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How to stop electrical whining noise?

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Tauno Voipio
Guest

Wed Dec 26, 2018 8:45 pm   



On 26.12.18 20:45, Jeff Liebermann wrote:
Quote:
On Wed, 26 Dec 2018 11:01:56 -0500, bitrex <user_at_example.net> wrote:

Here's some interesting papers on sources of noise from small DC motors:
https://www.mdpi.com/2072-666X/9/2/84/pdf
http://downloads.hindawi.com/journals/ijrm/2006/063214.pdf
The first seems to indicate a significant source of noise at high freq
in small motors is excited resonance of the motor housing itself

Suggestion: Remove the propellers from the quadcopter and run the
motors without the props. The residual noise should be 100% chopper
noise. I did that in the past on my Walkera XR-350 clone:
http://www.learnbydestroying.com/jeffl/pics/drivel/slides/Walkera%20QR%20X350%20Drone.html
and heard very little remaining noise from the motors. However, my
hearing is not the best, and I didn't bother making any measurements
with an SPL meter. If I find time, I might try it again later today.


If you remove the propellers, you should substitute a
comparable amount of torque load to keep the operating
conditions. The noise will be significantly lower when
there is no torque load.

--

-TV

John Doe
Guest

Thu Dec 27, 2018 12:45 am   



tabbypurr_at_gmail.com wrote:

Quote:
bitrex wrote:
Klaus Kragelund wrote:

It sounds to me like it is switching noise from the motor drive,
which causes movement of the motor windings

It sounds to be a steady noise frequency which it won't be if
it is related to the blades. No way to change it, except to
change the motor control SW or filter the output to the motor to
reduce the switching current ripple

if it's electrically excited/resonant acoustic noise caused by a
specific PWM harmonic in the audible range (the whine seems to be
consistent in frequency across the motor power output range) what
about a parallel-series LC band-reject in the PWM drive output to
the motors?

The armature can't resonate at that frequency if it can't get any
power from the controller at that frequency

The whining noise is clearly constant frequency as the motors pick
up speed, and can't possibly be produced by the propellors. There
are 2 solutions:
1. move to an ultrasonic switching frequency
2. Infiltrate varnish etc into the switched mode inductor & put foam
under the PCB it's on.


There is no such sound on most other drones.

Jeff Liebermann
Guest

Thu Dec 27, 2018 2:45 am   



On Wed, 26 Dec 2018 21:43:53 +0200, Tauno Voipio
<tauno.voipio_at_notused.fi.invalid> wrote:

Quote:
On 26.12.18 20:45, Jeff Liebermann wrote:
On Wed, 26 Dec 2018 11:01:56 -0500, bitrex <user_at_example.net> wrote:

Here's some interesting papers on sources of noise from small DC motors:
https://www.mdpi.com/2072-666X/9/2/84/pdf
http://downloads.hindawi.com/journals/ijrm/2006/063214.pdf
The first seems to indicate a significant source of noise at high freq
in small motors is excited resonance of the motor housing itself

Suggestion: Remove the propellers from the quadcopter and run the
motors without the props. The residual noise should be 100% chopper
noise. I did that in the past on my Walkera XR-350 clone:
http://www.learnbydestroying.com/jeffl/pics/drivel/slides/Walkera%20QR%20X350%20Drone.html
and heard very little remaining noise from the motors. However, my
hearing is not the best, and I didn't bother making any measurements
with an SPL meter. If I find time, I might try it again later today.

If you remove the propellers, you should substitute a
comparable amount of torque load to keep the operating
conditions. The noise will be significantly lower when
there is no torque load.


I could do that using a disk (washer) with a radius of about 30% of
the propeller radius (center of mass) and having the same weight as
the four propellers. I think I have some spare props left over from
my last attempt at indoor flying (before I added the shrouds). It's
not a good equivalent load torque because it's not pushing air, but
methinks the inertial load of the disk (washer) will be sufficient to
have the chopper produce some vibrations.

However, I won't have time for a few days. The doctors will be
removing two large kidney stones tomorrow and I may need some time to
recover. To be continued when possible.



--
Jeff Liebermann jeffl_at_cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Jeff Liebermann
Guest

Thu Dec 27, 2018 2:45 am   



On Wed, 26 Dec 2018 07:51:31 -0000 (UTC), John Doe
<always.look_at_message.header> wrote:

Quote:
bitrex <user_at_example.net> wrote:

Klaus Kragelund wrote:

It sounds to me like it is switching noise from the motor drive,
which causes movement of the motor windings

It sounds to be a steady noise frequency which it won’t be if
it is related to the blades

No way to change it, except to change the motor control SW or
filter the output to the motor to reduce the switching current
ripple

I hear it now. Had to put on headphones, on laptop speakers I only
hear the lower pitched blade noise

I was just coming back to post about that possibility. The frequency
is at least 8 kHz. A bad sound system or failing ears might not even
know what sound we're talking about.


