Learning about RC Motors and striving for quietness.

[Kin]

Hi.

So I'm looking to putting together a e-kickscooter modeled after http://www.evalbum.com/4020, except with lower top end (Maybe 25mph) and a somewhat lower class motor (60 instead of 80?). The thing is, I'd like to address some of the noise problems, and I'm scratching my head at that. By the way, I contacted the guy about the fact I would like to mimic the project, and a summary of his response would be "spread the EV gospel."

By noise problems, I mean, in general I'm trying to minimize the noise. I've been playing around with a crappy electric scooter, an offbrand of the Razor e300, called the R2 Agressor, that I picked up broken from craigslist and restored. It's rather clear that this escooter is too loud, and I want to make something as quiet as reasonably possible. One thing I'm presently considering is- will a belt train be much quieter than a bicycle chain?

Space is insanely tight with this escooter, so I am puzzled by how I might reduce the sound. conceivably I can add some dampening foam all around the motor [a with a little space between], but I dont know how much of an effect that'll have (has anyone tried?)- considering how careful I'll have to be to not allow it to overheat.


So, in summary I guess, can anyone point me in the direction to reducing noise on an escooter build like that? I'm also going to have to figure out how I can up the gear reduction, but, that's a different issue. Here's the most obvious thread I could find while searching ES, http://endless-sphere.com/forums/viewtopic.php?f=28&t=7582#p114370, but it really didn't help that much [perhaps I missed the message].


Thanks everyone/anyone for reading.


To Update:
---I really want to quiet things from the perspective of an outsider.
---Here are some recent questions from the thread (a few posts down):
1) Has anyone tried enclosing their motor with some fan cooling on one side, but otherwise isolated on other sides?
2) Can I use a more powerful motor, and less voltage? Presumably this is going to be a less efficient system, is there any way I can get an idea of how much less efficient? [**I am saying something similar to "Oh, I guess to make it quieter I need to make it more like a hub motor directly driving the system**].
-----> Actually, if anyone could guide me in the direction for understanding voltage and the rotations*voltage factor, then perhaps I could answer this myself. It sounds too simple for me to be saying "Ah, lets just run lower voltage and higher current for the same output at lower RPM."
------> My other thought is that controllers are less efficient at higher current. Is this where the caveat to the above problem is? My demands aren't in the 6kw range, much much lower for this project.

 

[heathyoung]

Any chain drive reduction is going to be loud unfortunatly. Sound insulation is also usually very good heat insulation as well.

 

[Kin]

:/. Hmm. Yeah, I know -I reasoned so much about the sound insulation. I thought there might be a few ways to go around that.

1) I was imagining cells of something that transfers heat well, packed with a sound insulator. So, for example, a small wall made of an array thin pipes that were stuffed with sound/heat insulating foam. :/ seems a bit annoying, though.

2) The other thought is that the geometry of the sound probably matters a lot. For example, I imagine if I sound insulate on top of the top of the motor, and leave the bottom with perhaps even an air-assisted fan cooling, then that could affect the sound of the box entirely differently than if I insulate the bottom and insulate the top. I have no practical nor theoretical knowledge to figure what is the ideal configuration, though, so I figure maybe someone here will know.

My basic assumption is that sound does not radiate in exactly the same way as heat [perhaps more like light]b, moreover, because sound doesnt actually represent that much energy it can be absorbed much more than heat can.


The other point you raise is that "any chain drive reduction is going to be loud unfortunately". Can I assume this means that the majority of the sound is coming from the chain drive, and not some other part of the motor? I can see a situation in which I could cool the motor quite well, while still added a decent amount of foam to the side alongside the drive chain.

[This is a top-down view of only one motor, represented over type lines].

0000000000
0 [Motor]00
||[Motor]000
|||||||||||

0= airflow available
|| = muffling foam.

 

[Kurt]

Not a scooter but I am running a rc motor with belt drive. The drive its self is virtually silent. iIs the out runner motor that makes a lot of noise . It the pitch of the sound that I find most aggravating. I measured it at an average of 85 to at times 100db. Even though wind noise at 30mph can be 85-90db the rc motor pitch makes it aggravating. think angle grinder noise!

