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How to stop electrical whining noise?

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Lasse Langwadt Christense
Guest

Wed Dec 26, 2018 12:45 pm   



onsdag den 26. december 2018 kl. 10.49.01 UTC+1 skrev Klaus Kragelund:
Quote:
Yes, you can filter it with LC filter

But as I hear it, the high frequency noise is same level as the blade noise, so why bother?

The frequency is low to reduce power switching losses, if you add LC, losses will rise a lot


and possibly mess with the "sensor less" ESC

Klaus Kragelund
Guest

Wed Dec 26, 2018 12:45 pm   



Yes, the filter can only take the brunt of the slope, and no way of knowing how the vector control has been tuned wrt dead times etc


Guest

Wed Dec 26, 2018 12:45 pm   



On Wednesday, 26 December 2018 08:07:53 UTC, bitrex wrote:
Quote:
On 12/26/2018 02:30 AM, 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

Cheers

Klaus


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.


NT

Tauno Voipio
Guest

Wed Dec 26, 2018 3:45 pm   



On 26.12.18 06:02, John Doe wrote:
Quote:
https://youtu.be/FSwZQtqWyHw

Can that whining noise be easily eliminated?

I am assuming its origin is easy for some to guess.
It uses brushless motors controlled by an "electronic speed control"
(ESC). There is a large cap across each ESC supply plus and minus. I
tried adding a 1000 µF low ESR capacitor on the battery input but that
didn't help.

Thanks.



There are sounds in two frequency ranges. The lower frequency
sound comes from the rotor blade tips and it cannot be avoided
as long as you're keeping the thing in the air with the rotors.
The noise is analogous to the whap-whap of a full-size helicopter.

The high-pitch whine comes from the chopper drives to the motors,
and it is most probably from the motor stator magnets. In principle,
it could be avoided by re-designing the motor controls, but the
added weight may render the thing not flyable.

--

-TV


Guest

Wed Dec 26, 2018 4:45 pm   



On Wednesday, December 26, 2018 at 8:51:20 AM UTC-5, Tauno Voipio wrote:
Quote:
On 26.12.18 06:02, John Doe wrote:
https://youtu.be/FSwZQtqWyHw

Can that whining noise be easily eliminated?

I am assuming its origin is easy for some to guess.
It uses brushless motors controlled by an "electronic speed control"
(ESC). There is a large cap across each ESC supply plus and minus. I
tried adding a 1000 µF low ESR capacitor on the battery input but that
didn't help.

Thanks.



There are sounds in two frequency ranges. The lower frequency
sound comes from the rotor blade tips and it cannot be avoided
as long as you're keeping the thing in the air with the rotors.
The noise is analogous to the whap-whap of a full-size helicopter.

The high-pitch whine comes from the chopper drives to the motors,
and it is most probably from the motor stator magnets. In principle,
it could be avoided by re-designing the motor controls, but the
added weight may render the thing not flyable.


Seems to me the solution is to use 1,000 times more rotors turning 100 times slower.


Rick C.

- Get 6 months of free supercharging
- Tesla referral code - https://ts.la/richard11209

Klaus Kragelund
Guest

Wed Dec 26, 2018 5:45 pm   



When we look at motor design, we have the same problems about noise, all though we have solutions by moving above 20kHz

The problem is from modes of the stator. The entire stator is moved in different ways with some being a circular mode, others like an American football in both x and y directions, others like a flower. No way to remove it. Can be reduced by larger teeth and armature, but then no room for copper

bitrex
Guest

Wed Dec 26, 2018 5:45 pm   



On 12/26/2018 11:30 AM, Klaus Kragelund wrote:
Quote:
When we look at motor design, we have the same problems about noise, all though we have solutions by moving above 20kHz

The problem is from modes of the stator. The entire stator is moved in different ways with some being a circular mode, others like an American football in both x and y directions, others like a flower. No way to remove it. Can be reduced by larger teeth and armature, but then no room for copper


Right. If there's no way for the OP to adjust the switching frequency
maybe the only way to improve things is try to damp the interface
between the motors and the airframe, so at least if the airframe itself
can vibrate or has resonant modes around there you're not making the
situation worse

bitrex
Guest

Wed Dec 26, 2018 5:45 pm   



On 12/26/2018 11:30 AM, Klaus Kragelund wrote:
Quote:
When we look at motor design, we have the same problems about noise, all though we have solutions by moving above 20kHz

The problem is from modes of the stator. The entire stator is moved in different ways with some being a circular mode, others like an American football in both x and y directions, others like a flower. No way to remove it. Can be reduced by larger teeth and armature, but then no room for copper


For my part the higher frequency noise isn't what I find objectionable
it's that the blade noise sounds like ten pounds of angry hornets in a
five pound bag!

Tauno Voipio
Guest

Wed Dec 26, 2018 5:45 pm   



On 26.12.18 17:07, gnuarm.deletethisbit_at_gmail.com wrote:
Quote:
On Wednesday, December 26, 2018 at 8:51:20 AM UTC-5, Tauno Voipio wrote:
On 26.12.18 06:02, John Doe wrote:
https://youtu.be/FSwZQtqWyHw

Can that whining noise be easily eliminated?

I am assuming its origin is easy for some to guess.
It uses brushless motors controlled by an "electronic speed control"
(ESC). There is a large cap across each ESC supply plus and minus. I
tried adding a 1000 µF low ESR capacitor on the battery input but that
didn't help.

Thanks.



