Engineering Notes by Oriental Motor

Gearhead Selection for Brushless Motors

[fa icon="calendar"] Originally posted on Jun 27, 2024 5:48:20 PM
Last updated on July 3, 2024 / by Johann Tang

Johann Tang

Gearhead Selection for Brushless Motors
14:03

Gearheads play a crucial role in motor performance optimization. Each type of gear offers its own features and characteristics, and the gear ratio alters a motor's output torque and speed. By carefully selecting the optimal gear type and ratio, engineers can fine-tune motor performance to align precisely with the application requirements.

A motor becomes a gear motor when a gearhead is assembled with a motor.  The motor case contains the windings, the rotor, the stator, and a machined pinion shaft that would mesh with the gears inside a gearhead.  The gearhead case consists of bearings and gears that can multiply a motor's torque but also reduce its speed by the same ratio.  The gearhead also has an output shaft where the load attaches to.

Similar to a belt-and-pulley mechanism, where one pulley runs slower than the other due to the difference in the two pulley diameters, a gearhead's output shaft runs slower than the motor pinion shaft by the factor of its gear ratio. The advantage is that the gearhead is more rigid and can house a series of gears in a much smaller footprint than a belt-and-pulley mechanism.

In this article, I'll cover the types of gearheads offered for brushless gear motors and how to select one.

 

Topics covered:

I. About Brushless Motors
II. Gear Selection
III. Summary
 
I.  About Brushless Motors
 
First, here's a little background about brushless motors.  A brushless motor, or a brushless DC motor, is a type of closed-loop DC motor that is continuous duty rated and commutates its windings with a dedicated driver.  Due to their compact size, light weight, speed regulation, and high efficiency, brushless motors are ideal as drive solutions for variable speed material handling applications, such as conveyors or an AGV/AMR.  The lack of holding torque makes them less than ideal for positioning applications.
 

High Speed Stability

With closed-loop speed regulation by hall-effector sensors or encoder, the dedicated driver for a brushless motor constantly monitors the motor speed and changes the applied voltage to adjust the actual speed of the motor closer to the set speed.  Even with load fluctuations, the motor speed will only fluctuate ±0.2% at most (±0.05% with encoder equipped brushless motors).  
 
For applications such as pinch belt conveyors where two belt speeds have to be synchronized, brushless motors present a more reliable speed control solution than VFD/inverter-controlled AC induction motors, which run open-loop.
 
High speed stability from brushless motors
 

Space Saving

The compact yet powerful brushless DC motor incorporates permanent magnets in the rotor. Compared with an AC induction motor with a frame size of 3.54 in. (90 mm), a brushless DC motor of the same specifications is 62% shorter.  With a much shorter length, a brushless motor is also 62% lighter than an AC induction motor of the same frame size. 

The compact motor structure is helpful when downsizing equipment or reducing the load on an AGV/AMR.

 
Compact size of brushless motors
 

Energy Saving

Brushless DC (BLDC) motors, which incorporate permanent magnets in the rotor, generate little secondary loss from the rotor.  Compared to AC induction motors, brushless motors can have up to 66% less loss.   At an output power of 1/6 HP (90 W), for example, the power consumption of the BMU Series brushless DC motor is approximately 26% less than that of a VFD/inverter-controlled AC motor.  In the same frame size, a brushless motor can output 1.3 times more power than an AC induction motor.

Brushless motors consume much less power when compared to AC induction motors due to their design.
 
Energy savings of brushless motors
 
 
Since brushless motors can run at 3,000 to 4,000 RPM, the gearheads paired with these motors must be quiet even at high speeds, and they also must have high permissible torque and long life to make the most of the high performance motor's characteristics.  Our lineup of gearheads for brushless motors includes several parallel shaft gearheads (GFS, JV, JB), parallel shaft gearheads with centered output shaft (CS), hollow shaft right-angle gearheads (JH), and hollow shaft flat gearheads (FR).
 
By attaching a gearhead to a motor, you can:
  • Increase torque
  • Reduce speed
  • Reduce speed fluctuations
  • Reduce vibrations
  • Reduce overrun
  • Increase axial load
  • Increase radial load
Relationship between gear ratio and torque

 

FYI
When selecting gearheads, pay attention to the rotation direction of the gearhead shaft.  Some gearheads reverse the shaft rotation with certain gear ratios.

 

II.  Gear Selection
 
What kind of gearheads are offered with brushless gear motors?  I'm glad that you asked.  Here's the standard gearhead lineup for our brushless gear motors.  We split the lineup into 2 categories: long life and high torque.
 
