to 2 (n1, n2 on the diagram). Giving a Torque of 70Nm on the second gear, and 400 Rpm.

Then as gear 3 will have the same Rpm and Torque (I think??) as Gear 2 as its on the same shaft, I thought to use a ratio of 2 from Gear 3 to 4 to give me a Torque of 140Nm and 200 Rpm.

Is this correct? I am questioning whether the number of teeth and diameter of the gears affect the torque and Rpm in any way?

#### Attachments

• Gears.jpg
47.2 KB · Views: 168
Your sketch would work. There is a lot more to designing a gear reducer than just calculating numbers of gear teeth. Gear pitch diameters, gear tooth size, gear tooth form, shaft sizing, bearing sizing, housing design, lubrication, and much more all need to be calculated. A good book to read is Dudley's Handbook of Practical Gear Design: https://www.amazon.com/dp/1498753108/?tag=pfamazon01-20. If you read this book, you will understand why most engineers avoid designing their own gears if at all possible.

Are you sure that you need a gear drive? There are also synchronous belt drives available that work very well. One example is Gates Poly Chain GT belt drives. See this link to their catalog: https://www.gates.com/content/dam/g...y/catalogs/old-pc_carbon_manual17595_2011.pdf. They have the components to make a 7:1 reduction drive in a single stage.

If you need gears, the preferred method is to buy a gear reducer. There are many manufacturers of many different styles of gear reducers. A search will find them.

Or is this a homework problem? If so, it needs to be moved to the Homework Help - Engineering section.

berkeman, Dr.D and Lnewqban
Many thanks for your input here, I will read the book you mentioned as it seems to contain all the information I require. Looking through it briefly, I see why Engineers prefer to buy!

It's not necessarily a homework problem, just a small custom theoretical project I'm doing to upskill myself as I haven't had a lot of experience with gears.

berkeman

## 1. What is gear train design assistance?

Gear train design assistance is a service that helps engineers and designers in the process of designing and optimizing gear trains for various mechanical systems. It involves analyzing the system requirements, selecting appropriate gear types and sizes, and ensuring efficient and reliable operation of the gear train.

## 2. Why is gear train design important?

Gear trains are an essential component in many mechanical systems, such as automobiles, industrial machinery, and robotics. Proper gear train design ensures efficient power transmission, smooth operation, and longevity of the system. It also plays a crucial role in reducing noise, vibration, and wear and tear of the system.

## 3. What factors should be considered in gear train design?

Several factors should be considered in gear train design, including the desired speed and torque of the system, the type of power source, the available space for the gear train, the desired gear ratio, and the required precision of the system. Other factors may include the material and manufacturing process of the gears, lubrication, and environmental conditions.

## 4. How can gear train design assistance benefit a project?

Gear train design assistance can benefit a project in several ways. It can help optimize the gear train for maximum efficiency, reduce design and production time, and ensure the gear train meets the required specifications and standards. It can also provide valuable insights and recommendations for improving the performance and reliability of the gear train.

## 5. Can gear train design assistance be customized for specific applications?

Yes, gear train design assistance can be customized for specific applications. The service provider will work closely with the client to understand their unique requirements and tailor the design process accordingly. This may include using specific gear types, materials, or manufacturing processes to meet the specific needs of the application.

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