FIXED Cromotor v2 RUB, MAGNETS came UNGLUED!

[e-beach]

OK, bent axle question solved...Good looking jig! New side covers with bearings...check....Magnets pushing around....

@zombiess....120*C..? or 248*F......?

that is really a low temperature, I mean unless you are cooking stake or something meaty and you want the fat to drip off. Any good epoxy should take at least double that temperature.

@ Offroader....Can you push all of the magnets around?

 

[Offroader]

Yes I can push all of the magnets around. I take a small allen key and push from the side, and they will move. Some are harder to move than others, probably because of the friction from the magnet next to it, hopefully not because they are demagnetized. I have to push pretty hard for any magnet.

I agree 120c seems to be very low. I would like to know where this number came from as I can push over 120c without any trouble. I seemed to have killed my epoxy by pushing the motor over 150c.

The problem is I notice a cracked magnet, I'll have to get a new magnet. If anyone has an idea where I could find a replacement magnet, please let me know.

The other issue is I wonder how hard it will be to get all those magnets back into the motor. I would think if I left too much space between any magnet, I won't be able to fit the last magnet in the circle. I would have to do a test before I applied any epoxy down.

 

[zombiess]

120c (maybe it was 150) is a number I was told by zelena vozila as a max operating temp. That might be the magnet temp. I don't think I have ever exceeded 135 on a motor. Running things hot reduces their life. Think about hall sensors, they have a max temperature rating and its going to most likely be under 150c.

My setups don't get hot even with +15kw when they are in small diameter wheels. I can't push my 25" setup anywhere near as hard as my 21" setup. Huge difference.

 

[e-beach]

120c (maybe it was 150) is a number I was told by zelena vozila as a max operating temp. ......

120*c equals max operating temperature , that makes more since then max temperature an epoxy can take. Speaking of epoxy, the brave man from the great north used 20 minute epoxy when he redid the magnets in the posted video....call me "Lightning" , but I wouldn't trust myself redoing the whole wheel in just 20 minutes the first time out. I suppose someone could mix some 20 minute epoxy and put some magnets in, then mix some more epoxy and put some more magnets in etc.

On heat, yea it kills a lot of stuff, magnesium as well. Enough heat will weaken your neodymium magnets until they cool down, unless you got them frightfully hot..600*F or so then they loose magnesium.

 

[Offroader]

Just an update, I bought a new cromotor and have my bike up and running. I will not be heating this motor up like I did the last one. I'm even scared about heating it above 100c.

What is the highest I should go without melting the epoxy again? 100c is too easily reached and I want to push a little higher.

My new cromotor is laced into a smaller rim and tire. I must say that I don't think I damaged my old cromotor that much, it still had plenty of power. I know people said I probably demagnetized the magnets. However, its hard to compare because my new cromotor is laced into a smaller wheel so I naturally have more power, but it isn't that much. Of course the new motor doesn't spin the magnets around, which only happened occasionally on my old cromotor.

Suprinsingly, even with the epoxy failed, the magnets won't move that easily. They are stuck on there pretty darn tight. It takes heating the motor up and going up a hill from stop.

I want to fix my old cromotor and I have plenty of time to do it.

The new side covers fixed the rub, so I believe my old covers were possibly warped.

My old cromotor has a magnet that is cracked.

I assume I will need a new magnet. Any ideas on how to acquire a new cromotor magnet?

Once I acquire a few magnets I will remove all the magnets from my cromotor and see if I can put them back. If that works out, I will epoxy them back into the motor.

I will use a very good epoxy, I found this post here on endless sphere recommending this as a good epoxy, stands up to 170c.
http://endless-sphere.com/forums/viewtopic.php?f=16&t=27270

 

[e-beach]

Well........I have never had the time or budget to test the manufactures claims, but this stuff has worked for me in the past. Besides if you have the time, it has the time to dry.

From the manufacturer.

J-B Weld is The Original Cold Weld two-part epoxy system that provides strong, lasting repairs to metal and multiple surfaces. Mixed at a ratio of 1:1, it forms a permanent bond and can be shaped, tapped, filed, sanded and drilled after curing. At room temperature, J-B Weld sets in 20-25 minutes to a dark grey color. A full cure is reached in 15-24 hours. J-B Weld has a tensile strength of 3960 PSI and sets to a hard bond overnight. It can withstand temperatures up to 550ºF when fully cured.

http://www.jbweld.com/product/j-b-weld/

 

[Allex]

If you have temp sensor in the windings then you can easily heat them up to 120°C or even spike to 150°C
But there is really no point to heat your windings up more than 100°C this is because the heat curve is extremly progressive after that.
For axample, when you go WOT(full power) from a cold start you will reach 100°C in 10 minutes, next 100-150°C you will reach within a minute. This is just a axample.
Next, when you windings are at 120°C. This does not mean that your rotor where the magnets are have the same temperature. But if you hold this temperature for a long time the heat will eventually spread to your magnets and then deeper to the Epoxy. Magnets start to loose their power at 80°C and up. When your rotor is at 80, take a brake.

