Magnet adhesive

[mikew8760]

Hi,
The 'noname' 250W bldc motor on my bike seems to have developed an odd fault. Occasionally when under load it loses power and makes a grinding noise for a couple of seconds. My suspicion is that some of the magnets have become loose in some way. I have yet to dismantle it to see if my idea is correct, but if they are loose can anyone suggest a) how to remove them and clean off any old adhesive and b) what sort of adhesive is best for sticking metal to metal?

Thanks in advance.

 

[Benjahmin]

Don't jump the gun Mike ! That could well be a connection fault. Motors that temporarily loose a phase connection or a hall connection will do exactly what you describe. Check all connections going to the motor.

 

[KirstinS]

I would also second the connection fault as most likely suspect

I’ve repaired a few bikes with this symptom that were traced to dodgy connection one way or another

Try hall sensor , phase and then battery connections

Especially if old style jst type


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[mikew8760]

Thanks for the response. I should have said that I have checked and rechecked the usual suspects, and even run it with the controller in Hall-less mode, but makes no difference. My suspicions are partly based on my observation that when I first assembled the bike, I had a look inside the motor, just for curiosity. I thought some of the magnets were not what I'd call 'rigidly' fixed to the rotor, but the adhesive appeared a very slightly rubbery. Not knowing any better I assumed this was correct to fill in the gap between the flat sided magnets and the curvature of the rotor. Now I think that as this compound (cheap Chinese glue? ) gets warm it lets go a bit. It would only need to release a magnet half a millimetre before it would scrape on the stator. I think this might also upset the magnetic field and cause problems.
Perhaps this may be known as a possible failure mode for such motors?

 

[KirstinS]

Thanks for the response. I should have said that I have checked and rechecked the usual suspects, and even run it with the controller in Hall-less mode, but makes no difference. My suspicions are partly based on my observation that when I first assembled the bike, I had a look inside the motor, just for curiosity. I thought some of the magnets were not what I'd call 'rigidly' fixed to the rotor, but the adhesive appeared a very slightly rubbery. Not knowing any better I assumed this was correct to fill in the gap between the flat sided magnets and the curvature of the rotor. Now I think that as this compound (cheap Chinese glue? ) gets warm it lets go a bit. It would only need to release a magnet half a millimetre before it would scrape on the stator. I think this might also upset the magnetic field and cause problems.
Perhaps this may be known as a possible failure mode for such motors?

What you describe would of course be an issue .....but you’d be very unlucky . I don’t recall ever hearing of such a failure in quite a few years of ebiking and forums

My reaction was based on “if you hear hoof beats , think horses not zebra " analogy

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[mikew8760]

Many thanks for the advice from you all, but I'm no further forward. This morning I soldered the joints between the motor phase wires and the controller, just in case the connectors were 'iffy' and the cause of the problem. This has not made any difference!
If the idea of loose rotor magnets may be discounted on the basis of very low probability, that then leaves the controller and the stator windings. I have another controller that I shall try next, but that involves a bit of surgery. Considering the stator windings, is there a simple and effective way of testing them, bearing in mind it only happens under load? I have done static checks for inductance and resistance across two phase windings i.e. green/blue, green/yellow etc and all the readings seem reasonable and the same. It would be impractical to try and ride along even with just a multimeter attached to catch it!
Any bright ideas to shed some light on my predicament most welcome. (Of course, I could just go and buy a new bike, but where's the fun in that?)

 

[Woosh]

you need to check the clutch unit.

 

[KirstinS]

When you say you have checked and rechecked the connections ...have you done a continuity test on the phases and halls ie wiring between controller and motor using a multi meter ? I wonder wether you have an intermittent connection /weak connection due to broken wire somewhere inside the insulation along the length

Certainly you’d get the switch off under load symptom if that’s the case . But then it’s a bugger to find and solve tbh

Re woosh clutch suggestion - they know more than I so


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[mikew8760]

Thanks woosh, but the 'clutch' is not something I had thought would misbehave intermittently under different load conditions. But, by clutch I assume you mean the mechanism to which the 3 planet gears are attached? I'm thinking it's something like a freewheel, and if badly worn or something could sometimes slip? The behaviour certainly sounds very much mechanical, like a short burst of machine gun fire! (Reminds me of the old Sturmey Archer hub gears back in the day!)
And how could it be checked? Replace with a new one, since the one I have seemed to be a sealed unit, that is, all rivetted together. I suspect the chance of finding the correct spare part would be near zero.
Again, more questions than answers.

 

[Woosh]

the clutch looks like this:

Check first for damaged nylon gears.
under load, the one-way bearing may slip. You can test it going up a steep hill.

 

[mikew8760]

Many thanks to all who have given sage advice on my little problem. As a result, and despite a few red herrings, I believe the symptoms I'm experiencing are of a mechanical rather than electrical nature. I've found a couple of entries on the web which describe the result of failure of the so-called 'clutch'. I had looked at the planet gears and not found any worn teeth, so assumed the unit was OK. When the mood takes me I shall dismantle the bike and hub motor (again!) to check this out. I doubt it is in any way repairable, as it's rivetted together, so the final question is - how on earth am I to source a spare part, not having any info. on the motor; all I know is it was on a Power-Cycle wheel.
Again, any suggestions welcome, but it may be the only cure is a new motor?

 

[flecc]

the final question is - how on earth am I to source a spare part, not having any info. on the motor; all I know is it was on a Power-Cycle wheel.

Do you mean Powacycle?

If so, when the need arises, you can contact their support department via this link
.

 

[mikew8760]

Thanks, but I mis-read the label on the wheel rim; it's actually Power Circle, but no further clues...

 

[Woosh]

Thanks, but I mis-read the label on the wheel rim; it's actually Power Circle, but no further clues...

post a few pictures.

 

[flecc]

Thanks, but I mis-read the label on the wheel rim; it's actually Power Circle, but no further clues...

Not one I've ever heard of. If it does turn out to be the freewheel, maybe you could post a couple of photos, the motor before stripping and the freewheel gears assembly. It may be recognised by someone then.

N.B. Crossed with Woosh post above.
.

 

[wheeliepete]

Power Circle is the rim manufacture I think, seen on lots of the cheaper bikes and kits, nothing to do with the motor itself.

 

[Nealh]

T The behaviour certainly sounds very much mechanical, like a short burst of machine gun fire! (Reminds me of the old Sturmey Archer hub gears back in the day!)

The mechanical sound can also be phase wire electrical contact noise often associated with a failing controller if phase wire run is sound. The noise can appear to be mechanical and coming from the hub motor though actually a fault resonating from the controller.

 

[mikew8760]

From above, I suspected the Power Circle related only to the rim. Also, I have another controller I may try out before attacking the hub. A couple of photos for perusal; one is of the Noname hub and second shows the clutch and gears as I was testing it.
Any clues, anyone?

 

[Woosh]

I use a lot of Power Circle's rims, nothing special about them, they are double walled 6061-T6 aluminium alloy rims. The motor is a generic SWXH 250W 120mm motor with 1:4.4 reduction ratio clutch gearbox. You can get replacement motor wheels from ebay, amazon etc.

This thread may be useful to you:
https://endless-sphere.com/forums/viewtopic.php?t=92446

 

[Nealh]

swxh in silver
https://www.greenbikekit.com/bafang-swxh-bldc-hub-engines.html
or black
https://www.greenbikekit.com/8fun-36v-250w-swxh-hub-engine.html

clutch's
https://www.greenbikekit.com/bafang-bldc-hub-motor-clutches.html