Is this a 120 or 60 deg displacement angle hall motor?

[hmc]

Hello forum! I am trying to characterize a motor for experimentation with the workbench. I spun the rotor with a hand drill and got the following waveform, with the first 3 channels being H1, H2, H3 and the analog voltage being the back-EMF from the motor phase C. It looks to me like this is a 120 deg phase offset between each hall sensor, and since the channel back-EMF is 22 deg AHEAD of the H3, the placement electrical angle should be -22 deg, in the workbench motor parameters. Do you think I am misunderstanding the definition of the these values?

Thanks for reading.

Note the actual form factor of the hall sensor is within the 60 deg region of the stator.

[uomo motore · Accepted solution]

If channel 2 is H1, channel 1 is H2 and channel 0 is H3 then hall sensors are 120 degrees electrical apart. Mechanical placement can be within 60 degrees physically. It is the electrical displacement that matters.

What is the reference for the channel C BEMF waveform capture? Is it with respect to motor star point?

[Dario CUCCHI]

Hello @hmc​,

Let me just add that, in the MCSDK the motor parameter, the “Placement electrical angle�? of the Hall sensor is defined as:

the phase in degrees between the rising edge of the H1 sensor and the maximum of the BEMF on phase A, measured respect the central tap of the motor.

If you have other questions, feel free to ask :smiling_face_with_smiling_eyes:

Otherwise, please consider to mark the answer above by @uomo motore​  as best.

This will help other users in the community who are looking for the same information.

Thanks and All the best !

[hmc]

Perhaps should be obvious, but I guess you are defining the BEMF(A) lagging the H1 edge as positive?

[Dario CUCCHI]

Yes exact !

Look at this example:

You can see, for this specific motor, the BEMF is lagging 120° the H1 positive edge: so in the workbench the “Placement electrical angle�? must be set at 120°.

[MK.1]

Hello, Dario Cucchi!

If you follow the documentation, then the angle in the figure is 240 degrees.

UM1052, 93/178

5. Measure the delay in electrical degrees between the maximum of the B-emf induced on phase A and the first rising edge of signal H1.

6. Enter two parameters displacement and delay found in the ST MC Workbench GUI, inside the window related to motor speed and position sensor. An example with delay equal to 270° is illustrated in Figure 85: "Determination of Hall electrical phase shift"

Thanks.

[Dario CUCCHI]

Hello @MK.1​  !

Yes, you are right: in the user manual UM1052 the procedure describes that the angle is measured from the maximum of the B-emf induced on phase A to the first rising edge of signal H1.

However, this is referred to the specific case where the sequence of the Hall sensors is H1 rising edge, H2 rising edge, H3 rising edge.

See point 4 at page 93 in the UM1052.

So, the procedure is referred to a specific spinning direction.

In the example I provided the sequence is:

H3 rising edge, H2 rising edge, H1 rising edge so in this case the motor is rotating in the opposite direction.

Since we have an opposite direction, we also need to revert the phase shift calculation so:

from the first rising edge of signal H1 to the maximum of the B-emf induced on phase A.

Now I realize that this picture could be misleading , so thanks for your clarification :grinning_face_with_sweat:.

Let me take the chance to better explain and avoid any confusion !

I took the same motor of the previous acquisition and I did an acquisition making it spinning in the direction shown in the user manual UM1052.

As you can see now measuring from the maximum of the B-emf induced on phase A to the first rising edge of signal H1 I get 120° as in the previous case: and this the value to be set in the "Placement electrical angle".

Sorry if I wasn’t clear from the beginning, I hope now it is ok.

[MK.1]

Thank you Dario, this is an important point!

[Laurent Ca...]

The question has been moved from the "STM32 Motor Control" section to the "Motor Control Hardware" section (the question is not about the STM32 MC SDK). 

Best regards