How to stop electrical whining noise?

bitrex <user@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&rsquo;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. 

I hear a steady switching noise, in the neighborhood of 10kHz

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

bitrex
>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

I is most likely
 https://en.wikipedia.org/wiki/Siren_(mythology)
seducing pilots to put their ear next to the propellors
and then have those chopped off.

A classic.

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

Cheers

Klaus

onsdag den 26. december 2018 kl. 10.49.01 UTC+1 skrev Klaus Kragelund:
> 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

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

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

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.

-- 

-TV

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.

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