👍 For Long Life:
Pararallel Shaft Gearhead (GFV gear type) Up to 619 lb-in (70 Nm) | 10,000 hours rated life 

IP66 Parallel Shaft Gear Motor

 

IP67 Rated Brushless DC Motors

 

H1 Food-Grade Grease-Compatible Gear Motors

GFV gear type parallel shaft gearheads are compact and are the most common type of gearhead offered for brushless motors.   They use a combination of helical and spur gears.

These gearheads are offered for brushless motors ranging from 30 W to 400 W and can reach a permissible torque of 620 lb-in or 70 Nm.  Gear ratios are offered from 5:1 to 200:1.  They have a long life rating of 10,000 hours.

High strength and low noise characteristics are achieved through improved case rigidity, carburized and hardened gears, and more precise assembly technology.  The high permissible torque is 2 ~ 3 times that of a gearhead for an AC motor with the same frame size.  With the gearhead's boss and machined mounting surface, the installation accuracy has also been greatly improved.

This gearhead is rated for long life and uses a special bearing and grease for high speed rotation.  A rated life of 10,000 hours is achieved.  Both IP66 and IP67 versions are offered, and an H1 food-grade grease option is available.

 

Availability: all product series

FR Hollow Shaft Flat Gearhead (GFS gear type) Up to 940 lb-in (106 Nm) | 10,000 hours rated life
Hollow Shaft Flat Gear Motor

FR hollow shaft flat gearheads provide high permissible torque axially without saturation even at high gear ratios.  The unique case design allows larger bearings and gears for higher strength.  Like a right-angle gearhead, they can also help save space and eliminate components such as couplings.

These gearheads are offered for brushless motors ranging from 30 W to 400 W and can reach a permissible torque of 940 lb-in or 107 Nm.  Gear ratios are offered from 5:1 to 200:1.  They have a long life rating of 10,000 hours.

 

Availability: all product series

CS Centered Shaft Gearhead (Spur) Up to 30 lb-in (3.38 Nm) | 10,000 hours rated life
CS geared brushless motor

Compared to the parallel shaft gearhead (GFV), the CS centered shaft spur gearhead offer higher permissible axial and radial load.  It can achieve 1.6 times more torque with the same frame size.  The centered output shaft helps simplify machine designs and installation.

These gearheads are currently offered for stepper motors and smaller brushless motors ranging from 30 to 50 W and can reach a permissible torque of 30 lb-in or 3.39 Nm.  Gear ratios are offered from 5:1 to 20:1 only.  They have a long life rating of 10,000 hours.

 

Availability: PKP Series, BLH Series

 

👍 For High Torque:

JV Gearhead (Flange Mount Type) Up to 3,814 lb-in (431 Nm) | 5,000 hours rated life
JV Gear Brushless DC Motor

JV type gearheads are rated for IP66 and offer superior mechanical strength.  They can be directly installed by using the flange surface. 

These gearheads are offered for brushless motors ranging from 200 W to 400 W and can reach a permissible torque of 3814 lb-in or 431 Nm.  2 gear ratios are offered: 300:1 and 450:1.  They have a long life rating of 5,000 hours.

 

Availability: BMU Series, BLE2 Series

JB Gearhead (Foot Mount Type) Up to 5,159 lb-in (583 Nm) | 5,000 hour rated life
Parallel Shaft (Foot Mount) Geared Brushless Motor

JB type gearheads are rated for IP44 and offer high rigidity and permissible torque.   Due to the built-in foot mounts, no external mounting bracket is necessary.

These gearheads are offered for brushless motors ranging from 200 W to 400 W and can reach a permissible torque of 5159 lb-in or 583 Nm.  Gear ratios are offered from 5:1 to 1200:1.  They have a long life rating of 5,000 hours.

 

Availability: BMU Series, BLE2 Series

JH Gearhead (Right-Angle Hypoid Type) Up to 1,575 lb-in (178 Nm) | 5,000 hours rated life
Right-Angle Hypoid Hollow Shaft IP66 Geared Motor

JH type gearheads offer high permissible axial load, high permissible radial load, and stainless steel hollow shaft in a right-angle orientation.  The hypoid gear it employs offers higher efficiency than other types of gears like worm gears.  Like any right-angle gearhead, use it to save space or eliminate components like a coupling.

These gearheads are offered for brushless motors ranging from 60 W to 400 W and can reach a permissible torque of 1575 lb-in or 178 Nm.  Gear ratios are offered from 5:1 to 200:1.  They have a long life rating of 5,000 hours.

