Screaming motor...

[Jozzer]

Hello all,
After last weeks blowout of my 408, I rebuilt the motor with the magneto from a 4011 in the casing of the 408. It seems to fit Ok. I took it out for a spin today,(since ther guy building my Puma wheel has still not got it sorted ), and all went well for a while, untill it sttarted making a very loud screaming noise from the hum (like VERY loud brakes squeeling). It makes no noise when peddled, or when the wheel is off the ground and motor applied, but as soon as its back on the floor and I throttle it up at all, it screams again. (No I am NOT running over a small mouse repeatedly ). Looks like the motor will have to come apart again...perhaps it doesn't fit the 408 case very well after all....wondered if anyone had any idea's about what could cause this?
BTW, it seems to be running ok even whilst screaming, though my sense of mechanical sympathy cuts in and I have to release the throttle before I go far enough to be sure :lol:

 

[monster]

lol "sense of mechanical sympathy" like its a real person or something!

 

[Ypedal]

Would you say " High Pitch, barely hear it squeal " vs " Screaming wet V-brakes "

My 406/409 does this high-pitched zzzzzzzz that i can only hear when going thru certain streets when no other cars are present, been doing that since day one, but never been a problem.

And i'm not talking about the Toc-Toc-Toc magnetic pulse, growl, that hub motors make....


:wink:

 

[Jozzer]

Hehe, I've pushed mechanical/electrical things hard over the years, and usually get away with it, even when others don't, because I "feel thier pain" :lol:
No Ypedal, its a real high pitched...and if I rode it down the street my neighbors would call the police Actually, thinking about it, I did feel that the motor went back together a little tight, and also noticed that although the magnet/wall oft he outher casing was dry on the 408, it was well greased on the 4011. I reckon that once it all warmed up, it swelled, and is acting like a big drumbrake. Strange how the noise starts just as soon as the hub starts turning (only under load though...perhaps when the bearings are forced to thier minute tolerance), and doesn't change pitch/volume when the hub increases speed.
nickF told me that most of the noise we hear from these motors is created by the imperfections of the controller output....cant imagine it could make a noise like this though (*remembers something else I read here recently about controllers playing tunes throught he motor*)

 

[fechter]

You might have to take apart the motor and look for signs of rubbing between the magnets or housing and the stator. The machine work on these is not exactly 'German" precision. You might be able to correct it by removing all the side cover screws and rotating the cover a couple of bolt holes, then replace the cover.

Otherwise it could be a bad bearing, but they usually make a clicking sound.

 

[Jozzer]

Ok, I turned the coverplates a little, and put a tiny bit of grease on any surfaces that MIGHT rub. THeres no sign that anything has been rubbing though. It went OK for a mile or so, then started again with a noise...like slipping gears to begin with, then back with the screaming. After letting it cool thouroghly it still makes the noise..
Took a short video so you could see/hear what I meant. The noise doesnt really happen with wheel motion, but with the amount of power fed. the more throttle, the louder.
http://www.youtube.com/watch?v=Xs7Ib8g5aDE

 

[xyster]

Quite the screamer... if it's not a bearing, is it possible to lightly grind the exterior surfaces of the stator a little without compromising anything important?

 

[Ypedal]

ahhhh.. yes.. the screach..

I've had the same thing on my rear dual speed.. but not nearly as LOUD>. yikes.... it went away over time tho.

Does the motor seem harder to turn than usual by hand ?

 

[Ypedal]

Does your controller have a reverse switch ? if so.. try reverse for fun .. ( well.. not while riding mind you.. tho that would make one funny video !! )

 

[TylerDurden]

The frequency of the scream is about 3.1khz.

Anybody know if something in the controller operates at that freq?

 

[oatnet]

The frequency of the scream is about 3.1khz.
Anybody know if something in the controller operates at that freq?

Could it be the 'ghost' of certain departed forum member, muttering something about girl scouts and 'inferior' hub motors? 8) Screaming @ 3.1khz sounds appropriate for the personality.

-JD

 

[Jozzer]

At this point I really do think the noise is controller related....any theories on this? If it were a bearing it would happen under peddle power also. If it were physically rubbing somewhere then more motion would be required before it made the noise...
No reverse switch Buzz...sorry m8, no video fun for you tonight!

 

[The7]

The frequency of the scream is about 3.1khz.

Anybody know if something in the controller operates at that freq?

Ok, let try some mathematics.

Most ebike drive wheel rotate from 400 to 800 rpm at top speed.
Assume 600 rpm.
600 rpm = 10 rev per sec

Most direct drive hub motors have 30 to 5o poles.
Asume 40 poles.

Then frequency of the 3-phase voltage = 10 X40/2 = 200 Hz.

(Some geared motors would work at a higher frequecy)

Only the 15th harmonic of the 200 Hz will give an audiable freq of about 3k Hz.


Most PWM in controllers have switching frequency of 25kHz to 50kHz which you are uable to hear (unless dogs, bats and some other animals).
Only the sub-harmonics of these super-sonic frequency that you may hear (say 1/10 th of 30kHz = 3 kHz)

There is a possibilty that part of the ebike structure is resnonating with these harmonics or sub-harmonics.

 

[TylerDurden]

Then frequency of the 3-phase voltage = 10 X40/2 = 200 Hz.

FWIW, 200hz is the freq indicated in scope shots by Patrick... each hall sensor. (Peukert/powerband topic).