Dismantling and repairing the motor :o

[bob2.0]

The magnets I will use for the repair;

This is what 'fake' magnets look like;

You can immediately tell these are weak magnets because they do not even have spacers. If they were full strength for neodymium, they would need spacers or you would probably brake them when separating or bringing them together. (The squares came with spacers!)

[jeff-jordan]

Yeah, unfortunately there are some black sheeps under these sellers.
Good that you've had your flux meter, so you could deliver concrete evidence.

But not only Chinese vendors sell junk.
I recently bought 2 disc drives (to repair my nephews PS4 slim) through amazon. Both arrived here with signs of wear and simply didn't work at all.
Thanks to prime, sending them back and getting full refund was no problem. Luckily I was able to repair the genuine disc drive itself...

Hope your loctite stuff arrives soon.

[bob2.0]

Today, I took the other magnet off that was showing damage.

I thought you might like to see progress.

There are a few interesting points to notice.

I removed the other plate on the rim, and so I could see the other side of the magnets.

Here is the other damaged one.

See how there is that little tell-tale triangle. The flux probe showed that the field had been lost here (it actually showed a reverse field, as the flux would pass into it rather than come out of it, if you understand?).

The plating of the edge must have become damaged, rusted, then the magnet swells and pushes into the path of the stator.

I was more gentle this time, and because the magnet was not rusted (weakened), it came off in one piece.

I measured the surface flux on the good end, and it said 0.12T, so I measured the new magnet is stronger than this one!


Here is the gaps now shown for both of the magnets to be replaced.

I did some initial cleaning, I will do more before gluing in the new magnets.

The first thing to see is how the glue is fixed. There is no glue in the middle of the magnet. They have saved glue by only putting it down the edges. I don't think this is a short cut, because it is a flat magnet onto a curved rim (a chord of a circle) so there would be a small gap.

It is this small gap that my small screwdriver fitted behind, so a gentle tapping releases the magnet.

There is no drama. They are not thick magnets. It is not too different to removing a strong fridge magnet. I have seen people express fear at removing these, but there is no issue at all. Easy.

In fact it came off too easily, in my opinion. But we do not hear of these falling off very often, so I guess it does not need much.

I will be using structural adhesive, so, possibly, mine will be a stronger magnet than production, and also glued in more strongly too!

See also, on that one magnet left in the middle, the laminations have been very slightly touching it, leaving those lines. It is possible the corrosion of those two others has already infected this one, and it is also rusting from behind?

[jeff-jordan]

...
I thought you might like to see progress.
...
(it actually showed a reverse field...)

Yes, keep us up to date!
About the direction of the field: shouldn't it alter every magnet:... N S N S N S ... and so on?

[bob2.0]

About the direction of the field: shouldn't it alter every magnet:... N S N S N S ... and so on?

I meant it showed a negative flux in the vicinity of the 'V', while the rest of the face was positive flux. It was making a field loop back into itself.

I don't think that helps the motor work well!

I'll show you a picture later.

[jeff-jordan]

Ah, now I understood.
Yeah, this behaviour of the damaged magnet doesn't improve the motors performance.

[bob2.0]

I was thinking about the bad plating on the other magnets.

You might have seen there is even a chip in the magnet next to the new hole? It is where a piece of rust fell out.

How to cover up all the damaged plating?

I cannot decide.

Something that tries to stop moisture might only trap it?

I was thinking of putting a layer of epoxy over bad plating?

Or use lanoline which stays semi-mobile and let humidity out (like on rusty cars).

We talked about this before and I was going to use some automatic transmission fluid, just a film.

But this needs more. Something to help the plating of the bad magnets.

Clear paint (suggested), maybe. Epoxy? Lanoline? I don't know. Maybe just the oil and open it up next year and check everything?

[jeff-jordan]

...
Or use lanoline which stays semi-mobile and let humidity out (like on rusty cars).
...
We talked about this before and I was going to use some automatic transmission fluid, just a film.
...

I would just go for a thin film of oil (transmission fluid).
Ok, lanoline melts at about 44 °C. What do you get then: organic oil with a low melting point that might char.

[bob2.0]

I glued them on.

I think?

They slid around on a film of glue. I hope that did not mean the layer of glue becomes too thin.

They repel each other in this sort of situation (all one pole is towards us, so the layers repel) and create a 2mm gap between each other if not held, so I used strong tape to hold them in place.

I will wait 24 hours and see what the result is.

I have no idea how I can test the bond strength. If there is any way I can do that?

[bob2.0]

I was busy in the month, so just left the wheel in my house for the glue to cure for a week or two.

I have just put the wheel back together now.

I did not find it to be an easy job, I could not figure out the best way to get the bearings back into place. I think the best way would be to use a semi-circular tool, like a seal hammer, hold it to the centre flange, and hammer it home. But I do not have one.

Apart from reseating the bearings, it was OK the way I did it.

It rotates freely, and the cogging torque feels normal when I short the phases. So I think it is OK.

I will check everything tomorrow and retorque the flanges fully, once the sealant has cured.

I don't think it is an easy design to assemble accurately or easily. I can't see easy machine assembly, I think it is a lot of labour. I guess labour is cheap in China?