Dismantling and repairing the motor :o

[bob2.0]

Looks tidy.
Think at least twice before gluing the magnets back to the rim, just to make sure that there is a steady alteration of field direction .
It would be a nightmare when you end up with two magnets beneath each other, oriented with the same direction of flux.

They select themselves!

You cannot fit them the wrong way, they will fly off and spin around. They tell you!

Yes, I was very cautious before, you will see I put little dots on after measuring them. It is all nonsense. They go one way and not the other!

I will double check this tomorrow, but it has to be that way because i certainly cannot fit them any other way.

The edges stick to each other, n-s on the top and s-n on the bottom, you see? If you try to put them n-n they just flip around, instantly.

What I did not realise, perhaps it is stupid of me I don't know, I thought the whole rim was aluminum, but the central core is 8mm of solid steel.

So, those magnets grab hold of the field circuit of the magnet next to them that is coming out through the steel surface. That is what holds them in place on the rim, and pulls them hard down to the surface.

I think it is some sort of silver-steel. It does not need to be special magnet steel, it is there to complete the flux circuit and it is what the screw holes for the cover plates are threaded into. Those 24 x M5 screws (12 each side) take the whole load of the back wheel, so I suppose it makes sense to make the magnetic steel element thick enough to also be the load bearer to take those threads

[jeff-jordan]

...
They select themselves!
...
The edges stick to each other, n-s on the top and s-n on the bottom, you see? If you try to put them n-n they just flip around, instantly.
...

Thinking about it a second time, that makes sense .

But how does this affect the 3pack situation? Is it a NSN or SNS 3pack then?

[bob2.0]

how does this affect the 3pack situation? Is it a NSN or SNS 3pack then?

Good question, and I guess I am too hard on myself because that isn't obvious so it was fair for me to mark the magnets so they are right.

Simple answer is I have not tried putting NSN in the 3 pack because I marked them to make sure they were right.

I'll try it today (dry), just out of interest. I suspect the strength of the flux from the surrounding magnets overpowers the repulsion between them, but I don't know.

Maybe I carry on putting marks on the small ones, for now!

[bob2.0]

20 magnets more refreshed and glued in, plus 5 slots of 3pack replacements.

At one point, a batch drifted off the centre line by a few mm because I was so focused on jeff's question about polarity and started doubting myself!

I tried tapping them to see if they'd slide in and were already set enough that I was not going to try too much. With the activator I think they are quite well cured within several minutes.

Total is now 34 slots glued in, 14 to go I have used ~6ml of glue, so a simple calc suggests that is a layer of glue 0.25mm.

In theory, I have enough left in my 10ml bottle. I will try to get it done with what I have.

I have tried to put on just enough that there is a very small amount of excess that just blobs at the edges. Sometimes it hasn't done that (worried if I have used enough), sometimes there is excess I need to wipe up, but for most of the time I seemed to have done OK with the Goldilocks amount of just a small bead of excess around the edges.

Unlike the original manufacture, that's around 'all' the edges, not just one side.

I have developed a method which seems to work well. I don't know how they fit these in the factory. Perhaps they glue them in and then magnetise them?

[bob2.0]

Well, I can say there is no problems with the strength of the glue, except that these magnets are only going to come off as broken bits of rusty dust in the future.

I'll explain my strategy, might be useful to consider if you are in this pickle (though my advice now is to buy another motor!)

See in this image the left most messy slot was a 'key' magnet I left in place, and I removed all the others in the next 7 slots.

I then put a 'spacer' magnet between it and the first one that I glued. I did this to give me more space to sand off that rusty glue so I would not be sanding right up to the edge of a good magnet.

This morning, I removed that rusty slot in the usual way (just tapped it off gently) and in theory the next magnet would just be free to come off.

But, look closely, and there is a little bit of overspill under the corner.

That tiny bit of overspill was enough to hold the magnet firmer and harder than even the best glued magnets I have removed.

The result is that it ripped off a chunk of magnet, clean off!

The ironic part of this is that this magnet was the ONLY magnet I took off that was not rusty at all. So sad!

