Learning about RC Motors and striving for quietness.

[bobc]

My initial impression was that the noise from an RC outrunner was the can itself flexing due to the pull from the stator. If this is the case something like a sorbothane 'o' ring or doughnut, a tight fit on the can should damp it reasonably efffectively. It would have to be tight or it would loosen & fall off when the motor spun up. Maybe a set of ordianry 'o' rings would do it?
There's a noise frequency component from the PWM frequency (which I can't hear any more when it gets over 3 or 4kHz these days..) & one from the magnets moving over the stator poles, which I therefore think is the loud one.
In the industrial drives world it is well known that the noisiest motor drives are the switched reluctance drives - the doubly salient rotor & stator construction flexes the entire housing of the motor as the rotor turns (even BIG industrial ones) to generate the noise - I'm thinking the cheap outrunnrers do a similar thing. I expect the more expensive outrunners (e.g. scorpion) with a thicker magnetic can will flex less & thus be quieter.
On this theory it is reasonable to expect the noise pitch to vary with speed and its intensity to vary with torque loading (i.e. current)

 

[Kurt]

Like I said before I did try wrapping the can in a self adhesive sound deadening matting. Its the kind that is used to line the inside of car doors for Audio deadening and road noise reduction. Surprisingly It made almost no difference to the sound.I feel a lot of the noise is coming from the windings and the frequency and intensity is effected by controller,load, rpm and so on. Sensorless controllers like the rc controllers tend to give the motor a more wizzy turbine sound were sensored controllers give the motor a more notchy sound to them.

Kurt

 

[sn0wchyld]

subbed, I too want to see what can be done to dampen the noise of rc drives, since Im hoping (probably in vain) to start and even finish my d8 rc build over summer... hopefully something like timmas build http://endless-sphere.com/forums/viewtopic.php?f=28&t=23409 only quieter, as I've come to like the little growl from the otherwise silent ht.

What about using brushed motors? flyingmonkey (kiwi member) has had some pretty good success with a motor form http://www.thesuperkids.com/10wabrmofors.html, seems pretty quiet and reliable.

 

[Kin]

subbed, I too want to see what can be done to dampen the noise of rc drives, since Im hoping (probably in vain) to start and even finish my d8 rc build over summer... hopefully something like timmas build http://endless-sphere.com/forums/viewtopic.php?f=28&t=23409 only quieter, as I've come to like the little growl from the otherwise silent ht.

What about using brushed motors? flyingmonkey (kiwi member) has had some pretty good success with a motor form http://www.thesuperkids.com/10wabrmofors.html, seems pretty quiet and reliable.

Hey, unfortunately I haven't done much since the most recent posts on this thread. It's only a few pages long now (worth reading everything), but some of the main points are 1) low RPM 3-5k 2) Belt drive 3) Need to figure out some way to get the vibrations of the thin-metal RC motor cans to be dampened. In a way, this amounts to saying "the way to get RC motors quieter is to get them more and more like geared hubmotors.

About the Brushed motors, just wondering, what makes you think they would be quieter? I am under the impression that the early brushed motors were substantially louder even than the HK RC motors, though some of that may be their early generation as opposed to the intrinsic nature of brushed motors. I know the Schwinn S1000 / Ezip1000 is quieter by running a direct gear (nochain or belt) system.

 

[sn0wchyld]

subbed, I too want to see what can be done to dampen the noise of rc drives, since Im hoping (probably in vain) to start and even finish my d8 rc build over summer... hopefully something like timmas build http://endless-sphere.com/forums/viewtopic.php?f=28&t=23409 only quieter, as I've come to like the little growl from the otherwise silent ht.

What about using brushed motors? flyingmonkey (kiwi member) has had some pretty good success with a motor form http://www.thesuperkids.com/10wabrmofors.html, seems pretty quiet and reliable.

Hey, unfortunately I haven't done much since the most recent posts on this thread. It's only a few pages long now (worth reading everything), but some of the main points are 1) low RPM 3-5k 2) Belt drive 3) Need to figure out some way to get the vibrations of the thin-metal RC motor cans to be dampened. In a way, this amounts to saying "the way to get RC motors quieter is to get them more and more like geared hubmotors.

About the Brushed motors, just wondering, what makes you think they would be quieter? I am under the impression that the early brushed motors were substantially louder even than the HK RC motors, though some of that may be their early generation as opposed to the intrinsic nature of brushed motors. I know the Schwinn S1000 / Ezip1000 is quieter by running a direct gear (nochain or belt) system.

Like you I thought brushed = noisy. but allot of em run at lower rmps, and after seeing some vids of flyingmonkeys build they seem fairly quiet... or at least 'less loud'. http://endless-sphere.com/forums/viewtopic.php?f=28&t=19841&start=180#p411960 gives you an idea.

 

[bobc]

Just a thought regarding the magnetic forces on the stator (can) of a brushed motor - they are 1) constant and 2) stationary.

 

[Warren]

"the way to get RC motors quieter is to get them more and more like geared hubmotors."

