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how to calculte B-EMF constant from torch constant

Associate II

Hi, I'm working with an Maxon 3-phase 1-pole BLDC motor, following is it's motor data table or attached file. the colum with red rectangle is the motor type we're now dealing with.

I wondering how can we get the B-EMF constant in the MC workbench electrical parameters from this motor data.

And what's the speed constant related with B-emf constant. isn't it b-emf constant reciprocal 

motor param 24V.png


 The motor controller we use is B-G431B-ESC1 Discoery kit, would that board sufficent to driving this maxon motor?

We also try to use the motor profiler to get the motor parameters,but the progress bar always stay at 7% or 14% and giving us the max speed setting warning.

Looking forward to your feedback, Thank you!


Gael A
ST Employee

Hello jflash,

You can easily get your BEMF constant using our provided MotorProfiler tool, please update your MCSDK version to our latest (6.2) if you have any profiling issue. It is delivered within the MotorPilot tool. you will find its startup guide right here. This will allow you to create a configuration file for your Maxon motor. It will be saved as a referenced motor and you won't need to manually enter your motor's characteristics every time you want to build a project.

Your B-G431B-ESC1 inverter board should be able to run your motor, also be aware that this board is intended to be used with a cooling device (usually a fan), as it may heat up very quickly. If you want to proceed with the profiling (and running) without any cooling device, you may need to lower the max current when profiling, so it can end the profiling without potentially damaging your board. You will get wrong max speed, but the other parameters will be calculated correctly. You can then edit your Motor file manually to change the max speed.

If you agree with my answer, please consider accepting it by clicking on 'Accept as solution'.

Hope this will help,
Gaël A.

Hi,Gael A. Thanks for your help.

We have tried profiling this motor before, but the Profiler just can't come to 100%, it always stays at 7%, sometimes may reach at 14%, and why giving us that the max speed specification should be reviewed? the max speed is cirtical in the profiling process?  The max speed we set is 30000 rpm and  max current is 3.29A, when profiling.   Any suggestions? Thanks!profiler.PNG

Gael A
ST Employee

Hello jflash,

May I know the Profiler version you are using on which you are experiencing issues ?
Please make sure you have our latest version installed (MCSDK 6.2) ; it provides a few fixes concerning Motor Profiler.
If you are still experiencing the same kind of issues, you can also try tinkering a bit with the Max Speed and Max Current values, reducing them for instance. This will not hinder the calculation of your BEMF constant.  Your motor configuration file will get wrong Max Speed and Max Current values, but you can still modify them afterwards.

If you agree with my answer, please consider accepting it by clicking on 'Accept as solution'.

Hope this will help,
Gaël A.

Hi, Gael A. Thanks for your help.

The SDK version we are using is already 6.2.0.  There's something may cause the progress failing, but I'm not sure if that's the problem. The on board shunt resister of B-G431B-ESC1 Discoery kit is 3mOhm, but the back-emf constant of the Maxon motor we use is about 0.5Vrms/kRPM, We use the default example project of B-G431B-ESC1 kit and the  Internal PGA Gain in the current sensing page is 16, giving us the readable current range as 

[-75.05 A, 45.35 A] → ± 45.35 A
Are these settings not fitted for the Maxon motor we're using? I think the readable range of shunt current should just cover the norminal current, so that the ADC of the control board can sample it precisely for motors with small back-emf constant. We want to change the shunt resisters on board to 300mOhm, and decrease the PGA Gain to 2, so that the readable current range sits in about [±3.6A]. I don't know if  there's any risks we change the shunt resister from 3mOhm to 300mOhm. And just wondering if the 3mOhm shunt resistor on this dev kit is ok for our testing Motor.