Motor Noise

[BrushlessinSeattle]

Hi
Excellent forum. Ive followed many of the discussions and Ive learnt a lot.
Im getting ready to build a friction drive system for my road bike.
Initial specs:
Low end torque for hill assist
Light and as quiet as possible.

I live at the top of a 400ft hill and commute to an office which is at sea level. I can get to work without pedaling but could use some help getting home.
I dont care about speed. If I can rig up something that will get me up a 5% gradient at 10mph I'll be thrilled

I would really like to keep the noise level down. Do you guys have any suggestions for how I could minimize noise? Are some RC motors quieter than others?
Perhaps I could build an enclosure for the motor and cool it with a CPU liquid cooling kit (I have one).

I was considering the Hi-Koll (400W) motor which I know from experience is quiet, but I would prefer a motor thats lighter and less bulky.

I'd really appreciate thoughts, ideas, suggestions

Thanks!

 

[AussieJester]

Doubt you will quiet them down a great deal TBH,
watercooling wouldnt be an option on an outrunner and
i'm not convinced it would make it run quieter or cooler for that
matter. The inrunners IMHO is a lil quieter than the outrunners
but both make noise. I have an outrunner myself and LOVE the sound of it
at full throttle, anything below 3/4 throttle though it is very quiet, checkout
this video to
hear the bike at full throttle and below...

If you want something quieter you would need to go with a frock motor (hub motor)
They reckon these are "silent" i have heard two now that made a racket though, apparently the
geared are noisier than the direct drive, the ones i heard where direct drive and far from "silent"

Best of luck...

KiM

 

[BrushlessinSeattle]

Thanks AJ. I watched your vid, cool bike-those belt drives certainly run quiet.
Im still in the design stage. Once I have a plan Ill post some drawings.

 

[olaf-lampe]

I'd say you'd need a big motor for driving silent. Having enough torque at low RPM seems to be the key. The big hub motors are noisy because of the huge sidecovers acting like a resonance-amplifier. The most silent motor would be an outrunner with twisted stator laminations. This seems to make the back emf looking more like a sinus. ( Well, that's my understanding of it anyways )
A few years back, one could buy a DIY motor kit with a set of single stator sheets and make a twisted stator of it. Don't know, if someone is still selling them?
Another way of getting a motor silent is using a sinus waveform controller instead of the common trapezodial shape.
Like www.sinusleistungssteller.de
Mounting the friction-drive motor on rubber feet instead of direct mounting to the bike frame is also helpful.

There is a huge playground to dig out the most silent drive. Go ahead and impress us with your findings
-Olaf

 

[Miles]

The 1800 rpm sensored motor and single stage belt drive on my Moulton is pretty much inaudible.

As Olaf says, sine drives will make a significant difference - let's hope they become more available soon...

The ideal is a motor with sine form BEMF driven by a sine controller.....

 

[BrushlessinSeattle]

Olaf, something like this - right? but configured as an outrunner (coils and magnets reversed).

 

[olaf-lampe]

Olaf, something like this - right? but configured as an outrunner (coils and magnets reversed).

I thought about a smaller twist angle than this one shows. It's a matter of testing or simulating with a finite-element sim.
I've heard of an engineer who adapts a certain kind of PWM pattern to the coils to eliminate noise. Kind of counter-resonant stuff. Works only for a given application/housing. Has to be re-engineered over and over again.
It's a sick world...
Olaf