FIXED Cromotor v2 RUB, MAGNETS came UNGLUED!

[Spicerack]

Wow you can really see where those magnets were moving around the hub shell! Obviously all the epoxy failed- must be pretty low temp rated! If you had massively overheated your motor, the windings would be dark brown and the strings around the windings burnt, which they aren't.

Just an idea- try sliding a shim of standard copy paper between each magnet and see if that takes up the gap. Realistically I don't think that gap will make much difference at all though. You could also epoxy the broken magnet back in and see how it goes- you might get away with it...

 

[Offroader]

I have magnets being shipped to me right now.

I probably could have reused those chipped magnets, but nothing beats a replacement magnet since I was able to get some.

I don't think the copy paper would work, thinking about it there are 46 magnets. Placing 46 of anything would more than likely fill up the .5mm of space.

I can't chance not having enough room to fit all the magnets when I epoxy everything if the epoxy will get between the magnets and take up space. I just don't know until I do the job.

The more I think about it I think that gap is probably there because a little epoxy is going to get between the magnets. I may try and purposely put some epoxy between the magnets also when I reglue them. A tiny amount on 46 magnets may very well fill that .5mm of space.

I think I'm worrying too much here to be honest. This motor is going to be my beater and possibly experimentation motor when I fix it. Maybe I will try a cooling method on it.

I guess a good thing about all of this is I really learned about the internals of the hubmotor. That was one area I knew nothing about, but now having to deal with this problem I learned a lot.

 

[Emoto]

Obviously all the epoxy failed- must be pretty low temp rated! If you had massively overheated your motor, the windings would be dark brown and the strings around the windings burnt, which they aren't.[/qutte]

Totally, those windings look fine , suspect epoxy or not keyed up properly, then add some heat + vibrations = delmination

 

[Spicerack]

Yeah, I meant three or four bits of copy paper only spread around the circumference... honest! :wink: Totally forgot that there would be 40something bits of paper- that's mm's thick!

The epoxy idea sounds about right. I'd probably mark the position of the magnets so you can see as you go if you're going to be out or not. Good job getting new magnets btw.

 

[alsmith]

A quick google search:
an average sheet of 80gsm paper, the most commonly used weight, measures approximately 0.1mm in thickness, which means that 10 sheets would measure 1mm. By comparison, 10 sheets of 120gsm paper would be 1.5mm thick, assuming the paper composition was the same.

 

[e-beach]

Were there spacers in the the hub to begin with?

 

[Offroader]

Were there spacers in the the hub to begin with?

I didn't notice any. There seemed to be epoxy or something between the magnets. But it wasn't hard it was rubbery and broke apart easily.

Makes me think if epoxy fails does it become brittle and rubbery? Well the temp sensor epoxy flaked off easily, but I thought that was put on in Europe and not where the motors where made in China. I could be wrong here and maybe it was done in china and the same crappy epoxy was used for the temp sensor as for the magnets.

Without putting anything between the magnets I was left with around .5-.7mm space. This is very small for 46 magnets in total. Why would shims be needed anyway?

 

[e-beach]

.....Without putting anything between the magnets I was left with around .5-.7mm space. This is very small for 46 magnets in total. Why would shims be needed anyway?

If all you have left over with all the magnets installed is a maximum of .7mm, then IMO you don't need shims. The epoxy will take up the space. As for crumbling epoxy, I think the stuff the factory used just wasn't up to the job.

 

[Offroader]

I ordered the epoxy. I went with Hysol EA9394. This is really the best stuff I could find. I think it has the strongest strength at higher temps.

The JBWELD may have worked, but I read a review where someone oil cooled his motor and had the epoxy fail, he also used JBWELD . The Hysol EA9394 is made to work with fluids. I may oil-cool this cromotor.

Here is post about his Failing JBWELD while using ATF Fluid.

http://endless-sphere.com/forums/viewtopic.php?p=736797#p736797

Anyway, I ordered 50 grams of Hysol 9394, do you think this will be enough for the job?

 

[crea2k]

The build quality of these motors looks a bit questionable, I took my brand new, never used one apart to get some machining done and one of the hex cover bolts had been snapped off previously by the look of it, then put back in the hole (the rest of the bolt wasnt in the hole, so god knows what was going on there), and another bolt had half of the threads at the bottom cross threaded / mangled to bits. I also noticed that the covers only seem to align the holes right in a certain way, e.g if I spin the cover and just try and do it up with whatever bolt hole with whatever cover hole, some of the other holes then dont line up, and I have to turn the cover one hole at a time until they all line up, which makes you think some tolerances must be a bit off somewhere if something as simple as bolt holes dont even line up, I would think there would be equal spacing between each hole, but by the look of it some are +/- 3-4mm out. Other than that the rest of it appeared to be ok looking inside, not sure why they went with locking nuts for the inside of the freewheel part though, I would have used lugs cast into the cover, wouldn't want one of those nuts flying off inside the motor .

 

[johnrobholmes]

I wouldn't be so fast to attribute the failed epoxy to the quality of things. Remember that both hub shells were cracked, and this would have let the outer rotating part flex. Flexing a ring of magnets will pop them off in a hurry. Just ask my workers that drop motor housings.

 

[zombiess]

This is what a Cromotor looks like that you get it way too hot. This was run in a mid drive setup of a >2000lb vehicle. It was suspected someone left a brake engaged. Windings are fried. I think the power was pretty low too, like 70A at 72V. You can kill any motor when you turn it into a heating element, even with low wattage. I believe the magnet ring is OK, just winding damage.

 

[Offroader]

Just received the replacement magnets and have the epoxy. I'm ready to reglue the magnets any day now.