On a normal day, when I hold 120°C on the windings for a long time my rotor is around 75-80°C
So you thump rule should be: try to keep below 100C because of the progression, it's okey to spike to 150°C, keep your rotor cold, below 80°C not for the Epoxy sake but for the magnets

 

[Tench]

Good to hear you have the bike up and running again, the smaller wheel is always a good idea to give a DD hubby an easier life, plus the power benefits make it a no brainer!.
I would be interested to know if you had regen activated when using the motor that failed, and did you do any long decents using regen?

 

[100volts+]

I would be interested to know if you had regen activated

I have a 26 inch wheel and regen set to 70% on a cromotor. I'm going to 19 inch mc wheel and reducing regen to 50%. Don't want to reglue magnets.

I bought a new cromotor and have my bike up and running.

Offroader, I bought a new Cromotor to put in the 19 inch mc wheel. Didn't want my favorite bike down that long in case my lame lacing skills and a miscalculaion in spoke length kept my bike down longer than planned.

 

[Offroader]

Alex, here is where cromotor mounts its temp probe on the v3. It is epoxied just below the windings. Should I consider that temp probe basically on the windings for spike temp?

Actually, that epoxy you see holding the temp probe completely flaked off after I touched it. I'm not sure what they used to epoxy that on but it crumbled like a bread crumb. That was done I believe at the factory in Europe as this is a cromotor v3.

I assume my new cromotor has the temp probe in the same location.

I do not use regen and never had it enabled.

I'll show you exactly what spiked my cromotor above 150c. It was a 90deg day and I drove up these same long stairs. That was when I first heard my magnets rotate in my motor, I don't think I made it completely to the top of the steps.

[youtube]ldY65kUtiBM[/youtube]

 

[e-beach]

.......Actually, that epoxy you see holding the temp probe completely flaked off after I touched it. I'm not sure what they used to epoxy that on but it crumbled like a bread crumb. That was done I believe at the factory in Europe as this is a cromotor v3......

Sounds like a really bad epoxy job, or bad epoxy. No doubt when you put it together again with better epoxy it will hang together longer. Maybe they didn't clean and ruff up all the surfaces before trying to mount stuff. A Monday morning build out of the factory?

 

[Allex]

If you have it on the stator like this, I would not heat this one up more than 100-120°C If you have 120 on the stator your windings are def 150 or more.

 

[gogo]

Just curious, do you have a strategy for preventing side cover damage to your new hubmotor?

 

[Offroader]

Just curious, do you have a strategy for preventing side cover damage to your new hubmotor?

Nothing is conclusive yet about the bent side covers. I am not 100% sure they are bent. Here is what I have to go by.

I did have various degrees of rub and the axle or stator wasn't bent. The degree of rub seemed to change when I removed the old covers and put them on differently. It went from a hard rub to a very soft scrape.

However, when using the new covers the rub seemed to have gone away completely, which makes me believe the old covers were bent. However, the new covers, which were from an old motor had a bad noisy bearing so I need to replace that and put them back on.

What I need to find out is if the stator can pull the magnets off of the motor case and if this is can possibly cause a rub. I will really have to reglue my magnets and then test both covers again.

That being all said, I am not going to beat this new motor like I did the last one. I used to do constant 3 foot drops over and over, hit curbs really hard at fast speeds, when climbing stairs I would come at them at a very high rate of speed which caused the rear tire to hit really hard on the first step. I'm not going to be doing this with the new motor anymore. At least not until I have my eyes on a new and better motor.

If I can fix my old motor I will probably use that as a beater motor and air cool it.

 

[Offroader]

Well........I have never had the time or budget to test the manufactures claims, but this stuff has worked for me in the past. Besides if you have the time, it has the time to dry.

From the manufacturer.

J-B Weld is The Original Cold Weld two-part epoxy system that provides strong, lasting repairs to metal and multiple surfaces. Mixed at a ratio of 1:1, it forms a permanent bond and can be shaped, tapped, filed, sanded and drilled after curing. At room temperature, J-B Weld sets in 20-25 minutes to a dark grey color. A full cure is reached in 15-24 hours. J-B Weld has a tensile strength of 3960 PSI and sets to a hard bond overnight. It can withstand temperatures up to 550ºF when fully cured.

http://www.jbweld.com/product/j-b-weld/

e-beach, I'm trying to look up the specs for JB weld based on tensile strength at different temperatures and can't seem to locate it.

I think that may be the key to finding the best epoxy. The Hysol reported its strength based on the following temperatures.