The start of this video gives you some idea of the noise. Remember the belt drive is virtualy silent - all the noise is from the motor max 9000rpm.
[youtube]ehN5pbE16o4[/youtube]

 

[MattyCiii]

Maybe the noise cannot be eliminated, but at least it can be controlled.
http://scolton.blogspot.com/2010/12/midi-scooter.html
[youtube]http://www.youtube.com/watch?v=_VabIOYxgM0[/youtube]

Of course the "music" in the video is far more annoying than plain old motor noise, but that is a matter of taste I suppose

 

[Kin]

Haha, , Matt, that was pretty sweet. One of the tracks was something that I haven't heard in a while and I'm trying to remember the name. Oh, well.
The thing is, I'm under the impression the PWM is something that *can* be eliminated, by making it above the audible range.

Not a scooter but I am running a rc motor with belt drive. The drive its self is virtually silent. iIs the out runner motor that makes a lot of noise . It the pitch of the sound that I find most aggravating. I measured it at an average of 85 to at times 100db. Even though wind noise at 30mph can be 85-90db the rc motor pitch makes it aggravating. think angle grinder noise!

Definitively, I understand you there. Even if it was below the wind noise for you, I'd be concerned about the sound being disruptive (in some aesthetic way? People dont seem to mind you zooming around semi-quietly semi-loudly, e.g, if I'm going fast on a boring-bike, but its annoying if someone squeals by them).

So a couple things I gather.
1) It's not necessarily the drive if it's a belt-drive like you have.
2) the RPM matters a lot.


Questions that I have.
1) Have you ever tried seeing how much a piece of soft-cell foam 1inch away from the motor surrounding it on some percentage of its side would dampen the sound? I dont know if it's thermally sustainable for you, but something worth asking

2) Is this thought process clear? Can I use a more powerful motor, and less voltage? Would I even need to use a more powerful motor? Presumably this is going to be a less efficient system, is there any way I can get an idea of how much less efficient? [**I am saying something similar to "Oh, I guess to make it quieter I need to make it more like a hub motor**]. Anythings I need to factor into this?
-----> Actually, if anyone could guide me in the direction for understanding voltage and the rotations*voltage factor, then perhaps I could answer this myself. It sounds too simple for me to be saying "Ah, lets just run lower voltage and higher current for the same output at lower RPM."
------> My other thought is that controllers are less efficient at higher current. Is this where the caveat to the above problem is?

 

[StudEbiker]

Wow Kurt, those are some impressive grades. It's hard to believe you can climb hills like that on 200w.

 

[Kurt]

I did try a slip of automotive car audio sound deadening matting wrapped around the can to try and deaden the ring. it made perhaps 5% difference.I feel running the motor in a unclosed case with fan ducting cooling would be the only real way to do it . At under 2000rpm its not that loud at all.

I have been on some long rides so 50km and had ringing in my ears for days. This has got me concerned. That's why I have switched to a hub motor on this bike.

Wow Kurt, those are some impressive grades. It's hard to believe you can climb hills like that on 200w.

The rc drive climbs hills like no tomorrow !!! That's just around my local streets i have taken it through the national park Hills and it didn't skip a beat. Not 200w though but the 200w sticker works well.

Kurt

 

[AussieJester]

I love the sound of those Turnigys Kurt, yours sounds a lil different to mine
for some reason, my old version one 80-100 sounds different to the
version 2 Turnigy 80-100 130kv motors also, a higher pitch wine
was sweet sweet music i tellz ya haha...If the noise is troubling you though
buy some small ear plugs perhaps? After 25km/hr i can't really hear much of the motor
when i cruise along its at 50-55km/hr hear nothing but wind...

KiM

 

[Kurt]

I agree with you AJ its not that load when you compare it to a gass engine like a 2stroke motor bike.

I think I have another medical issue with my right ear or nerves to my brain that's making it very sensitive to high pitched noise. Just last week A section of steel pipe rolled off my workbench and made a clang -clan- ring noise on the ground and my right ear rang for a long time. I think they call it tinnitus could be nerve damage from all the chromium fumes i breathed in from a decade of SS welding .