I worked for a company back in the '80's that made a machine which used a screaming router motor. We tried the various foams, and egg carton shapes. What is needed to dampen high pitched noise is mass, like lead sheet.

 

[Kin]

Just a thought regarding the magnetic forces on the stator (can) of a brushed motor - they are 1) constant and 2) stationary.

Ok, that is a fair point, but I'm not sure it's enough to make too many conclusions.

"the way to get RC motors quieter is to get them more and more like geared hubmotors."

I worked for a company back in the '80's that made a machine which used a screaming router motor. We tried the various foams, and egg carton shapes. What is needed to dampen high pitched noise is mass, like lead sheet.

So in context I guess I mean that "some of the reasons for which we use the RC motors are also directly related to their noise." Power/kg ratio is related to the vibration of the thin-metal cans, Gear reduction sound related to the high RPM efficiency. Etc. A good example of my off-hand hubmotors comment is that Schwinn S1000 "stealth" electric kick-scooter. It's still noisy, but it's a direct gearing drive so as to stop any chain/belt noise.

Here's my question about the lead information. Is it the *mass* that matters, or the density? If it's entirely just the mass, then sound-blocking seems to be out of the window. I doubt many people are interested in adding a lot of weight. Not knowing much about sound isolation, I wonder if the density is a factor (in a sense, that the higher density would reflect sound without allowing it to resonate). If thats the case, perhaps we could find a medium weight lead sheet that could also offer quality blocking.

From what I have read about noise isolation is that there are two principles- sound blocking and sound absorption. Sound blocking uses a variety of materials, traditionally lead-related but now not necessarily so much lead, to simply block the sound. Sound is the property of some materials to be more likely to absorb the energy of the sound waves. Sound absorption is probably what I'm most interested n, but have a few caveats 1) The same properties tend to be very good thermal insulators 2) Apparently it' doesn't do that much.

 

[Kurt]

Here is another way of looking at it regarding the pitch of the RC sound. Get yourself a little battery operated smoke alarm. Set the alarm off by pushing the test button and try and block the noise. this is the extreme end but you will soon get the idea of how hard it is to block high pitch noises.

You will notice that other than locking it in a sealed dense box not much will work. Its not that its that hard to eliminate the sound from a motor its more the nature of a a rc motor that needs air to breath-cooling and access to output shaft, belts power wires. Not to mention the outer can has to spin to. This all makes it extremely difficult.

Good in ear earplugs would be the best solution .

Spin your Rc motor at DD hub motor speed say 300rpm- 1000rpm and its just as quiet


Kurt

 

[Miles]

You need a material with the highest density coupled with the least rigidity. That's why lead is good. Mass loaded vinyl is used as a practical solution. High frequency noise is the easiest to attenuate....

 

[Kin]

You need a material with the highest density coupled with the least rigidity. That's why lead is good. Mass loaded vinyl is used as a practical solution. High frequency noise is the easiest to attenuate....

Hi Miles. I have read about this [as sound-blocking], but it remains that it's unclear whether some mass-loaded vinyl would be sufficient for our needs without having to make it too heavy/thick. I don't know how it plays out in our real-world conditions. I've also never found decibel reduction ratings to really reflect a real-world situation since they refer only amplitude while our ears vary their interpretations based on pitch and number of pitches. Further, the motor tends to be mounted directly to a metal frame that will likely resonate the vibrations even if everywhere else we use this vinyl to cover the surroundings of the motor. I'm curious if anyone has had success. I liked your explanation of highest density +least rigidity makes a decent amount of success as a parameter that lends to low resonance.

Here is another way of looking at it regarding the pitch of the RC sound. Get yourself a little battery operated smoke alarm. Set the alarm off by pushing the test button and try and block the noise. this is the extreme end but you will soon get the idea of how hard it is to block high pitch noises.

This can actually be a little misleading, because our ears are more sensitive to high pitch sounds. If you put yourself in front of a X watt (let's say, 10watt) speaker pumping a high pitch sound- yes, it will sound louder than a 10 watt speaker pumping a low pitch sound. BUT, if you are then to put on jackhammer earmuffs or shotgun earmuffs, it's very possible that the low pitch will sound lower, because the headphones are much better at absorbing high pitch sounds than low pitch sounds.

You will notice that other than locking it in a sealed dense box not much will work. Its not that its that hard to eliminate the sound from a motor its more the nature of a a rc motor that needs air to breath-cooling and access to output shaft, belts power wires. Not to mention the outer can has to spin to. This all makes it extremely difficult.

Yeah, this is the biggest struggle. :S Nothing about the nature of RC motors tends itself to low sound

Good in ear earplugs would be the best solution .

Alas, my concern is for bystanders; its not too loud for me as the rider.

Spin your Rc motor at DD hub motor speed say 300rpm- 1000rpm and its just as quiet

I suppose this is my end approach and what it seems come down to. Except I wont be able to get really close to that low, if only because I'm using 8" wheels for the scooter, but I can do a 1/2 ratio and approach something half-decent. Hopefully.