Well, it is not the only 'I didn't do that, well' issue. It's been a difficult and haphazard job. Rust does not work in a systematic way, every magnet was different in some way and needed slightly different treatment and preparation.

[bob2.0]

Just to explain my logic of what I am nearly completing.

Each quarter of the motor (12 slots) is getting 8 original magnets back, after cleaning and selection, and 4 of those slots will be the new 3 pack magnets.

This means I will have 16 slots with the smaller magnets, up from just the 3 (which I know worked).

Will the motor still work with that many slots with the smaller magnets in?

I don't know. But I had to commit one way or another, once glued on these are no longer ever going to be 'recyclable'.

I hope it works OK. It's become very boring now and I just want my bike back. This will have been a 4 month long repair, including one failed repair. I suppose I should be glad I discovered all this now than the magnets carrying on rusting and becoming beyond refurbishment.

[jeff-jordan]

Over all: tough job!

And I think we all learned a lot from your experience. My appreciation.

I'll keep my fingers crossed that the motor will work without any issues .

[bob2.0]

FWIW and a record of my efforts, the motor now looks like this.

You can see how my plan worked out for locating the smaller magnet sets.

I would have liked to get the alignment better, in hindsight I should have made a simple L-shaped tool to set the distance to the edge of the flange, but I don't think it will have a performance effect . I am more concerned if so many of the smaller magnets are up to the job.

I spent an hour cutting strips of polycarbonate to fit in the gaps (I don't think it is necessary with the strength of the glue, but who can say in the very distant future), but only managed 3 of the 8 I needed, as the gaps are all slightly irregular sizes. Tomorrow I will try heating the polycarbonate until it can deform plastically in to the gap. But one way or another, I will finish the job there.

It took 9ml of my 10ml bottle. I think I used just the right amount, not too much nor too little and I resisted using less as the bottle emptied. There is only just enough now to wet the sides as I turn it upside down! If I wait a long while I can get enough drops out to fix the polycarbonate fillers.

In principle, if the smaller magnets do not work properly, I could try to find/order some exact size ones and chisel those off. But I think simply trying to buy a new motor might be the better answer if that happens. Custom magnets are expensive. For reference, I measured them as 45mm x 16.75mm x 2.5mm.

I suspect the smaller magnets will give me slightly less performance at slow speed but perhaps higher speeds (less back EMF beyond constant V/Hz). This is me being optimistic, I just want my nice bike back on the road!

[bob2.0]

PS If I had known I would end up removing all of the magnets, I would have done 8 pairs of twos, spaced around every 45 degrees. But I had already replaced the 3 rusty ones before the next failures and I did the re-repairs, so I had to match that pattern as those were already glued in place. So it ended up 4 sets at 90 degrees.

I never wanted that much work! I think it has taken me 20, maybe closer to 30 hours, in total, not counting the previous repairs. If your time is worth money then you might want to buy a replacement, but of course it may still have this manufacturing defect with insufficient glue in it.

[bob2.0]

The misaligned 3pack has got me upset.

I'm sad. Those two 3packs on the left were the last two I put in. I guess I was getting tired and a moment's slip up.

The central one is 1.5mm displaced up (in the picture) but it looks worse than it is because the ones on the far left are 1.5mm down.

The left most 3pack is actually in the right place, near enough.

(Also shown are the spacers I've now glued in.)

So, I am a bit sad that I failed to get that part of the job done nicely. I did not see much of an issue at the time, but the poles of the stator are also 45mm, so any misalignment will lead to yet more field weakening of the whole set.

The Hall sensors are ~2.5mm in from the edge, so in theory the field will still be strong enough there to generate the signal. I hope so. The field reverses at the edge of the magnet.

This is a worry because the Hall sensors are about 3mm, and the pole faces are 45mm, the full length of the magnets. That means the very edge of the field will be cutting the Hall sensor, but the field reverses at the edge.

(There is no problem with the side plates,. Magnets normally have a 7.5mm clearance to the surface edge, and the side plates have a 3.5mm depth flange, so normally it is a 4mm gap. My misplacements have now reduced that to 2.5mm in places. )

So, a lesson if anyone were to be foolhardy enough to attempt this themselves, in the future; make a tool to set the magnets spot in the middle.