• Educate me on these motor waveforms.

    From amdx@21:1/5 to All on Wed May 4 09:58:56 2022
     My son built a an electric skateboard and then ask me about how the
    motors work.
    I made and assumption that they were 3 phase motors (3 wires) and I
    would see a
    high frequency AC current waveform. I have not looked at the voltage, I
    used an
    inductive clip to look at the current waveform. The pictures show the
    wave forms
    at different throttle inputs. Right now it is software limited to 30% of
    max,
    so I can't show what 90% or 100% throttle looks like.
     To me, the wave forms looks like PWM, at least at the very start after
    that,
    I'm asking for someone to explain what is going on.
    https://www.dropbox.com/s/cmsdyng4p5nx1lt/Motor%20Waveforms.jpg?dl=0

                                Mikek

     PS. probably doesn't matter, but my inductive clip is an old clip used to monitor spark plug wires. It was a big signal out at 100kHz but at 100 Hz,
    the signal is way down, dare I say 1/600! So, could the wave form be
    missing
    some low frequency information, confusing the issue?

    PSS, even with a 30% software drive limit, it still goes 17 miles an
    hour, drat,
    I tried to change his mind to build a bicycle.


    --
    This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Lasse Langwadt Christensen@21:1/5 to All on Wed May 4 09:07:37 2022
    onsdag den 4. maj 2022 kl. 16.59.06 UTC+2 skrev amdx:
    My son built a an electric skateboard and then ask me about how the
    motors work.
    I made and assumption that they were 3 phase motors (3 wires) and I
    would see a
    high frequency AC current waveform. I have not looked at the voltage, I
    used an
    inductive clip to look at the current waveform. The pictures show the
    wave forms
    at different throttle inputs. Right now it is software limited to 30% of
    max,
    so I can't show what 90% or 100% throttle looks like.
    To me, the wave forms looks like PWM, at least at the very start after
    that,
    I'm asking for someone to explain what is going on.
    https://www.dropbox.com/s/cmsdyng4p5nx1lt/Motor%20Waveforms.jpg?dl=0

    Mikek

    PS. probably doesn't matter, but my inductive clip is an old clip used to monitor spark plug wires. It was a big signal out at 100kHz but at 100 Hz, the signal is way down, dare I say 1/600! So, could the wave form be
    missing
    some low frequency information, confusing the issue?

    PSS, even with a 30% software drive limit, it still goes 17 miles an
    hour, drat,
    I tried to change his mind to build a bicycle.


    I suspect your timescale is way to short so you only see the pwm

    https://www.physicsforums.com/attachments/bldcemf-png.47285/

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From three_jeeps@21:1/5 to amdx on Wed May 4 13:40:35 2022
    On Wednesday, May 4, 2022 at 10:59:06 AM UTC-4, amdx wrote:
    My son built a an electric skateboard and then ask me about how the
    motors work.
    I made and assumption that they were 3 phase motors (3 wires) and I
    would see a
    high frequency AC current waveform. I have not looked at the voltage, I
    used an
    inductive clip to look at the current waveform. The pictures show the
    wave forms
    at different throttle inputs. Right now it is software limited to 30% of
    max,
    so I can't show what 90% or 100% throttle looks like.
    To me, the wave forms looks like PWM, at least at the very start after
    that,
    I'm asking for someone to explain what is going on.
    https://www.dropbox.com/s/cmsdyng4p5nx1lt/Motor%20Waveforms.jpg?dl=0

    Mikek

    PS. probably doesn't matter, but my inductive clip is an old clip used to monitor spark plug wires. It was a big signal out at 100kHz but at 100 Hz, the signal is way down, dare I say 1/600! So, could the wave form be
    missing
    some low frequency information, confusing the issue?

    PSS, even with a 30% software drive limit, it still goes 17 miles an
    hour, drat,
    I tried to change his mind to build a bicycle.


    --
    This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus

    typically these are brushless DC motors. The electronic speed controller controls the torque by PWM the current into motor. Typically the control voltage is 12v, but the current can be very high, 100A+

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From Phil Allison@21:1/5 to amdx on Wed May 4 14:31:20 2022
    amdx wrote:

    ==========

    My son built a an electric skateboard and then ask me about how the
    motors work.
    -------
    I have not looked at the voltage, I used an
    inductive clip to look at the current waveform.

    ** That dumb idea will never work.

    It's a BLDC motor and there are hundreds of pages on the net about them.
    Shame most of them make no sense.


    ..... Phil

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)
  • From amdx@21:1/5 to Phil Allison on Wed May 4 21:35:14 2022
    On 5/4/2022 4:31 PM, Phil Allison wrote:
    amdx wrote:

    ==========

    My son built a an electric skateboard and then ask me about how the
    motors work.
    -------
    I have not looked at the voltage, I used an
    inductive clip to look at the current waveform.
    ** That dumb idea will never work.

    It's a BLDC motor and there are hundreds of pages on the net about them. Shame most of them make no sense.


    ..... Phil
    Are you talking about the inductive clip not working?
    If so, why?
                          Mikek

    --
    This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus

    --- SoupGate-Win32 v1.05
    * Origin: fsxNet Usenet Gateway (21:1/5)