<https://www.youtube.com/watch?v=FSwZQtqWyHw>
Audio spectrum from the YouTube video:
<http://www.learnbydestroying.com/jeffl/crud/drone-noise-spectrum-01.jpg>
Peaks at 300Hz, it's harmonics, and chopper noise at about 8KHz.
However, the rather high broadband audio noise level is quite real.
Removing the 300 and 8000Hz tones would probably not have much of an
effect on the overall noise level, which would still sound like white
noise air turbulence, similar to the noise from a compressed air
nozzle.


--
Jeff Liebermann jeffl_at_cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

John Doe
Guest

Thu Dec 27, 2018 3:45 am   



Jeff Liebermann <jeffl_at_cruzio.com> wrote:

Quote:
John Doe <always.look_at_message.header> wrote:
bitrex <user_at_example.net> wrote:
Klaus Kragelund wrote:

It sounds to me like it is switching noise from the motor
drive, which causes movement of the motor windings

It sounds to be a steady noise frequency which it won’t be if
it is related to the blades

No way to change it, except to change the motor control SW or
filter the output to the motor to reduce the switching current
ripple

I hear it now. Had to put on headphones, on laptop speakers I
only hear the lower pitched blade noise

I was just coming back to post about that possibility. The
frequency is at least 8 kHz. A bad sound system or failing ears
might not even know what sound we're talking about.

https://www.youtube.com/watch?v=FSwZQtqWyHw

http://www.learnbydestroying.com/jeffl/crud/drone-noise-spectrum-01.jpg

Removing the 300 and 8000Hz tones would probably not have much of
an effect on the overall noise level


Maybe because you can't hear it. It makes a big difference to me.
Shown by pulling my 8 kHz equalizer slider down to zero.

You say "I never guess". You might want to start.
Even Blinkin was guessing, and he could at least hear...

https://youtu.be/zJQ7FxLzhVs

Phil Hobbs
Guest

Thu Dec 27, 2018 4:45 am   



On 12/26/18 7:51 PM, Jeff Liebermann wrote:
Quote:
On Wed, 26 Dec 2018 21:43:53 +0200, Tauno Voipio
tauno.voipio_at_notused.fi.invalid> wrote:

On 26.12.18 20:45, Jeff Liebermann wrote:
On Wed, 26 Dec 2018 11:01:56 -0500, bitrex <user_at_example.net> wrote:

Here's some interesting papers on sources of noise from small DC motors:
https://www.mdpi.com/2072-666X/9/2/84/pdf
http://downloads.hindawi.com/journals/ijrm/2006/063214.pdf
The first seems to indicate a significant source of noise at high freq
in small motors is excited resonance of the motor housing itself

Suggestion: Remove the propellers from the quadcopter and run the
motors without the props. The residual noise should be 100% chopper
noise. I did that in the past on my Walkera XR-350 clone:
http://www.learnbydestroying.com/jeffl/pics/drivel/slides/Walkera%20QR%20X350%20Drone.html
and heard very little remaining noise from the motors. However, my
hearing is not the best, and I didn't bother making any measurements
with an SPL meter. If I find time, I might try it again later today.

If you remove the propellers, you should substitute a
comparable amount of torque load to keep the operating
conditions. The noise will be significantly lower when
there is no torque load.

I could do that using a disk (washer) with a radius of about 30% of
the propeller radius (center of mass) and having the same weight as
the four propellers. I think I have some spare props left over from
my last attempt at indoor flying (before I added the shrouds). It's
not a good equivalent load torque because it's not pushing air, but
methinks the inertial load of the disk (washer) will be sufficient to
have the chopper produce some vibrations.

However, I won't have time for a few days. The doctors will be
removing two large kidney stones tomorrow and I may need some time to
recover. To be continued when possible.



Yikes. Best wishes for a speedy recovery--I'll pray for you.


Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

Jeff Liebermann
Guest

Thu Dec 27, 2018 5:45 pm   



On Thu, 27 Dec 2018 02:28:58 -0000 (UTC), John Doe
<always.look_at_message.header> wrote:

Quote:
Jeff Liebermann <jeffl_at_cruzio.com> wrote:
Removing the 300 and 8000Hz tones would probably not have much of
an effect on the overall noise level

Maybe because you can't hear it. It makes a big difference to me.
Shown by pulling my 8 kHz equalizer slider down to zero.


It's possible that I can't hear 8KHz. I haven't tested my hearing in
the last 5 years or so.

>You say "I never guess".

Close. I said: "I never guess when I can also test".
In other words, if there's a way to test my assertions, I prefer doing
that instead of guessing. If that fails, use "the force".

Actually, I do quite a bit of guessing, far more than I consider
acceptable. My favorite excuse is lack of time, which I shall now
invoke as my reason for not testing my hearing or manipulating the
audio track. Besides, it's your problem, not mine, so you should be
doing the experimentation.

