gearmotor sizing

Selecting and Sizing Geared Motors

In this post, I’ll describe the process I use for sizing gearboxes and geared motors.

 

To make the selection, I am using KEB’s software sizing program called KEB-DRIVE.  KEB-DRIVE is free and easy to use.  If interested to follow along, you can download a copy of the software.

 

gearmotor sizing

 

 

 

1.  Consider the application requirements

Before you begin selecting a geared motor, you first need to consider and know the application requirements.  This is not a comprehensive list but gives a general idea of the common considerations.

 

Torque & Speed

  • What torque and speed are required at the output of the gearing?
  • What does the typical torque profile look like?
  • Is the loading more or less steady – or will the gearing experience shock loading?
  • What electrical power do I have (three phase, 50 or 60Hz, Voltage)?

 

Duty

  • What is the duty of the application?
  • If I need more motor overload – can I rate for a reduced duty like S2 or S3?

 

Control

  • Does the application require position, torque or speed control?
  • Will the motor be run across the line or with a VFD?
  • Will the motor hold the load at 0 speed indefinitely (e.g. hoisting application)?
  • Does the motor need a spring-set brake on it?
  • Does it need a feedback device like an encoder?

 

Mounting

  • How will the gearmotor be mounted to the machine  – foot mounted, shaft mounted, flange mounted?
  • Are there space constraints?
  • Does the output axis need to be inline or at a right angle
Parallel offset gearmotor hoist

This hoist uses an offset output which allows for the drum to be compactly installed.

 

Environment

  • What environment is the gearmotor going into (e.g. caustic washdown, saltwater, sensitivity to noise, etc.)?
  • What are the ambient temperature ranges during operation?
  • Does it require special ingress protection (washdown, outdoors, etc.)?
  • Is this a food processing application that will require food grade lubricants and grease?

 

 

 

2. Select the correct gear technology for the application

 

Configurations in KEB-Drive start at the top left.  On the left, you’ll see drop-downs to select different gear types and sizes.

gearmotor selection software

Start by selecting the gear type and size

 

KEB offers 4 main types of gearing:

 

Table 1
4 Types of KEB Gearing

“Style” Gear Type Output Efficiency (%)
G Helical Inline 94-96%
F Helical Parallel Offset 94-96%
S Helical-Worm Right Angle 50-90%
K Helical-Bevel Right Angle 94-96%

 

Helical-Worm and Helical-Bevel will provide right angle outputs. Helical-worm can be cost advantageous for larger reduction ratios.  Helical-bevel has the advantage of better efficiency, which can possibly equate to a smaller motor.

 

There is also an option available to leave off the gearing if are just interested in selecting a servo or induction motor.

 

vector induction motor encoder

KEB-DRIVE also allows standalone motor selection

 

 

 

3.  Motor Selection (Size, voltage, frequency)

 

Working to the right, I then select the size of the motor I want. Options for both Induction motors and AC Servo motors are listed.  Here is a comparison of the advantages between servo and induction motors.

gearmotor motor winding

Next, select the motor size and winding

 

There is a tab that allows you to select the stator winding information – specifically, the rated voltage and frequency.  KEB has the ability to offer special windings outside of what is listed.  Last year I worked on a 380V/60Hz installation in South Korea – who knew!

ie3-gearmotor-winding

Different IE3 windings are available for the Global market

 

Larger motors will provide more torque.  As you increase the motor size, you’ll see the torque information is updated in torque/speed drop-down.

 

 

 

4. Adjust the Torque/Speed selection

 

Is it a speed reducer?  Or a torque Increaser?  It’s both – higher gear ratios will provide lower output speeds and higher torques.  Use the drop down to see all the different possible configurations with the selected gearbox/motor combo.

 

There is a limit to the options that KEB-Drive will show.  Only options with a service factor of 1.0 or greater are displayed.

gearmotor torque speed ratios

Adjusting the ratio affects the output torque and speed

 

Note: If you have selected a motor winding that is rated for both 50 and 60Hz, you will see two values listed for the speed and torque.  The 50Hz rating will be reflected with the slower rpm output.

 

 

5.  What is the gearing Service Factor and why is it important?

The gearing service factor (SF) is the ratio between the:

gearing sf equation

 

In other words, Service Factor provides a relative comparison to how much capacity the gears have in the current configuration.

 

A SF of 1.0 means the gears will have a nominal output torque equal to that of their rating.  Selecting a motor/gear configuration with a SF of less than 1.0 is not advised.  This means the gears will be undersized when operated at the nominal point.  This could also indicate that the motor selected is too large.