25c ---- 4200 PSI
82c ---- 3000
93c ---- 2,900
121c ---- 2,300
149c ---- 1600
177c ---- 1200
204c --- 600

You can clearly see as the temperatures rise the bond strength falls pretty fast. JB-Weld only reports its peak bond performance of 3960, but how does it hold up at 150c, or the temps we are likely to see in our motors.

I already burnt the epoxy on my motor due to high temps, I don't want to do it again. I also may consider oil cooling the motor which would put more heat at the magnets.

That one guy recommended the Hysol and seemed to have worked with a lot of epoxies. He never responded to my message, but I wonder why he recommended that stuff.

When I find the Hysol 9394 listed they seem to point out the 177c strength. Makes me think this stuff is good at high temp environments.

I may have sourced some replaceable magnets so I am getting ready to reglue these magnets.

 

[Allex]

You dont have to use epoxy.
I pust my sensor inside the windings, filled empty space with thermal paste and coverd the hole thing with high temp silicone gasket.
It is flexible so everything holds up great. Up to +310 °C
See:
http://endless-sphere.com/forums/viewtopic.php?f=6&t=23996&p=865316&hilit=gasket#p865316

 

[Offroader]

Allex, thanks for the tip and link. I like the thermal paste idea as I was wondering how well it needs to contact the windings.

Does anyone have an idea about how much epoxy I should use to reglue the magnets? Just a thin coating?

How should I prep the surfaces before applying the epoxy.

Just trying to get ideas even if you never reglued magnets. Thanks

 

[alsmith]

Thin. The excess should should squeeze out for you to wipe off. If the epoxy layer was too thick the magnet could hit the rotor.

 

[Offroader]

Thin. The excess should should squeeze out for you to wipe off. If the epoxy layer was too thick the magnet could hit the rotor.

Thanks, should I rough up the surface before applying the epoxy?

 

[alsmith]

Thin. The excess should should squeeze out for you to wipe off. If the epoxy layer was too thick the magnet could hit the rotor.

Thanks, should I rough up the surface before applying the epoxy?

There's usually instructions with the glue, but normally make sure you degrease the mating surfaces and don't touch them after degreasing. Use IPA, denatured alcohol, or similar. I've bought from a drugstore in the past, ebay last time.

 

[Ypedal]

any good solvent with a clean rag/paper towel will work fine... i use rubbing alcohol most of the time, and zippo fluid when it's at arms reach... but yeah, don't contaminate the surfaces once cleaned, even clean fingers leave oily prints.

 

[alsmith]

Get one with no 'extra' ingredients as fragrances or colours can leave a residue to contaminate your joint- everything except denatured or dimineralised water which will evaporate cleanly. It's safest to go for the IPA or alcohol.

 

[Offroader]

Took out all my magnets and put them back in. It went fairly easily. I numbered them all 1 through 46. This was basically a test to see how easily they would go back in before I epoxy them.

I did accidently chip a tiny piece on the bottom corner of one magnet by it being pulled into another magnet. Like ypedal said you have to be careful about them pulling together. They seem far less likely to chip if placing them on metal, but the force of two magnets pulling together will most likely crack or chip them.

What surprised me is the magnets went back in fairly easily and all lined up perfectly. The last one actually had a small gap about .5 mm-.7 mm. I think the magnets self center in the round hub (none seem to be vertical slightly). My theory is the magnets are flat, but they stick best if they are straight in the round hub.

I will make a post after this specifically about this gap.

Here is the motor housing with the magnets out.



Magnets sitting out of the motor



Magnets all back in. #2 is just scratched and not cracked.

 

[Offroader]

A questions I was hoping some of you could answer.

The last magnet went back in with a small gap. It is about .5mm to .7mm. It is a very tiny gap but a gap nevertheless. I didn't epoxy my magnets in just removed the magnets and put them back in.

I didn't notice any shims between my magnets and have no idea why Ypedals motor had them. However, I did notice what looked to be epoxy between a lot of the magnets, or at least that is what I think it was. It was dark grayish in color and felt rubbery and disintegrated easily.

What I think is that maybe when you epoxy the magnets back in some epoxy will get caught between the magnets and this will reduce the size of the gap? Or did the builders of the cromotor purposely put epoxy on the side of the magnets to shim them for some reason? Maybe that rubbery stuff between the magnets was a shim.

I wonder if it is possible that it was just epoxy getting stuck between the magnets as the magnets slides into place picking up excess epoxy from the motor case. And this gap that I found was to leave some room to make sure all the magnets fit back in with obvious epoxy going to get caught between the magnets.

My question is what should I do about this GAP as seen in the picture below, will a gap like this cause problems with the magnetic operation of the motor?

Why did Ypedals motor have shims and Ypedal I believe put those shims back.

THE GAP!

 

[Emoto]

Hi offroader
I would experiment with some custom shims. non magnetic small like 2mm wide then if all good bond a couple of magnets to experiment.
On the broken magnet did you contact zombies/ hal for support ?