Quote:
You might want to start.
Even Blinkin was guessing, and he could at least hear...
https://youtu.be/zJQ7FxLzhVs


Take the recording from the YouTube video and notch out the 8KHz.
Audacity should be suitable for the task:
<https://manual.audacityteam.org/man/notch_filter.html>
Does it now sound acceptable? If so, build a hearing aid or
mechanical headset with a built in 8KHz notch filter, which should
help you fly without irritating noises. Hmmm... I smell a product
idea.


--
Jeff Liebermann jeffl_at_cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Klaus Kragelund
Guest

Thu Dec 27, 2018 6:45 pm   



If the switching frequency is 8kHz, there is of course also harmonics and subharmonics, so just removing the 8kHz from the recording is not a representative figure

Cheers

Klaus

Jeff Liebermann
Guest

Fri Dec 28, 2018 1:45 pm   



On Wed, 26 Dec 2018 22:26:18 -0500, Phil Hobbs
<pcdhSpamMeSenseless_at_electrooptical.net> wrote:

Quote:
On 12/26/18 7:51 PM, Jeff Liebermann wrote:

However, I won't have time for a few days. The doctors will be
removing two large kidney stones tomorrow and I may need some time to
recover. To be continued when possible.

Yikes. Best wishes for a speedy recovery--I'll pray for you.
Cheers
Phil Hobbs


Thank you. I could use all the help I can get. I survived. Left
stone is gone. Right stone is split into tiny rubble, and should pass
when the urologist removes the stents in a week. It's now 4AM on the
left coast and I can't sleep due to pain and having constantly run to
the bathroom. That should diminish sometime tomorrow. I'll
eventually be back to normal, except for my contribution to the
doctor, hospital, anesthesiologist, etc bills.

My apologies for the off topic topic, but it's literally all I can
think of at this time.

--
Jeff Liebermann jeffl_at_cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Jasen Betts
Guest

Sat Dec 29, 2018 4:45 am   



On 2018-12-27, Jeff Liebermann <jeffl_at_cruzio.com> wrote:
Quote:
On Wed, 26 Dec 2018 21:43:53 +0200, Tauno Voipio
tauno.voipio_at_notused.fi.invalid> wrote:

On 26.12.18 20:45, Jeff Liebermann wrote:
On Wed, 26 Dec 2018 11:01:56 -0500, bitrex <user_at_example.net> wrote:

Here's some interesting papers on sources of noise from small DC motors:
https://www.mdpi.com/2072-666X/9/2/84/pdf
http://downloads.hindawi.com/journals/ijrm/2006/063214.pdf
The first seems to indicate a significant source of noise at high freq
in small motors is excited resonance of the motor housing itself

Suggestion: Remove the propellers from the quadcopter and run the
motors without the props. The residual noise should be 100% chopper
noise. I did that in the past on my Walkera XR-350 clone:
http://www.learnbydestroying.com/jeffl/pics/drivel/slides/Walkera%20QR%20X350%20Drone.html
and heard very little remaining noise from the motors. However, my
hearing is not the best, and I didn't bother making any measurements
with an SPL meter. If I find time, I might try it again later today.

If you remove the propellers, you should substitute a
comparable amount of torque load to keep the operating
conditions. The noise will be significantly lower when
there is no torque load.

I could do that using a disk (washer) with a radius of about 30% of
the propeller radius (center of mass) and having the same weight as
the four propellers. I think I have some spare props left over from
my last attempt at indoor flying (before I added the shrouds). It's
not a good equivalent load torque because it's not pushing air, but
methinks the inertial load of the disk (washer) will be sufficient to
have the chopper produce some vibrations.


Props effectively have negative weight in flight. if you're looking for
bearing noise. I guess you can run it upside down with the weights
summing to the craft's normal weight

--
When I tried casting out nines I made a hash of it.

Jasen Betts
Guest

Sat Dec 29, 2018 4:45 am   



On 2018-12-26, Tauno Voipio <tauno.voipio_at_notused.fi.invalid> wrote:
Quote:
On 26.12.18 20:45, Jeff Liebermann wrote:
On Wed, 26 Dec 2018 11:01:56 -0500, bitrex <user_at_example.net> wrote:

Here's some interesting papers on sources of noise from small DC motors:
https://www.mdpi.com/2072-666X/9/2/84/pdf
http://downloads.hindawi.com/journals/ijrm/2006/063214.pdf
The first seems to indicate a significant source of noise at high freq
in small motors is excited resonance of the motor housing itself

Suggestion: Remove the propellers from the quadcopter and run the
motors without the props. The residual noise should be 100% chopper
noise. I did that in the past on my Walkera XR-350 clone:
http://www.learnbydestroying.com/jeffl/pics/drivel/slides/Walkera%20QR%20X350%20Drone.html
and heard very little remaining noise from the motors. However, my
hearing is not the best, and I didn't bother making any measurements
with an SPL meter. If I find time, I might try it again later today.


If you remove the propellers, you should substitute a
comparable amount of torque load to keep the operating
conditions. The noise will be significantly lower when
there is no torque load.


yes, EG. fit an aluminium flywheel with a magnetic brake, or some
other near-silent mechanical load


--
When I tried casting out nines I made a hash of it.

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