How to Choose the Right Gearbox with Electric Motor for Your Equipment?

Picking the right gearbox to pair with your electric motor can feel like a puzzle. Get it wrong, and your equipment could end up underpowered, overworked, or flat-out dead in the water. You want your machine running smoothly, efficiently, and for as long as possible, right? So how do you choose the right gearbox for your setup? Let’s break it down.


Before diving into technical specs, start by figuring out what kind of load your motor will be dealing with. The load type can vary widely depending on the application, and it will directly affect the size and strength of the gearbox you need.

Here are the most common load types:

  • Constant Load: Think of a conveyor belt in a factory, running at a steady pace all day long. The load is fairly predictable, with no huge spikes in stress.
  • Shock Load: Now imagine a forging machine or a crane that experiences big, sudden jolts of force. These machines need gearboxes built to handle those shocks, which means higher strength and durability.

When the load is constant and steady, you don’t need to go overboard with a super-heavy-duty gearbox. But for intermittent or shock loads, you’ll need a gearbox with a higher service factor to handle the extra stress.


The service factor is a critical number that helps you choose a gearbox with the right amount of cushion for your operating conditions. It’s basically a safety margin that takes into account things like the operating hours, load type, and even the environment your equipment is in.

motor for gearbox

Here’s a quick guide to service factors based on load conditions:

  • Light Load: For steady, light operations like conveyors, you can stick with a service factor of 1.0 to 1.25. Your gearbox won’t face major challenges, so this is all you need.
  • Moderate Load: Machines that start and stop a lot, like elevators, need a bit more room for error. A service factor of 1.25 to 1.5 will ensure the gearbox can handle the on-and-off load without breaking down.
  • Heavy Load: For systems that run in tough environments or face frequent shocks, like a crusher on a construction site, opt for a service factor of 1.5 to 1.75. This will give the gearbox the extra strength it needs to handle the stress.
  • Extreme Shock Load: If your equipment sees huge shocks, like in forging machines or oil drilling rigs, you’ll want the highest service factor possible—1.75 to 2.0 or higher.

Higher service factors mean your gearbox is built to last under more stressful conditions. Always consider the worst-case scenario for your equipment and go from there.


Now that you’ve got the load type and service factor figured out, it's time to calculate the output torque of the gearbox. This is where we get a bit technical, but don’t worry, it’s simpler than it sounds.

You can calculate the output torque using this formula:

[
T_{out} = \frac{9550 \times P_{motor}}{n}
]

Where:

  • (T_{out}) = Output torque in Nm (Newton meters)
  • (P_{motor}) = Motor power in kW
  • (n) = Output speed in rpm (revolutions per minute)

Once you have the output torque, compare it with the rated torque of the gearbox. Always make sure the rated torque of the gearbox is greater than or equal to the calculated output torque. Also, don’t forget to apply the service factor to add that extra layer of safety.


Why is this important? If your gearbox can’t produce enough torque, your motor will struggle to do its job, leading to overheating, wear, and premature failure. Nobody wants that.


Another key spec to figure out is the gear ratio. This is the ratio between the speed of the motor and the speed of the gearbox’s output shaft. It tells you how fast your equipment will operate once everything is connected.

You can calculate the gear ratio using the formula:

[
i = \frac{n_{motor}}{n_{out}}
]

Where:

  • (n_{motor}) = Motor’s rated speed (usually 1440 rpm or 2880 rpm)
  • (n_{out}) = Desired output speed

The gear ratio should help you achieve the desired speed for your equipment while ensuring the motor's power and torque are properly matched.

motor and gearbox

Tip: The right gear ratio makes sure your equipment runs at the correct speed without overloading the motor.


Once you’ve worked out the necessary torque and gear ratio, the next step is to cross-check the specs with the gearbox manufacturer’s catalog. You’ll need to make sure the model you choose meets all the requirements for your application, including torque, speed, and, of course, service factor.

Also, take a look at the environmental conditions. If your equipment is operating in harsh conditions—like extreme heat, cold, or high humidity—you may need a special gearbox or lubricants to handle these elements.


  • Starting Frequency: If your machine starts and stops frequently, you may need to adjust the service factor to account for the extra stress.
  • Temperature Effects: Extreme temperatures can impact both the motor and the gearbox. Make sure the gearbox you select can handle the environment, or be prepared to use special lubricants to compensate.
  • Maintenance: Some gearboxes are easier to maintain than others. If your equipment runs 24/7, make sure the gearbox can be serviced without long downtimes.
motor and gearbox

By following these steps, you can confidently choose the right gearbox to pair with your electric motor, ensuring your equipment runs smoothly and lasts a long time. From understanding load types to calculating output torque and choosing the right service factor, every decision plays a big role in the system’s efficiency and longevity.

When in doubt, it’s always smart to consult with a professional or reach out to the gearbox manufacturer for more detailed recommendations.

And if you’re in the market for a high-quality, reliable electric motor or gearbox, DONGCHUN motors has got your back! We offer top-tier, customizable motors perfect for any industrial application. Get in touch with us today for expert advice and the best motor solutions for your business.

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