These magnets are really strong, I had two that squeezed together and pinched the skin on my finger, it wasn't fun trying to get the magnet off using only one hand while it really hurt.

Luckily for me my stator still looks new unlike the one zombiess posted above. I must not have overheated it that much.

I'm interested to find out if the rubbing was caused by the magnets pulling off the motor housing and rubbing the stator or if my side covers are bent. I'm thinking I never bent those side covers and the magnets were being pulled right into the stator. The reason I believe this is I put a wrench on a cracked magnet piece and it pulled right off the motor housing and stuck to the wrench.

Since the coating (probably a nickel coating) that was on the magnets got rubbed off, do I need to protect the magnets with any kind of protecive spraying?

 

[zombiess]

Your magnets most likely came loose from the mechanical interference of the stator hitting them. That sets up vibrations and applies forces at angles to the glue which it weaker. Glue is strongest when the forces its resisting are parallel to the same plane or 90 degrees from the plane.

Think about pulling something apart that is glues together. If you try to slide it apart, or pull it straight off, its difficult. But if you pry up one end you induce an angle that is between 0-90 degrees and its easier. A similar effect can be said for a magnet attracted to something, but with a magnet its often easier to slide it than it is to pull it off when the force is applied 90 degrees to the plane of the flux and the object its attracted to.

 

[Metallover]

I just want to post here, my cromotor magnets came unglued too. I posted about it on my thread here - http://endless-sphere.com/forums/viewtopic.php?p=942734#p942734

I didn't have a temp sensor hooked up at the time- but it did get pretty hot! The windings look brand new; not darkened or black at all.

When I put it all back together, my halls wouldn't work. Both sets. I think they may possibly have rubbed on the magnet chunks that broke off, although they looked fine. I've spent a lot of time troubleshooting.

 

[Offroader]

I just want to post here, my cromotor magnets came unglued too. I posted about it on my thread here - http://endless-sphere.com/forums/viewtopic.php?p=942734#p942734

I didn't have a temp sensor hooked up at the time- but it did get pretty hot! The windings look brand new; not darkened or black at all.

When I put it all back together, my halls wouldn't work. Both sets. I think they may possibly have rubbed on the magnet chunks that broke off, although they looked fine. I've spent a lot of time troubleshooting.

yeah that's what happened with me, I didn't have a temp sensor hooked up. I never realized just how fast these motors heat up. You also have a motorcycle tire on your bike which probably makes the motor heat up even a lot faster.

If you off-road these motors you basically have no choice but to take frequent breaks.

I would consider oil cooling it as when you see how easy it is to heat the motor up with a temp sensor I doubt you're going to like having to take frequent breaks or driving really slow.

 

[Offroader]

Finally got around to regluing the magnets using the Hysol 9394 epoxy. This stuff takes 5 days to cure but it is the best rated for high temp.

I took my time and roughed up the back of each magnet and also roughed up the motor housing so the epoxy sticks better.

I put the motor back together with the original covers in the original position. By rotating the axle with a 10mm wrench I can feel or hear no rubbing now.

So it looks like the side covers never bent and it was most likely just the magnets getting pulled into the stator.

Which makes sense because those side covers are very beefy, I can't see how one could ever bend them.

Nothing is 100% conclusive until In obviously use the motor again and heat it up. But it did rub, before I regaled the magnets, when the motor was cold after multiple tries of putting it back together and even trying different side covers.

You can see a replacement magnet below, which I replaced two cracked ones.

 

[Metallover]

Looks great Offroader!

I want to thow out an update to my re-gluing, with 3M DP460. I got the bike up and running and no issues! I can't tell a difference before or after. Still silent with my adaptto. The cracked magnets seem to be working fine once they got glued back into place. Motor has been up to about 190f with the stock cromotor 10k thermistor.

 

[bigsi]

Any chance you remember the size you ordered? Thanks

 

[Willow]

Any chance you remember the size you ordered? Thanks

...and where you ordered them from??

 

[Offroader]

I think I lucked out in that the cromotor company zelenazoila http://www.zelenavozila.com/ was able to ship me some magnets for I believe the cost of shipping from Ukraine.

I'm not sure how many you need and if he would have extras to do it again.

 

[Willow]

I think I lucked out in that the cromotor company zelenazoila http://www.zelenavozila.com/ was able to ship me some magnets for I believe the cost of shipping from Ukraine.

I'm not sure how many you need and if he would have extras to do it again.

Thanks man, emailed them just before. I screwed up putting the stator back in - didn't go back in straight when the magnets snapped it back in and broke magnets.... need to use the puller and lower it gently back into place.... next time.

sigh.

 

[Offroader]

I think I lucked out in that the cromotor company zelenazoila http://www.zelenavozila.com/ was able to ship me some magnets for I believe the cost of shipping from Ukraine.

I'm not sure how many you need and if he would have extras to do it again.

Thanks man, emailed them just before. I screwed up putting the stator back in - didn't go back in straight when the magnets snapped it back in and broke magnets.... need to use the puller and lower it gently back into place.... next time.

sigh.

That is how I broke mine also, I didn't break it the first time I pulled and installed my stator, but the 2nd or third time I installed the stator when trying to figure out what was causing the rubbing noise I broke some of the magnets. Actually I believe that is how I noticed my magnets were unglued was some of them shifted.

Are any of your magnets loose? Maybe your magnets also came unglued and that is part of the reason they broke so easily.

 

[Willow]

on reflection, I think kit was getting the stator out again that did it.... the axle just clunked the casing a little, thus breaking 2 of t he magnets - they don't look like they could withstand much of an impact... however the third magnet appears to have already been fractured. This is a new, never used Cro, which is getting phase and temp sens. upgrade before use.

 

[ridethelightning]

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