3 Phase Brushless Motor

Discussion in 'General Electronics Chat' started by bwilliams60, Mar 28, 2014.

  1. bwilliams60

    Thread Starter Active Member

    Nov 18, 2012
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    88
    Todays dumb question. I have a small DC motor out of an RC airplane and I am told that it is a 3 phase brushless motor. I always thought 3 phase would come in a much larger motor so I am questioning whether it is AC or DC? It has three wires coming out of it going to a controller or ESC. To my way of thinking, it would have to have a minimum of four wires if it was wye wound and six if delta. Can someone clear up the mud for me. How is this a motor and not a generator?
    Here is a picture of the motor.

    http://www.electrifly.com/motors/gpmg5105.html

    Motor # GPMG 5185
    Thank you in advance.
     
  2. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,503
    2,366
    If it is a 3phase it is what is termed an outrunner or inrunner depending on whether wound armature and the rotor turns or vice versa.
    It would only require 3 wires if connected Star or Wye.
    Google Outrunner and Inrunner.
    Max.
     
    Last edited: Mar 28, 2014
  3. bwilliams60

    Thread Starter Active Member

    Nov 18, 2012
    722
    88
    Hey Max, Thanks for the heads up. Right after I posted it, i drove home from work and figured it out on the way but didn't realize that such a small motor could be 3 phase. After reading your post I found this information and now I am educated. I love when students ask me questions that I can't answer right away. I am all about DC so every time I get an AC question, I learn something new. It turned out to be a great homework question for them, and an education for me. We all win. Thanks again

    http://www.rcuniverse.com/magazine/article_display.cfm?article_id=1344
     
  4. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,503
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    The type of RC AC servo motor is a bit different to the industrial BLDC or AC sinusoidal motors used in robotics or CNC controls, as these usually have some kind of rotor position sensors in order to commutate and run at a synchronous speed.
    Max.
     
  5. leif26

    New Member

    Jul 26, 2010
    3
    0
    I have been playing with a 3-phase HD brushless motor. All of the diagrams of other 3-phase brushless motors show stators that are staggered i.e. a-b-c, a-b-c, a-b-c, but this one is just ABC even though there are nine poles. How can this be efficient, and what is the cheapest way to control this motor?
    Thanks


    https://www.flickr.com/photos/leifmag/14021299897/in/photostream/
     
  6. MaxHeadRoom

    Expert

    Jul 18, 2013
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    That appears to be an outrunner of the RC variety, a RC motor controller may fit the bill?
    That would normally be labeled an 8 pole motor with 4 electrical revolutions/ mechanical rev.
    Max.
     
    Last edited: May 17, 2014
  7. leif26

    New Member

    Jul 26, 2010
    3
    0
    I have a motor controller that works fine on some small dvd player motors, but after unsuccessfully trying to run this motor I opened it up and unwound the motor and realized that the stators are wound in a row rather than alternating, i,e abc, abc, abc, etc. How could this motor run even if you had the right controller for it? It seems like the stators would be pushing and pulling the rotor, wouldn't it be fighting itself? The 5V motor is from a 2.5" hard drive. There are three wires that run the motor.

    https://www.flickr.com/photos/leifmag/14021299897/in/photostream/
     
    Last edited: May 18, 2014
  8. MaxHeadRoom

    Expert

    Jul 18, 2013
    10,503
    2,366
    Study the BLDC motor, they range from 2pole up to 8 pole on average, the electrical rotations conform to the pole count/2.
    They are the more conventional stator wound motor where the rotating field is on the outside stator and the P.M. field is on the rotor.
    If you rotate either a BLDC or the outrunner type without power, you will see the 3 phase generated in the stator as per the attached PDF.
    This helps understand the reverse, when you supply the stator and therefor the effect on the rotor.
    Max.
     
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