There are sounds in two frequency ranges. The lower frequency
sound comes from the rotor blade tips and it cannot be avoided
as long as you're keeping the thing in the air with the rotors.
The noise is analogous to the whap-whap of a full-size helicopter.

The high-pitch whine comes from the chopper drives to the motors,
and it is most probably from the motor stator magnets. In principle,
it could be avoided by re-designing the motor controls, but the
added weight may render the thing not flyable.

Seems to me the solution is to use 1,000 times more rotors turning 100 times slower.


Rick C.


Actually, the aerodynamic forces in the sub-sonic range are
proportional to the square of airspeed, so 1000 is not enough
to compensate for a speed reduction by a factor of 100.

A different story is that the efficiency of the rotors decreases
as the number of rotors increases. The effect is the same which
limits just increasing the number of blades in a single rotor.

Your solution aims at the blade noise, but it seems to me that
the OP was more annoyed of the chopper whine from the motor
windings.

--

-TV

bitrex
Guest

Wed Dec 26, 2018 5:45 pm   



On 12/25/2018 11:02 PM, John Doe wrote:
Quote:
https://youtu.be/FSwZQtqWyHw

Can that whining noise be easily eliminated?

I am assuming its origin is easy for some to guess.
It uses brushless motors controlled by an "electronic speed control"
(ESC). There is a large cap across each ESC supply plus and minus. I
tried adding a 1000 µF low ESR capacitor on the battery input but that
didn't help.

Thanks.


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

bitrex
Guest

Wed Dec 26, 2018 5:45 pm   



On 12/26/2018 11:01 AM, bitrex wrote:
Quote:
On 12/25/2018 11:02 PM, John Doe wrote:
https://youtu.be/FSwZQtqWyHw

Can that whining noise be easily eliminated?

I am assuming its origin is easy for some to guess.
It uses brushless motors controlled by an "electronic speed control"
(ESC). There is a large cap across each ESC supply plus and minus. I
tried adding a 1000 µF low ESR capacitor on the battery input but that
didn't help.

Thanks.


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


So maybe try somehow physically dampening the coupling between the
motors and the rest of the airframe

bitrex
Guest

Wed Dec 26, 2018 5:45 pm   



On 12/26/2018 06:20 AM, tabbypurr_at_gmail.com wrote:
Quote:
On Wednesday, 26 December 2018 08:07:53 UTC, bitrex wrote:
On 12/26/2018 02:30 AM, 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

Cheers

Klaus


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.


NT


From the paper I was reading a moment ago small cylindrical motors in
metal housings seem to have a strong vibrational mode at around 7-9kHz,
that corresponds to the motor housing being "squashed" first in the x
direction and then in the y direction in a football-like way, with the
axis of rotation in the Z direction

Jeff Liebermann
Guest

Wed Dec 26, 2018 7:45 pm   



On Wed, 26 Dec 2018 07:42:13 -0000 (UTC), John Doe
<always.look_at_message.header> wrote:

Quote:
Jeff Liebermann <jeffl_at_cruzio.com> wrote:

John Doe <always.look_at_message.header> wrote:

https://youtu.be/FSwZQtqWyHw

The video is from 2005.

The video is from 2015.


Sorry. My mistake. I was wearing the wrong reading glasses.

Quote:
I thought about posting a disclaimer after
clicking Send, but it's not necessary. The video is a concise and
accurate example of the same noise from the same model drone.


It's really hard to not produce noise when you're moving air. Any
turbulence or abrupt pressure change is going to produce some noise.
Actually, the definition of sound is a change in air pressure. To
reduce noise, you can do things with the prop design to ease the
pressure transition, make it less abrupt, or spread it over a larger
area.

"How to Build a Silent Drone - Silent Drone Technology"
<https://fpvdronereviews.com/reviews/silent-drone-technology/>

You might get a clue from the desktop computer case "modding"
movement, which seeks to produce desktops that either don't have any
fans or have very quiet fans. The most common method is to use large
diameter, slowly rotating fans. Most larger case Dell desktops do
this. The really noisy cases do the opposite, with a number of small
diameter, high RPM fans.

If you need some entertainment, find a smoke generator and watch what
happens to the smoke when it goes through your quadcopter turbine
blades. I haven't done this yet, but I suspect that you'll find quite
a bit of air going horizontally, where it contributes nothing to the
lift and just makes noise. Shrouds might help.

Quote:
I already have some third-party props to try. I just need to grind
the nuts for them.


OK. Good luck.

--
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


Guest

Wed Dec 26, 2018 7:45 pm   



bitrex wrote
Quote:
From the paper I was reading a moment ago small cylindrical motors in
metal housings seem to have a strong vibrational mode at around 7-9kHz,
that corresponds to the motor housing being "squashed" first in the x
direction and then in the y direction in a football-like way, with the
axis of rotation in the Z direction


How to reduce motor noise for my Hubsan 501 drone is shown in the video below
Makes a lot of difference it seems.
Never needed for my drone, above 10 to 20 meters you cannot hear it.
https://www.youtube.com/watch?v=gXOTekag-LM

I have read people replace motor bearing too.

There is a lot of user reports and fixes in the Hubsan RC group.
Some motors are noisy some are not..
lots in http://www.rcgroups.com

Jeff Liebermann
Guest

Wed Dec 26, 2018 8:45 pm   



On Wed, 26 Dec 2018 11:01:56 -0500, bitrex <user_at_example.net> wrote:

Quote:
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.

--
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

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