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Oct 22, 2019, 01:56 PM
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I dont really see much point. Are motors not quiet enough already....? Is the already low noise really affecting efficiency ?
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Oct 22, 2019, 03:44 PM
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No FSCW machines are not especially here if it bothers the ops ears and makes his frame resonate. Of course lower thd brings efficiency. Start at the beginning. Slot harmonics are inherent in a fractional slotted concentrated wound machine. (FSCW). There is also promise with single layer (LRK) machines who generate a higher wind factor but more harmonics as well. If those harmonics are removed you will have a more efficient machine that can deliver possible a little more torque.

PowerFactor = cos(\theta_v - \theta_i) \times \sqrt{\frac{1}{1+THD^{2}}}

And it's not always about what an individual needs . Sometimes it's just about pure desire
Last edited by H-1 (1boho); Oct 22, 2019 at 03:55 PM.
Oct 25, 2019, 05:56 AM
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Build a sound chamber out of 1 inch thick MDF lined with convoluted foam and a condenser mic. Make this in a way that allows you to place the motor and drive inside then seal it off. Then run the mic to an RTA. What I continue to conceive is some type of parametric or octave adjustment that would remove everything in the signal but the working and boost it. Another stupid idea that probably wont bring anything but at least you will know for sure what frequencies are boosted while in commutation and if something you do mechanically improves it. You may be able to tackle it from a materials side if there is a place to find its resonant character. Character classified in the way similar to that of say a fiber optic. And I guess you could always build a passive filter with an inductor and cap. A pwm trap as well which I assume is a notch or bandpass. For our motors I don't know physically how large those components would be. In industry they and the reactors are nearly healthy as some of the drives themselves. If they are as big as that its totally out of the question. Electronically ( actively) though, there are several ways.The best bet from here is to look at class D amplifier design for more answers.

Here is a 24db slope butter worth iC.
Last edited by H-1 (1boho); Oct 25, 2019 at 06:20 AM.
Oct 25, 2019, 11:25 PM
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Thread OP
well, so happens I drop some good oil in the motor bearings and what does it sound so quiet now all of a sudden for.

Motor sound is one of those funny things, it's there but hard to explain when logic says it shouldn't be.

hehe, when I'm working on quieting blades and the motor is louder than them, does that suggest anything? It does when all I would do next is build a little cover with some absorptive material lining it, all is well.

Ishould add I did chamfer the trailing edges of the cooling holes on the 3020, that could have also brought a tiny bit of swish sound out, now the blades are about even in loudness.

Interesting because there's been several documents on blades I've been reading since last Saturday and there's a ton to think about in this area that describes some of what sound propagation may look like, but I think I've uncovered a riddle regarding blade sound, the motor sound less disturbing as it used to be, blade sound ever present due to rpm, it is what it is and if I could silence them both, that's another thing for another day, it's late tonight and my head needs a rest.

It is amazing electric motors make sound however.
Last edited by icanflyheli; Oct 25, 2019 at 11:34 PM.
Oct 26, 2019, 12:44 AM
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Sounds like u needed new bearings LOL..... Look at the sikorsky s-97 I think the fastest attack chopper and how they dealt with noisy rigid
counter rotational blades. I still think your best bet is a FC with filter and a compatible drive.
Oct 26, 2019, 01:07 PM
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Thread OP
without saying too much more, there's something in the past week that has clarified where some sound comes from, that it's part of doing business as it were.

It is unknown how much oil could be in a bearing in a motor from the factory but it would have to be assumed it would be less than more. This topic has raised some questions and you've all been very helpful in recognizing some concerns.

A very long time ago I was into taking apart and messing with tiny little Hotwheels sizzlers motors for some dumb reason, you know, how does it go kinds of curious ideas, it was also small hobby motors from Strombecker slot car track cars that caught my attention too.

So here we are some 40+ years later and the gig is brushless, and I like the idea of rebuilding a poor performer into something with better output, that's the game, while learning everything there is to learn. Especially in this day when we have full size autos does the knowledge we reap have a chance to migrate to other areas in life we do not expect, like buying an e car for instance.

Not everyone can entertain the idea of being in a business centered around tech but I don't rule it out. There's a huge amount of money spent by co-operations trying to get the best product out there and often the engineers are happy with something less out of politics or economics. In the hobby world we don't have limitations so the moon is always the goal.

Anyway, some riddles in life are not easily found nor understood clearly, as I have found when speaking to persons who are generally dumb minded, or just misinterpreting everything. In that, I realize that some things are best kept quiet, lol, see where this went? if you had any idea, omg.

