What is the minimum shaft distance required to do a shaft coupling.

I want to mount encoders on my motors but the shaft length is only 15 mm long. My encoders are 12 mm wide. So, I only have 3 mm to do a shaft coupling.

The motors are this

The shaft have a diameter of 6 mm and the motors have a stall torque of 416 oz-in (30 kgf-cm). I am planning to do a 6mm to 6mm shaft coupling and I was wondering if 3 mm is enough distance. I want to mount the encoders like in the picture. From a graph in the motor website I think the power is around 15 Watts.


  • $\begingroup$ what does the other end of the motor shaft look like? $\endgroup$
    – jsotola
    Mar 13, 2019 at 20:26
  • $\begingroup$ @jsotola just the wheel, I need another 15 mm to mount the wheel of my robot. My concern is the torque on the motors, I think is high $\endgroup$
    – Luis
    Mar 13, 2019 at 20:41
  • $\begingroup$ i asked about the motor shaft ..... in the picture above, it is to the left $\endgroup$
    – jsotola
    Mar 14, 2019 at 18:02

1 Answer 1


If it is the same type of shaft coupling as the one in the picture, as long as the set screw is completely on the motor shaft, it will transfer adequate torque. To help with the limited clearance, ensure no pulling force is apply to the coupler since it might slip out of the coupler. The motor shaft and the coupled rod must perfectly straight to reduce the chance of the set screw to "dig" itself out of the motor shaft.


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