Wheel difficult to turn, blocking point

[Svinkah]

Hi all,

I bought a 1000w 48v a few month ago directly to GM while I was in China and I have now a few time to work on my bike.

But I already have an issue : when I turn the wheel while blocking the axle or the reverse (turning the axle while blocking the wheel), the wheel can turn easily during ~350° but for the las 10°, there is one area which is really difficult to pass through.
I have to force a little (but clearly more than for the rest of the rotation) to pass this point and when I apply enough pressure, it pass this point while making a strange noise.
This noise sound like a metal part was rubbing against another metal part. I have friends who have the same motor and their motors do not make this noise!
The blocking point seems to be always in the same area.

My investigation so far :
- It is not the bearings (I unscrewed both metal parts on each side of the motor and they are turning very smoothly.
- I took care that no phase wire were touching together while doing my tests
- Hall wires seems to be really close to magnets in front of hall's magnets but I don't know if they are touching them when motor is closed (ask me if you need a pic)

Any idea of the origin of this noise and this behaviour of the motor? Could it be a small chip of the machining which could be between the magnets?
Thanks in advance for your help and I apology for my bad english.

Regards,

Sylvain

[Bikemad]

Hi Sylvain andto the forum.

It sounds from your description as if the outer motor ring (the cast iron part lined with magnets) and the stator body (laminated steel former inside the windings) are not quite as concentric as they should be, and the highest point on the stator circumference is rubbing against the closest magnet/s.

I realise this is a new motor, but it could be expensive to send it back and get a replacement under warranty.
If it were mine, I would remove the L/H side cover and carefully withdraw the stator assembly to see exactly where the magnet has been rubbing, and then file/sand down the high spot on the stator to provide some clearance.
I would also apply some paint or grease etc. to the newly exposed bare metal to prevent the stator from rusting.

Alan
 

[Svinkah]

Hi Alan and many thanks for your welcome and your answer.

- Dumb question: which side is L/H side?
Would you have a tutorial for this? I already managed to remove the cover opposite to the cable side, but for the stator, I didn't tried yet.
I found this topic : http://goldenmotor.com/SMF/index.php?topic=1565.msg7808#msg7808 but I wonder if there is a more "industrial" way to do this as I have some tools at home.

- Do you think it will be easy to find the highest point/contact point? Because when once you remove a cover, the stator is no more guided as the axle is "free" because bearings are in those covers. And as it is no more guided, the stator stick to the motor ring because of the magnetic field. Or at least, that's my impression when I remove the cover Am I wrong?

- Another question is for the re-assembly of the motor. Is there a magic solution to put the stator back in the motor ring as the magnetic field should be quite violent? Or do I simply present the stator in front of the motor ring and I just wait the ring stick to the stator and then I try to centre the stator inside the motor ring?

Many thanks for your help and have a good Sunday.
Sylvain

[Svinkah]

Hi again,

So I managed to dismount stator from the motor ring using the good old roots method described on above link

Now I have my stator on one side (I still have the cover on the side were the cable goes out) :


And the motor ring on another side :


I looked carefully on both magnets area of motor ring & stator and nothing was poping to my eyes...
Magnets on motor ring are a bit covered by a white substance but it all magnet are same. I didn't found one point which looks different from the rest. Neither on the stator side...
Any ideas to help me?
If you guys need some specifics pics to help me, don't hesitate to ask!
Thanks in advance for your help
See you,
Sylvain

[Bikemad]

Hi Sylvain, in case you have not already discovered by now, the L/H side is the side with the wires coming out of the axle.

After studying your pictures, I would say that the magnets and stator have definitely been rubbing together.
The front area of the stator in the picture below shows signs of abrasion from contact with the magnets:



And many of the magnets appear to have have surface scratches running in a radial direction around the magnet ring which would also indicate physical contact with the stator:



It looks to me as if the binding is only very slight, so it should only require a gentle bit of sanding on the outer surface of the stator with some 80 grit sandpaper to remove any suspected high spots, and then blow out or vacuum any dust before applying a protective coating of grease or petroleum jelly etc.

While it is apart, I would also lightly clean around the inside of the magnets with some 600 grit wet & dry (used dry) just to remove any surface deposits which may have built up, and then clean thoroughly with a cloth before colouring the surface of the magnets with a permanent marker pen so that any further contact points would be much easier to pinpoint if the motor was still found to be binding slightly after reassembly.

Is there a magic solution to put the stator back in the motor ring as the magnetic field should be quite violent? Or do I simply present the stator in front of the motor ring and I just wait the ring stick to the stator and then I try to centre the stator inside the motor ring?

When refitting the stator assembly into the motor ring, it will be easier if you fit the R/H cover first so that it can be used as a guide for the axle to help centralise the stator.

Place the wheel (with the R/H cover already fitted) flat on the floor using an old piece of carpet, a cushion or thick layer of newspapers etc. to protect the surface of the cover (and your floor) and then hold the wheel down with your knees as you place the stator assembly into position ensuring the axle locates into the bearing. Gradually raise the far side of the wheel off the ground while simultaneously guiding the stator assembly into the motor ring (by holding the exposed end of the axle) until it eventually pops itself into position.

WARNING -Do not put your fingers anywhere near the magnets or the edges of the cover during reassembly as the pull of the magnets on the stator will be very strong!

Make sure the cover is correctly seated before refitting the bolts.

Please let us know whether this successfully cures the binding problem.



Alan
 

[Svinkah]

Hi Alan,

Many thanks for your help.
In fact, the marks you highlighted on the stator are present all around the stator. I'm not sure they appear because of the specific rubbing point because the blocking area is very localised. I wonder if I didn't make those marks during my different attempts when dismounting the stator.
Anyway, I'll do some sanding on the stator side (I fear to sand magnets and damage them and/or remove the surface treatment against corrosion that may exist on them (Nickel plating?))

It's a good idea to put some permanent marker in order to facilitate futur investiguation
Thanks again
I'll keep you inform of the result of all this