I do use earplugs with it now although certain frequency's do damage to your inner ear not through your eardrum but by directly through the bone in your head and then into the middle ear.

one difference with your bike AJ is your running 24 or 26" wheels and fat tyre profiles so you don't need to rev the piss out of your motor to get a good speed. They really start getting loud over 2,000rpm then really loud over 5000rpm.

Perhaps I should just gear mine up a bit more.

Kurt

 

[Kin]

Hmm, I just spent a while trying to figure out more about RC motors. Going through hobbyking does not leave me less confused, though.

I am thinking I'd want a motor between 3-5k on either 12s or 6s [since thats what I have], but that's about all I'm at. Haven't even figured out what gearing I'd need on my tires for 26mph top. Over the weekend I could calculate my torque needs, I suppose.

 

[Miles]

1) Have you ever tried seeing how much a piece of soft-cell foam 1inch away from the motor surrounding it on some percentage of its side would dampen the sound? I dont know if it's thermally sustainable for you, but something worth asking

Foam won't help. To insulate acoustic energy, you need complete enclosure and mass....

 

[Kin]

Yeah. I'm reading about this right now . Two things my build has very little of.

I was also going out on a limb by looking at active noise canceling, which I didnt think would work in an unenclosed space- but, regardless, it seems to be more useful for low frequency, not high.

 

[Thud]

Testing the CA120 last weekend in CA, I was amazed at how quiet that big motor was.

Completely atribital to #1-low rpm's (motor maxed out at 5400rpms) #2- it was solidly mounted to the frame. accelerating, it was quiet as Etards front hub powerd bike.
the chain noise was identical to a pedal bike being cranked at 30+mph.(negligable)

Etards re-wound turnigy on the otherhand has gotten much louder.
Removal of the skirt bearing allows the magnet can to ring like a bell during acceleration. his chain line is slightly louder also with a smaller drive sprocket.

for an ultimate quiet set up. you need to have some sound deading dampeners to stop any possible resonating in the mounting. inside the motor itself is a whole other set of problems. High freq controllers make a lot of noise in the windings themselves while operating.

 

[Kin]

Testing the CA120 last weekend in CA, I was amazed at how quiet that big motor was.

Completely atribital to #1-low rpm's (motor maxed out at 5400rpms) #2- it was solidly mounted to the frame. accelerating, it was quiet as Etards front hub powerd bike.
the chain noise was identical to a pedal bike being cranked at 30+mph.(negligable)

Etards re-wound turnigy on the otherhand has gotten much louder.
Removal of the skirt bearing allows the magnet can to ring like a bell during acceleration. his chain line is slightly louder also with a smaller drive sprocket.

for an ultimate quiet set up. you need to have some sound deading dampeners to stop any possible resonating in the mounting. inside the motor itself is a whole other set of problems. High freq controllers make a lot of noise in the windings themselves while operating.

Am I correct to assume you imply that 'etards rewound turnigy' is of higher max RPM?
I'm going to keep in mine what you say about sound deading dampeners. Some of that is tricky because ultimately the motor needs to be bolted onto the frame, but I think there are ways to add some silicone rubber-like mats to dampen sound.
The upside to after reading that sound "blocking" requires mass and space, there are some items that can do sound-absorbing (like I originally imagined) but I know they're probably a minimal afterthought to first dampening the total sound.

When you say "inside the motor is a whole other set of problems" can you elaborate on them? I know controllers *can* make a lot of noise, but I understand there are ways to make them not make a lot of noise.

This evening I hope to do a lot more reading on the resources thread to understand the theory.

 

[FFR Trikes]

Nice video, Kurt! What controller are you using for 15s?

-Tommy

 

[Kin]

Kurt's bike is (justly) the most popular part of my thread

 

[Kurt]

p Kurt's bike is (justly) the most popular part of my thread

Sorry Kin ... I am 100% with you on the RC noise issue as its what makes it a love hate relationship with my rc drive. At times its enough to make me want to give up on the Rc idea and at times I wouldn't swap it for anything. I will be experimenting with ways to make it more quite for now its soft in ear plugs the + about this method is you dont hear the wind noise. A lot of long distance motorbike riders get special custom moulded plugs. I was thinking about getting a set of studio in ear plugs that are also hedphone's 40db noise protection.