 

Sometimes, the application is very difficult with regards to Duty, Shock loading, Temperature, etc. (look at step 1 – application requirements).  In this case, it is advisable to select a very high SF which compensates for the factors that will stress, wear, and possibly damage the gearing.

 

Manufacturers typically provide a table of typical applications.  Many also list a multiplication factor based on duty.  It is advised that difficult applications like a Rock Crusher have a SF in the 3.0 range or higher.  Relatively easy applications like fans with light duty might have a SF closer to 1.0.  It often becomes a trade-off between safety factor and cost.

 

At this point, if the selection is not able to meet the required torque, speed, and SF of the application, you’ll need to return to step 2 and select a different gear and motor combination.  Or conversely, if the motor or gear appear to be oversized, then you can return to step 2 in order to optimize.

 

 

6.  Select gearmotor options (mounting style)

 

This section allows a user to select how the geared motor will be mounted.  The flexibility of mounting is one reason that the KEB integral gearmotor solution has been so popular.  Users can select a unit with an output shaft.  Or a shaft mounted unit with a hollow bore.  Mounting feet and mounting flanges can also be selected.

 

F series gearbox

Hollow shaft gearmotors avoid using an intermediate coupling

 

For shaft mount applications, a nice option is a shrink disk mounting.  KEB’s shrink disc mounting provides a zero backlash connection between the gearbox and machine shaft.   Assembly and disassembly are very easy.

 

torq loc gearmotor

Shrink Disk mounting makes shaft mount assembly easy

 

To go along with the flexibility-theme, users can select either English or Metric units on the shaft/bores.  If you don’t see the exact option you want in the configurator, then I suggest contacting a KEB engineer to explore what is possible.  We are able to offer a lot of customer flange and bore designs if the customer wants.

 

This section also includes the lubrication used in the gearbox.  A number of different lubricants are possible depending on the application requirements.  Consult the KEB gearmotor manual but the temperature ranges for the lubricants is listed.  For food and packaging applications, a USDA food-grade lubricant is available.

 

Below that is a list of checkboxes that can be selected.  Gearing options like low backlash and protection covers are possible.

 

 

7.  Choose the motor options

This is where a user selects the motor options.  Options like a motor on the brake.  Or, the type of encoder for closed loop applications.  Even the type of motor fan can be selected here.

encoder-feedback-integral-gearmotor

KEB offers a variety of incremental and absolute encoder options

 

8.  General options

Next, the general options can be defined.  These are special requirements that can be easily selected in the configurator.  This includes a second nameplate, condensation drain hole, etc,   The conduit box orientation and the fitting location are also defined here.

 

Finally, the paint treatment can be selected here.  The number of applications and thickness of paint is defined.  Consult the KEB gearmotor catalog for the specifications.  Added protection is possible with the P1, P2, or P3 options. These would be good options to consider for washdown, outdoor, and maritime gearmotor applications.

IP65 gear motor used in marine application

IP65 gear motor used in marine application

 

The paint color is also defined here.  Gray and black are most commonly requested so they are standard options.  But we can paint to whatever color the customer specifies.  In the case of a special, contact KEB.

 

9.  Gather 3D models and dimensional drawings

The last option is the mounting position of the gearmotor.  This is important as it determines the oil fill level of the gearmotor and venting.

 

At this point, the user can explore additional tabs in KEB-DRIVE in order to get more information.  Of note, the customer can get extra motor information including the efficiency values, nominal torque, and inertia values.

motor inertia values

An exported summary includes detailed info like motor rotor inertia

 

The Dimensions tab includes a drawing with critical dimensions and 3D .step models.

geared motor 3D models

3D and Dimensional drawing outputs

 

 

Conclusion

KEB-Drive is a useful tool because it is easy to use and selections can be made very quickly.  However, please note that these are only the commonly requested features.  There are many more possibilities KEB can offer like absolute or safety encoders, quiet brakes for theatre or elevator applications, custom flanges, etc.

 

If you have specific needs feel free to consult with a KEB gearmotor engineer and we’d be happy to help with your application.

 

Contact Us

 

Related posts

VIDEO KEB Gear motors: German Engineered. American Assembled

Parallel offset gearmotor hoist

Theatre Gearmotors for Hoists and Winches

Helical Bevel Gearmotors

IE3 gearmotor winding

IP65 Washdown Integral Gearmotors

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