How to find the torque constant of BLDC motor?

[AFZAL AMANULLAH]

Hello Friends,
I have used in-wheel BLDC motor for my experiment. In this type of motor BLDC motor inbuilt on wheel. This wheel is a part of electric scooter. I wated to find the value of torque constant and back emf constant. Also how to measure torque for a selected current.
Please help me.
Thanks

 

[Asymptotic]

Is the motor manufacturer, and part number known? The easiest way is to pull them from motor specifications.

Torque constant is the relationship between torque and current (K_t=Torque/Ampere). Measure generated torque, and the amount of current required to generate it. Divide.

how to measure torque

One way to measure stall torque is to do something similar to what was done here ...

... but use a spring scale instead of a weight.

Alternatively, connect the motor shaft directly to a torque wrench, and read it directly.
If necessary, a prony brake can be devised to measure rotating torque.

Back EMF is generated by rotor/stator interaction whenever the rotor is turning. Connect the BLDC motor-under-test to an external source of rotational motion, measure shaft speed, and generated stator voltage.

This application note ought to be helpful.

 

[AFZAL AMANULLAH]

In BLDC motor is Kt = Ke ?

how to measure R, La ?
My hub motor is attached herewith.

 

[Asymptotic]

In BLDC motor is Kt = Ke ?
Ideally yes, but in practice, probably not.

What units are Kt and Ke in?
Kt=Nm/A (Nm=Newton-meters; A=Amperes)
Ke=RPM/V (RPM=Revolutions per minute; V=Volts). Note: Ke may be stated as the reciprocal (Volts/RPM).

Look up the specs for your motor, or another one in your size and power range to get a feel for what values make sense.
For instance, for the Xnova 4025-670KV 2.5Y motor, Ke is 670 RPM/V (0.00149 V/RPM), and Kt is 0.0143 Nm/A.

how to measure R, La ?
An ohmmeter with a low resistance range (or a milliohmmeter) and LCR meter come in handy.