Regarding your battery choice. I would stick with 12s its a good middle ground. Try and keep the motor rpm down as this is a big contributor to noise.The turnigy motors really start to sing at 9,000rpm ..think dremmil tool set to full speed kind of noise.

Tommy,
I am running a stock 12 fet 45A - 48v 9c controller (Its identical to a infineon 12 fet) . It's caps are good for 63v so 15s is my limit.But its doing ok considering its a very mild stock controller and Its good for 2500w.

A Infineon 12, 18 or even 24 fet controller that's been modified from stock with better fets and has some programmability would be a better option for high power. I will most likely end up with a Lyen 18 fet so I can up the amps a little more.

Kurt

 

[AussieJester]

I think if you can get it to at least ~4500watt you will, regretably for me be happier
with the sound :wink: Kurt, will hold you to the 'dibs' on the 80-100 though if you ever sellz him :lol: ..

KiM

p.s Kin, bear in mind the videos of these bikes often amplify the noise, they really aren't that loud
from low to mid range its just WOT they start to sound nice, erm.."noisy"

 

[Dee Jay]

my 2 centavos... what I would do is attach fan blades on RC motor and encase the whole motor in a padded box with slits just wide enough for the belt. This box should have vents that can be openned for better air flow on extemely hot days and nearly completely enlcosed in cool weather. Oh and motor temp sensor would be good

 

[Thud]

to elaborate:
Etards motor has the skirt bearing removed & the outer bearing holder removed form the magnet can...thus it is suported by only by the hub end of the can & resonates noticable at a certain frequency during acceleration....nothing i would ever call stealth.

Inside the motor: the windings in a motor act exactly as windings in a speaker...its what makes the lovely beeps & start up tones that sensorless contorllers use to alert the operator to its status....this comes into play on any controller that does pwm controll....My ca120 motor is fully potted in epoxy & is dramaticly quieter than an un-potted winding. using external halls, you could really hear the squelching of frequency's as i manualy would make timing adjustments...Like an old ham radio sound effect in a cheap movie. it is also my observation sensorless controllers tend to be a bit louder than sensored on the e-bikes.. couldn't begin to explain why.

rpms are definatly a function of adding perccievable sound...the higher frequencys generated by more rpms tend to be more irritating than the lower frequency sounds...A crf450 seems quieter than a 250cc 2 stroke while measuring 20db more on a meter...seems like there was a rubber marketed as "sorbithane" as a shoe incert....I am not certain of the rubber (silicone or other) but we use dampeners to silence & protect our archery equipment.

 

[Kurt]

I am not certain of the rubber (silicone or other) but we use dampeners to silence & protect our archery equipment.

Perhaps that's the answer little rubbery doflickys to take the ring out of it
Kurt

 

[Kurt]

Ok I just went outside and tested both the turnigy 80 - 100 and the bafang motor with DB meter. I took the reading from around 2 feet from both motors. That's about where my head sits on a trike. I did this first test at 40v and ran both motors to WOT. I took video of both tests. 84db for the bafang and 93db for the 80 - 100 .

So the 80-100 is roughly double as loud as a bafang.Not to mention the pitch that is makes it even more perceivably loud.

I will take another test at 60v.I can tell you its going to be a lot louder at 60v, As you can see and hear from the video high RMP is where things start getting loud.

Kurt

Bafang 40v DB
[youtube]PdLBquMs7LY[/youtube]

Turnigy 80-100 40v DB
[youtube]TGp8NnTUDIQ[/youtube]

 

[recumpence]

Bear in mind, sound is related to RPM, motor build style and other things as well.

The Astros are not as loud, and my Plettenberg is really quiet and soothing to listen to. That being said, those are both expensive motors. Keeping RPM down helps alot.

Matt

 

[Kin]

Thanks for all the responses. I'm trying to keep everything in mind. This is great; I appreciate the help as it's my first foray into RC motors. Things are starting to fit into a somewhat clearer picture.