Which gearbox fits which motor?

The constantly growing motor product portfolio from igus also includes the right accessories. These include proximity switches, couplings and, of course, gearboxes. If the motor data sheet does not provide a solution for the required torque for your application, a gearbox in combination with stepper motors or EC/BLDC motors could be the solution.

Learn how to easily select and calculate the right gearbox for your electric motor in this article. There is also a side note on the function, design and installation of the gearbox. Finally, we provide a quick overview of the DC motors with pre-assembled worm, planetary, and spur gearboxes.

Industrial gearbox with shaft and flange connection.

The right gearbox for the stepper motor, or the EC/BLDC motor

MOT-AN-S-060-035-060-L-A-AAAA datasheet with dimension drawing, curve, and motor and general tables. — Example of a data sheet

Let's assume you need an electrical drive with a NEMA24 size. For your application, you need a torque of 30Nm and a speed of 10 revolutions per minute.

For the first step, you need the data sheet for the stepper motor (see example on the left). You can find this in the igus shop under "Downloads" for the relevant motor.

Let's move on to the second step: To do this, we need to briefly explain which gearboxes are available. These can also be found in the shop.

At the moment, several sizes are available, e.g. the motor gearbox with a flange of 60mm and 90mm. In our case, we refer to the 60mm flange, as we need a stepper motor NEMA24. On the product detail page, you will now find a drop-down menu with the different gear ratios that igus currently offers. To get more information, please download the data sheet.

Determine the correct reduction ratio

In the third step, look at the data sheet and the various versions of the reduction gearboxes. You can quickly estimate that the gearbox with a 10:1 reduction must be the right one here. Let's check:

The torque on the output side results from the rated torque of the motor multiplied by the gear ratio (rated torque motor x gear ratio = torque output side):

3.1Nm x 10 = 31Nm

Since gearbox losses occur, the efficiency is also taken into account. This is multiplied by the torque on the drive side (torque on the output side x efficiency = actual torque)

31Nm x 98% = 30.38Nm

The speed on the output side is now the speed of the motor divided by the reduction ratio (output speed = motor speed / reduction ratio):

100rpm ÷ 10 = 10rpm

The result

This means that the NEMA24 stepper motor with the 10i gearbox is the right one for us. We took the efficiency specified in the data sheet into account and also confirmed that we were below the rated output torque and would not exceed the emergency-stop torque. So our design fits.

If you are interested in an EC/BLDC motor, the procedure is exactly the same.

However, the path to our goal can easily be shortened with our tool "drylin motor expert", or DMX for short. In this tool, you can select the torque (0.01Nm to 44Nm), the speed (1rpm to 3,000rpm) and the duty cycle (1% to 100%). You will then be shown all possible variations with the utilisation.

Nevertheless, there are situations in which the matching motor with the correct gearbox is not displayed or the information is insufficient. One example is the inflexible installation space, which only fits one NEMA size. Here, the well-tried method is used: data sheet with the characteristic curve of the desired motor and calculating, as described in detail above.

Side note: Function, design and installation of a gearbox

The igus gearboxes can be used for all stepper motors and EC/BLDC motors with the correct screw dimensions. As a company, our requirements for the gearboxes are that they have a compact design and are capable of transmitting high torques. Therefore, all our gearboxes are planetary gearboxes. If you purchase the motor and gearbox from us as a combination, they will be pre-assembled for you at our factory.

Rear side of the NEMA 24 gearbox with marked components and mounting points.

How to assemble the gearbox

Pay attention to the screwing dimensions during assembly. In order not to choose the wrong gearbox for the relevant motor, the correct motor installation size is noted in the description of the planet gearboxes.

The two components are then joined with screws (see 1). Then you still have to connect the shaft of the motor to the gearbox (see 2). To do this, the cap on the side of the gearbox must be removed (see 3). Once this is done, the motor shaft is fixed to the gearbox by a screw on the gearbox input. The torque must be taken into account, which is different for each motor.

That's it! You've done it. To disassemble, reverse the procedure.

Gearboxes for DC motors

For its DC motors, igus has so far offered permanently mounted planetary, spur gear and worm gearboxes. These are available in a wide range of configurations and in different speeds, rated torques and, of course, starting torques.

The DC motors have a standard protection class of IP20 - IP30. This means that they are protected against the ingress of foreign bodies. To provide even better protection, igus also has Protect DC motors in its portfolio, which have a protection class of IP40, and thereby are resistant to the ingress of small foreign bodies, e.g. dust larger than 1mm.