How to Select a Coupling for my motor

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Joined: Tue May 10, 2016 4:48 pm

How to Select a Coupling for my motor

Postby om_tech_support_JS » Tue Mar 06, 2018 9:41 am

Q: My application is for a mixer that requires an induction motor with a shaft length of 6 inches, but the 4IK25A-AW2U only has a shaft length of 1.26 inches. I would like to find a coupling that I can extend the shaft length with, but there are no recommended couplings in the accessory section of this motor. How do I pick out a coupling for this?

A: Couplings (also referred to as couplers) are devices used to connect two shafts together. In applications, the motor shaft and drive shaft can either be the same size, or different sizes. For this reason, Oriental Motor offers a wide variety of flexible couplings to choose from. Typically, the recommended couplings for a motor will be listed on the right hand side of our webpage; however when you do not see the size that you require, or in the event that there are none recommended, then you can still make a selection from the couplings that we offer. In order to select the appropriate coupling, you must understand and consider the following information.

We offer three different series of couplings: MCL, MCS, and MCV series. The MCL series couplings are fitting for high torque applications, however they are the most basic models and are, therefore, recommended for use with our induction motors. The MCS series couplings are rated for high strength and there is no backlash, therefore, this series is typically recommended for our stepper motors. Lastly, the MCV series couplings can be used for anti-vibration purposes, there is no backlash, it has high response, and the rubber from the couplings provide electrical insulation. The MCV series is typically recommend on our servo motors.

When looking to select a coupling, keep the previous information in mind as it could alter the results of your application. For instance, if you select an MCL type coupling for a stepper application, then additional backlash may be generated from the coupling; however moving ‘up’ from an MCL to MCS type coupling on an induction motor would not negatively affect the application.

The following page can be used to select a coupling after indicating the desired parameters: Required torque, shaft 1 diameter, and shaft 2 diameter: ... -couplings

To ensure that the appropriate coupling was chosen from the list, there are a few specifications to verify compatibility with your motor. We will go through all the parameters using this case as an example:

- Shaft hole diameter
There are two diameters that you would have to consider, the diameter for the motor shaft and the diameter for the drive shaft. For our couplings, the two diameters are defined as d1: for motor shaft and d2: drive shaft.

Coupling Selection from List.png
Coupling Selection from List.png (174.14 KiB) Viewed 4095 times

Only MCL and MCS offer couplings for keyed shafts for select models. Please be sure to check in the dimensions for the keyed shaft specifications when selecting a coupling. In our case, the MCS200808 fits both output shaft diameters that we are looking for as the 4IK25A-AW2U motor has an 8 mm output shaft. In this case, the two output shaft diameters that we are looking to couple together are the same, that is not always the case as couplings can have different shaft hole diameters on the two ends of the coupling.

- Motor output torque vs. normal torque

Once a coupling is picked, we will also have to make sure that the torque specifications are compatible between the motor and the coupling. The normal torque value specifies the maximum permissible torque that the motor can output to the coupling without damaging the coupling. The rated torque value for the 4IK25A-AW2U is 0.17 Nm and the normal torque specification for the MCS200808 coupling is 5 Nm. So the torque specifications are compatible as well.

- Alignment specifications

We will then check to see if there are any possible mis-alignments that we should be aware of for this application. There are three types of alignments that we look into- eccentricity, declination and end play. Since our couplings are flexible couplings, the permissible misalignments should be taken into consideration as well.

Alignment.png (29.23 KiB) Viewed 4095 times

Eccentricity refers to the offset between the motor shaft going into the coupling and the drive shaft. The Declination is for when the drive shaft is not aligned at 180 degrees with the motor shaft. Lastly, the End play is referring to the axial movements during operation.

In this case, since the drive shaft will be aligned with the motor shaft at 180 degrees with no declination and end play, the coupling MCS200808 will fit for the application.

- Backlash from the coupling
For applications where no backlash is required, the MCS or MCV type couplings would work. The selection process would be the same as above. Since AC motor applications do not require non-blacklash couplings, MCL is typically used for AC and the recommendations in the AC motor accessories only show MCL couplings. If needed, the other series that we offer: MCS and MCV, can also work for AC motor applications. MCL couplings are not recommended for positioning applications as backlash may occur.

- Static torsion spring constant

The static torsion spring constant is used to determine if the coupling is high response. The constant’s unit is Nm/rad or lb-in/rad, which represent how much torque the coupling will reflect for each radian the coupling is rotated. The higher the static torsion spring constant, the higher the response from the coupling you will get. For example, for two couplings that are similar in specifications: MCV190808 vs. MCS200808, their static torsion constant are shown below:

Static Torsion Spring Constant MCV.png
Static Torsion Spring Constant MCV.png (149.96 KiB) Viewed 4095 times

Static Torsion Spring Constant MCS.png
Static Torsion Spring Constant MCS.png (121.88 KiB) Viewed 4095 times

Since the coupling type and the diameter specifications are very similar, the MCV has significantly higher static torsion spring constant, which means the response is higher. With applications where positional accuracy is needed, highly responsive couplings would fit best.

- Maximum torque vs. Normal torque
With The MCV type couplings, there are two different torque specifications – maximum torque and normal torque. The maximum torque specification is for operating the motor in limited duty region, which is not for continuous operation. The normal torque specification is for continuous operation.

Picking out a fitting coupling for individual applications can be done with following the above parameters. Please contact tech support if you need additional assistance with picking out a coupling.

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