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Sensored BLDC Motor Question ...

Discussion in 'Sensors and Actuators' started by Fish4Fun, Mar 30, 2020.

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  1. Fish4Fun

    Fish4Fun So long, and Thanks for all the Fish!

    464
    105
    Aug 27, 2013
    So I ordered one of these:

    https://www.ebay.com/itm/4600W-6384-120KV-BLDC-Outrunner-Sensored-Brushless-Motor-For-Electric-Skateboard/164069170610?ssPageName=STRK:MEBIDX:IT&_trksid=p2057872.m2749.l2649

    I am attempting to build a driver for it, but I expected the sensors to have outputs like this:

    [​IMG]

    OR the Hall Effect elements themselves to be Bi-Polar and alternate between 1/4V - 1/2V - 3/4V depending on Field, ie: >> North - None - South << ie Like this:

    upload_2020-3-30_9-47-39.png



    What I was NOT prepared for was the following:

    upload_2020-3-29_11-25-20.png

    Assuming the sensors are bits arranged ABC and that each sensor combination should have a "fixed period" for any given rotational velocity, then the sensors should progress through 6 distinct "steps" with roughly equal periods (like the first reference diagram above) ... Like this:

    Code:
    (Assuming the period per field is 3m/s (~55.5hz output)
    001=> 3ms
    011=> 3ms
    010=> 3ms
    110=> 3ms
    100=> 3ms
    101=> 3ms
    -----------
    001=> 3ms
    011=> 3ms
    010=> 3ms
    110=> 3ms
    100=> 3ms
    101=> 3ms
    .---------
    .
    etc
    
    What I am seeing progresses through 6 steps, but two of the steps have a much larger period than the other 4 steps .... As Follows:

    Code:
    000 => 3.0mS
    010 => 2.6mS
    011 => 4.4mS  *******
    111 => 3.4mS
    101 => 2.0mS
    100 => 5.0ms  *******
    ----------------------
    000 => 2.6ms
    010 => 2.6mS
    011 => 5.0ms  *******
    111 => 2.8ms
    101 => 3.0ms
    100 => 4.6mS  *******
    -----------------------
    .
    .
    .
    etc
    
    What I don't know is if these "mismatched" timing cycles are by design or represent a flaw in the production of this particular motor. I have measured the sensors at various rotational rates and very consistently found every third pulse to be slightly less than twice the period of the two preceding and following pulse periods.

    I have NOT disassembled the motor to take a look at the Hall Effect sensor PCB. The sensor outputs DO require pull-up resistors to function properly, but I don't know if this implies unipolar Hall Effect sensors or Bipolar Hall effect sensors with comparator outputs ...

    I was honestly expecting either 3 bipolar sensor outputs OR six sensor outputs (AH AL BH BL CH CL as typically found in a brushless servo). I am not exactly sure how to use the six sensor steps to produce a an output waveform that makes sense. Perhaps I am missing something obvious, but I can't think what it might be .... so any help would be appreciated!

    Thanks in advance!

    Fish[/Code]
     
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