DD hub Magnets rubbing Stator after adding Statorade

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hias9

1 kW
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Jul 11, 2018
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On a 3000W 45mm magnet height hub motor I added some Statorade. Now the magnets seem to rub on the stator.

I took a little video of it: https://files.fm/u/bnfztptnn

I marked the sidecovers before and installed them the same way like they were installed before.

I already tried using different sidecovers, replacing the bearings, removing shaft seals and adding/removing bearing spacers. Nothing helped.
I can only say for sure that it is not the windings rubbing on a sidecover, so it seems to be the magnets rubbing on the stator.

Without the wheel installed, when turning the axle with a 10mm wrench it is barely hearable when turning the axle very slowly, but clearly hearable when turning the axle faster.

Does anybody have an idea what could solve this?
 
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If it's the magnets rubbing, there will be marks on the magnets and the stator from it fairly quickly. That will show you the "high spot" on the stator, meaning the location where the rotor is getting too close to it.

Whenever I've seen this happen after motor disassembly, it has always been because of a side-cover reinstallation issue. If you've eliminated that, I'm not sure what else to look at, except:

If the magnets are not well-secured to the rotor, and one or more of them has come unglued, it could be displaced while the stator is in place (but not visibly so without it), and rubbing on the stator. If this is the case, only that magnet will have a mark on it from the stator (the stator mark may actually go all teh way around).
 
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Today I checked again. No loose magnets. The marks on the stator on one side are between center and left, on the opposite side between center and right. So the stator sits like this inside the rotor (exagerated of course):

I also verified that by drilling a hole in on of the sidecovers. If I turn the stator by 180 degrees, it moves about 0.5mm to the left/right at the spot of the sidecover hole.

Here is a picture where you can see some of the marks on the stator:
 
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hias9 said:
Today I checked again. No loose magnets. The marks on the stator on one side are between center and left, on the opposite side between center and right. So the stator sits like this inside the rotor (exagerated of course):
Click to expand...
That probably means that the bearings in the side covers are no longer sitting flat in the covers, perpendicular to the cover / rotor plane. This can be fixed by placing the side cover outer side down on a hard surface (concrete, etc) and use a rubber mallet to gently but firmly tap the *outer* race of the bearings (not the inner one!) down flush into the bearing hole in the cover. If the mallet can't reach the race, you can use something else like a large nut drive socket that is the same OD as the outer race to press on the race as you tap with the mallet. (if you hit the inner race or the bearings/seal, you may damage the bearing and have to replace it).

Or, it means the axle in the stator is not perpendicular to the stator plane. This is less likely because it should take a lot more force to create this situation if it didn't exist before, and is more likley to break things when it happens in a way you could see (cracked stator/axle supports, separate of stator from supports, etc).

Or it means there were spacers between the bearings and the stator axle shoulder inboard of them, that are no longer present, allowing the rotor to shift around on the axle laterally. (probably not, because this isn't the same behavior you describe below)


I also verified that by drilling a hole in on of the sidecovers. If I turn the stator by 180 degrees, it moves about 0.5mm to the left/right at the spot of the sidecover hole.
Click to expand...

By "turn the stator", do you mean rotating the wheel (which actually turns the rotor, which is the magnets/etc)?

Or do you mean taking the stator out and flipping it around and reinstalling it in the rotor so the axle end that was pointed toward you is now pointed away?


Here is a picture where you can see some of the marks on the stator:
Click to expand...


If those marks are from magnets, there will be corresponding marks on the magnets themselves. If there are not, then those marks are more likely from manufacturing or handling at some point.
 
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By "turning the stator" I mean turning the axle with a 10mm wrench which is like turning the wheel when the wheel is installed.

As already mentioned in the first post, to fix this issue I have already replaced the bearings and tried different combinations with the bearing washers (orignally it had 3x0.2mm, I used to run 1x0.5mm before; if I use 1mm, the windings on the left side touch the inside of the sidecover). Nothing helped.
I also tried with different sidecovers (so also with different bearings). The bearings sit all the way inside. They are not hard to install when heating up the sidecover before installing. If I need to push them down I use large sockets that fit the outer race and a hammer.

The axle sits tight inside the stator and there is no damage.

The stator is new (I had it rewinded for more copper fill). I only did a test ride with cooling fins before, but without Statorade.
The marks cannot be from manufacturing because this stator has never been inside a rotor before and the marks were not there before I installed it. Also the marks match what I see through the hole I have now drilled into one sidecover.
Everything was fine. The only thing I changed now was adding the Statorade.
The rotor is older and the magnets have some marks.
 