 

Availability: BMU Series, BLE2 Series

 
As you can see above, there are many types of gearheads available for brushless gear motors.  How do you determine which one to use?  I'm glad you asked again.
 
First, determine if the gearhead + motor will satisfy your torque, load inertia, and speed range requirements.
 
There are many formulas to use to calculate the required torque.  The trick is knowing which one to apply.
 
Conveyor load torque calculation
 
For the belt conveyor example above, here's the formula used to calculate the required torque.
 
Formula for calculating load torque for conveyors, rack and pinion systems
 
Calculate your required torque and add an adequate safety factor.  Make sure this value is under the permissible torque specification of the motor + gearhead.
 
Next, add up all load inertia values of objects that are driven by the motor.  In a conveyor, you would calculate for the pulleys and the load being moved linearly.  Make sure the total inertia value value is within the permissible load inertia of the gearhead + motor.  The formula used to calculate load inertia depends on the mechanical setup.  Make sure to use the right formula to calculate your load inertia and provide adequate safety factor if necessary. 
 
Inertia of a Cylinder or Disc (as from the X or Y-axis)

Moment of Inertia Calculation - Cylinder

 

Example: Inertia of a Load in Linear Motion

Moment of Inertia Calculation for an Object in Linear Motion

 

Lastly, determine your required speed range and verify if it's within the capabilities of the motor + gearhead. 

 

FYI

Typically, the combined specifications for the gearmotor are already listed by the manufacturer, so all you have to do is verify the numbers.  However, if you purchased a motor and a gearhead from different manufacturers, then you'll have to do some calculations to determine the final output.

The torque at the gearhead output shaft is the motor torque multiplied by the gear ratio and gear efficiency:

Permissible Torque

TG = TM × i × η​​

T.G.​ = Gearhead Permissible Torque
T M = Motor torque
i = Gearhead reduction ratio
η = Gearhead transmission efficiency

The gearhead output shaft speed is the motor output shaft speed divided by the gear ratio.

Gearhead Output Shaft Speed Calculation

 

Second, check if the gearhead can handle your axial and radial loads.
 
Radial Load Axial Load of Gearhead
 
Refer to the specifications of the gearhead or gearmotor for the axial load (AKA: thrust load) and radial load (AKA: overhung load) specifications.  They should be in newtons or kilograms.  Your axial load and radial load should be under the max values.
 
For more information about motor sizing calculations and formulas, please refer to our motor sizing notes series or a conveyor sizing and selection example.
 
With the required torque, load inertia, speed range, axial load, and radial load, you now have the right information to select an optimal gearhead and gear ratio. Other things to consider include how high of an IP rating you need, how the gearhead fits into your design (right-angle shaft vs parallel shaft), and, of course, how much you can afford.  Sometimes, you can't have everything you want, so it's important to separate the must-haves from the nice-to-haves that might not be necessary for the application.
 
FYI Does gear backlash matter in conveyor applications?
No.  Backlash is not a major concern unless you're moving in both CW and CCW directions and need high stop accuracy.  For unidirectional applications where the motor is always rotating in one direction, such as a conveyor, the effect of backlash is minimized.

 

III. Summary
 
At last, here's a quick reference table that summarizes each type of gearhead offered for Oriental Motor's brushless gear motors.  FYI the permissible torque values below are based on 200 W (1/4 HP) gear motors and max gear ratios.
 
As always, our team is anxiously standing by to help with product selection and answer any questions.
 
Gearhead comparison chart for 200W (1/4HP) brushless motors
 
✽The rated life for 15 W is 5,000 hours.
The values for permissible radial load, permissible axial load, and permissible torque are for the following operating conditions. They will vary based on the combined motor output power and gearhead gear ratio.
· Output Power : 200 W (For CS geared motors, values are for 50 W models.)
· Motor Shaft Speed: 3000 r/min
· Gear Ratio : Maximum gear ratio for each gearhead (Example: For GFV gear, the gear ratio is 200)
 

Topics: Speed Control, BLDC Motors, Gearheads, Motion Control Basics

Johann Tang

Written by Johann Tang

Johann Tang is a Product Specialist at Oriental Motor USA Corp. Before joining the marketing team, he spent 15 years in sales, technical application support, and training of various types of fractional horsepower electric motors, gear motors, actuators, drivers, and controllers. If you have any questions, please feel free to use the live chat window, 1-800-GO-VEXTA (1-800-468-3982), or techsupport@orientalmotor.com, to reach our product support team. Johann can be reached via LinkedIn. Sorry, comments have been turned off.

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