A week and a half ago I fashioned a Blue Edge double swept style rotor blade in 700mm while trying to be less obvious by including some different contouring and template. I had to alter it later due to information provided in serious articles on the tech, studies to the effect that a team of 3 German based companies and all their engineers got together to refine the original because they sought to improve it, mine is a good representation of that now, The refinements were focused on several factors of which I took observations from and utilized a little not entirely by choice but by accident. Eventually I'll have to fly a picture somewhere so be patient and wait for it as that was coming soon. My reasons to make some changes were not driven out of the information alone but the info re-enforced my direction to alter my original.

Motor noise? now my 3020 is quiet, not silent which would be ideal. I'll have to go over the electrical cause of motor noise and determine what might be done about it or if it's just the way it is. I may have put too much focus on something really not that concerning, it is what it is as they say.

H-1, I take your advice and direction very seriously, so thanks for the involvement.
Last edited by icanflyheli; Oct 26, 2019 at 01:18 PM.
Oct 29, 2019, 04:25 AM
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You are speaking of Scorpion HK 3020 (Kv 1000 rpm/V, 153g. It so good
Oct 29, 2019, 03:08 PM
An itch?. Scratch build.
eflightray's Avatar
Just came across this thread, so apologies for not reading all the posts, (not that technically minded, just practical).

If you can reduce the 'noise' a brushless motor makes, does it also reduce the sound level of the ESC generated programming 'Beeps' ?

I know the motor acts as the loudspeaker, but what part(s) ?, is it just the windings vibrating that cause the sound ? with he plane acting like a soundboard.

There are sound modules that use transducers instead of loudspeakers for better sound generation using the airframe. But if the motor is also generating the sound that way, should be motor be mounted in soft mounts to reduce the sound transfer.

My interest comes from having an engine sound module fitted in one model, that seem to get drowned out when in flight by the motor 'whine'. I don't think it's bearing or prop related, (it's turning a large prop relatively slowly).

If anyone comes up with a quiet motor it should sell really well among most RC fliers, well at least with those not using noise generating props.

Oct 30, 2019, 01:34 AM
Registered User
The rotor turning is what acts as a loudspeaker. And thanks to Newton's third law, the stator and whatever it's attached to turns the opposite direction. And when jittering back and forth at audio frequency, the rotor has enough inertia to vibrate the airplane.

Once the motor is spinning, expensive ESC's with field-oriented control should be nearly silent, whereas cheap ESC's that cycle through 6 discrete commutation steps will produce some torque ripple which will propagate to the airframe and make noise.

The source of the torque ripple is the distance between the magnetic field produced by the coils and the field from the rotor magnets. With discrete stepping, the rotor magnets pull themselves progressively closer to the active coils, and due to the nature of magnetic fields the pull force increases as they get closer. Then just before they're fully lined up, you switch to the next coil set, which is farther away, so the magnetic pull is weaker.

With field-oriented control, coil sets are pulsed back and forth to create a virtual magnet that moves continuously between them. This way the coil field can be kept the same distance from the rotor magnets at all times, so the torque remains constant.

It should be possible to filter these vibrations out by mounting the motor with a rubber dampener, and probably some rubber washers under the mounting screw heads. When the motor begins to rotate, it will stretch the rubber, and if the direction is reversed before the stretch becomes enough to start transferring torque to the airframe, then the vibration should be contained to the motor.
Oct 30, 2019, 03:03 AM
An itch?. Scratch build.
eflightray's Avatar
Thank you for the explanation.

Oct 30, 2019, 03:44 AM
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Thread OP
so if I hold and spool up a motor in my fingers it's all wind generated noise and bearings I'm hearing?
Oct 30, 2019, 06:59 AM
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Originally Posted by icanflyheli
so if I hold and spool up a motor in my fingers it's all wind generated noise and bearings I'm hearing?
I'm not sure on that one. For the ESC beeping noises, it's probably the fast change of direction that makes a loose motor audible despite having very little surface area. Ears are remarkably sensitive to sharp changes in pressure such as square waves. But it seems unlikely that the torque ripple effect would be strong enough to hear. And it also seems unlikely that bearings and wind would be that loud or make that particular kind of noise. Imagine taking the magnets out so the rotor can turn freely, and spinning it at the same speed. I doubt it would sound the same as a running motor.
Oct 30, 2019, 10:31 AM
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Thread OP
so then is the "wreeee" sound coming from a motor, other than bearings and actual airflow sound from the vents, due to a piston like effect distorting the bell, or the wires? After epoxying the wires the sound from the motor dropped a tiny bit however the esc still rings clear, but is it the esc that's making the beep sounds now? MY esc of interest is a ypg60a.

I've seen a motor bell move slightly when the esc is activated on other helis I own, obviously where the beep sounds come from, so the beep is actually a electronic pulse strong enough to cause sound pressure distortions?

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