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By the way, what exactly is the reason why there is sometimes the stator rubbing on the magnets if reinstalling the sidecovers in a different way?
How do they know at the factory in which way they need to be installed?
I reinstalled them the same way like they were installed, but also have this rubbing.
 
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I doubt the Statorade itself did anything to cause this.

For sure double check the spoke tension and make sure it's even. I had a DD motor start rubbing when the spokes got uneven.
 
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Yes, I already thought of that and trued the rim a bit. Also checked with a tensiometer. Spoke tension was quite high (I reduced it a bit now), but I am only using butted 13/14ga spokes and guess the force on the rotor would usually be higher when using 10/12ga spokes. Also there are the cooling fins between the spoke flanges. Loosening them did not help.
 
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Not really. It did not change at all with trueing the rim. I trued the rim (not the rotor. If spoke tension would be exactly equal everywhere, the rim would not be trued. However spoke tension is pretty much equal at the moment) after the rubbing started (which was when I added the Statorade).

If that would be the reason why its rubbing it would be quite strange because I guess the force of 10/12ga spokes pulling on the rotor would usually be higher than the force of my butted 13/14ga spokes.
 
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The rotor needs not only to be round (not egg shaped) but also concentric with the axle or you will quickly run into envelope issues with something like this. Not sure if you can put a dial indicator on a machined part of the rotor that parallels the magnet mounting surface to see what you now have. The ones I have played with have had some clearance with the side covers so some concentricity and roundness issues could easily creep in from less than super careful reassembly never mind messing with the spoke tension. You suggested some spokes had too much tension. Wondering if you had a gauge - measurement number in pounds or kg or just going by feel.
 
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The marks in the pic would be elongated it doesnt take much to mark up the lamination some even take a flat head screw driver to the cover plate and go a little too deep
 
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speedmd said:
The rotor needs not only to be round (not egg shaped) but also concentric with the axle or you will quickly run into envelope issues with something like this. Not sure if you can put a dial indicator on a machined part of the rotor that parallels the magnet mounting surface to see what you now have. The ones I have played with have had some clearance with the side covers so some concentricity and roundness issues could easily creep in from less than super careful reassembly never mind messing with the spoke tension. You suggested some spokes had too much tension. Wondering if you had a gauge - measurement number in pounds or kg or just going by feel.
Click to expand...
As already mentioned I measured spoke tension with a tensiometer.

I never ever used a flat head screwdriver for disassembly, but always a 3-arm gear puller.
 
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I measured spoke tension with a tensiometer.
Click to expand...

Wondering how many KG was on them and what was the range of readings. If they varied more than 30% or so and you then removed the motor side covers, I could see it mess things up in a big way. I don't think ferrofluid would or even could have anything to do with it.
 
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Yes, tension was quite high. About 1100-1400N.
30% variance is not much. If you need much dishing offset, variance between the left and right side will already be higher than that.
In this case there is not much variance because I don't need much dishing offset und put ellbows in on one side and ellbows out on the other side.
And this motor is designed for thicker 10/12ga spokes. I guess tension would be way higher when it would be laced into a motorcycle rim with 10ga spokes.
 
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Same side variance. The dish side will be significantly lower. 1100 is good if your rim can take it. Much lower and the dish side will be relatively slack and weak. Still would try to get a indicator on the rotor some way. From your sketch of the stator, it looks like the stator is not perpendicular to the axle or the axle or stator may be bent in some way. Is that what your showing?
 
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The rim is a strong DH rim and can take way more than 1100N.

The stator is perpendicular to the axle and the axle is not bent.
Problem is on the rotor/sidecover part, not on the stator/axle part.

The problem is that the stator seems to be sitting inside the rotor like in the drawing (of course it's much exaggerated).
 
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Are you able to take some accurate measurements? That would most likely help zero in on the roundness, runout and squareness of the interfering parts and spot what exactly is causing the issue. IMO You may want to change the tile of the thread also as nothing so far can be rationally attributed to statorade.
 
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At the moment unfortunately not.
Well, the only thing I changed was adding the Statorade.
I pressed the stator about 40mm to one side (with a 3-arm gear puller), then added the Statorade to the magnets, then slowly let the stator go back to it's final position (aligned with the magnets). The strange thing was that even after removing the gear puller completely, the stator was still a few millimeters away from it's final position.
This is strange because I never had this before. So it could really be an issue with rotor roundness.
I then had to pull on the axle which braught it in its final position, but some milliliters of Statorade squirted outside of the motor. I added a few milliliters after that.
 
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Just look what I wrote in my post right above yours one hour ago.
I always remove the side covers when adding Statorade because it will slightly leak at high rpm when not using silicone.
 
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