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I am trying to get a sensored bldc motor to spin by building my own ESC. I have the complete circuit built and working perfectly, but i'm having trouble with the sensors.

Recently something weird has happened. The sensors are rotating through the 6 phases as I rotate the motor by hand, but what's weird is that I completely unplugged the bldc motor phase wires from the power source (while still powering the sensor pins with 5 volts) and when I continue to rotate the shaft the sensors continue to rotate through the 6 phases. It should be reading LOW for all sensors no matter where I rotate the motor because there should be no current flowing through the motor, but the sensors are still detecting a high signal.

Something else that is weird is normally the 6 phases that your sensors detect are 100, 010, 001, 110, 011, 101, but my sensors are detecting 111, 110, 100, 000, 001, 011 as I rotate the shaft. Does anyone know why this is happening?

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  • \$\begingroup\$ Please can we have link to your motor? \$\endgroup\$
    – tlfong01
    Jul 2, 2022 at 4:21
  • \$\begingroup\$ Or are your Hall sensor similar to this? 3-Phase Brushless DC Motor Control with Hall Sensors - Oleg Basovych, Dialog Semiconductor, 2018jun26 allaboutcircuits.com/industry-articles/… \$\endgroup\$
    – tlfong01
    Jul 2, 2022 at 4:30
  • \$\begingroup\$ @tlfong01 here is the link to my motor: amazon.com/dp/…. \$\endgroup\$
    – Trev347
    Jul 2, 2022 at 4:32
  • \$\begingroup\$ Your link is in Chinese. I guess this an English equivalent: Electric Skateboard Motor, 6374 DC 36V Motor Hall Sensor, High Torsion Mountain: Remote Control Car Outer Rotor with Connector Terminals for Skateboard - Hyuduo US$147 amazon.com/Electric-Skateboard-Mountain-Connector-Terminals/dp/… \$\endgroup\$
    – tlfong01
    Jul 2, 2022 at 4:43
  • \$\begingroup\$ Honestly have no idea why its Chinese for you cause its English for me haha. But yeah thats pretty much the same motor what you have there. \$\endgroup\$
    – Trev347
    Jul 2, 2022 at 4:45

1 Answer 1

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They are sensing the magnetic field, not the current, to detect the position of the magnetic poles. It doesn't make any sense to sense current because current doesn't tell you the relative positions of the rotor and stator poles. What did you think the sensors were supposed to do? (this isn't meant to be rhetorical, I want to know)

Something else that is weird is normally the 6 phases that your sensors detect are 100, 010, 001, 110, 011, 101, but my sensors are detecting 111, 110, 100, 000, 001, 011 as I rotate the shaft. Does anyone know why this is happening?

It is using one-hot encoding which means only one bit changes between adjacent states. That's because in an unclocked system, you cannot rely on two bits to transition at exactly the same time. The result is that it will momentarily stutter on an intermediary state that was never meant to be which can obviously cause issues.

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  • \$\begingroup\$ I understand that they aren't measuring current, but without current there wouldn't be a magnetic field. So how are they sensing a magnetic field if no current is flowing? \$\endgroup\$
    – Trev347
    Jul 2, 2022 at 4:26
  • \$\begingroup\$ @Trev347 Are you forgetting about the permanent magnets? \$\endgroup\$
    – DKNguyen
    Jul 2, 2022 at 4:27
  • \$\begingroup\$ I remembered those, but I assumed the sensors would only sense the electric magnets. If they sense both permanent and electric magnets then how do you know what phase you are in cause the permanent and electric magnets would get mixed? \$\endgroup\$
    – Trev347
    Jul 2, 2022 at 4:30
  • \$\begingroup\$ A magnetic field is a magnetic field. The sensors can't tell the difference. I am unsure of the specifics but the sensors either need to be positioned appropriately in the motor so they are only sensitive to the field of the permanent magnets and positioned or you ignore the sensors that you know are picking up the coil magnetic field (since you know which coils are energized). \$\endgroup\$
    – DKNguyen
    Jul 2, 2022 at 4:32
  • \$\begingroup\$ Yes that's what I assumed the bldc motor would be doing. But since thee sensors are sensing high signals even though there is no current running through the electric magnets doesn't that mean they are sensing the permanent magnet? \$\endgroup\$
    – Trev347
    Jul 2, 2022 at 4:33

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