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Old 04-18-2013, 05:21 AM   #1
kavic5150
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Post Replacement outrunner motor magnets

I just bought a used z-power Z50a-600 (565kv) motor. One of the magnets was cracked and I decided to replace all 10 of them.

They are flat, rectangular magnets measuring 30mm x 8mm x 1.5mm

The magnet supplier is asking me how I want them magnetized, through the length, width or thickness of the magnet. They also want to know what strength magnets I need.

Can anyone help me out with this? Should I tackle this job myself? What type of glue should I use?

The magnets seem to have very little glue. There are slots at the top of the can which they fit snugly into and I was able to remove one of them rather easily.

Thanks in advance.
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Old 04-18-2013, 10:10 AM   #2
Airworks
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mmmmm , well from tinkering with cans after destroying amotor and pulling the magnets out , i dont see it being an easy task man. they fight each otehr through the process and thiers jigs they use to secure them in the glue curing process, also alignment (i see you said slots of some sort). that might help but , i still dont see this being easy to do,

as far as magnet s, i'd think the most powerful they can get them , no clue on direction or anything, i'd think lenghtwise down the thin center/front back???? jsut guessing.

glue would have to withstand heat , some sorta high temp epoxy?

i tried using a good brand epoxy once but didnt hold very long with a magnet that let go ina can on me before.
and trust me , it was only 1 magnet , and took forever trying to figure out how to keep it in proper placement without the crazy jigs they use.
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Old 04-18-2013, 10:17 AM   #3
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Default Replacement outrunner motor magnets

Sorry but you are really going to struggle IMO...

They will be hard to remove, hard to glue in place without a jig and after all that you'll still probably have a hard time balancing it and getting it to run smooth.
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Old 04-18-2013, 11:36 AM   #4
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As far as removing magnets, that of course "depends" on what glue the motor manufacturer used. At least for one motor I had, the magnets all came loose after I soaked the can (not the stator!) in a small jar of acetone. It dissolved the glue. But your milage may vary.

Regarding magnets to buy, you need to consider two things--magnet strength and heat sensitivity. Of course it is important to get the dimensions right, since clearance with the stator will depend on the thickness and width. Length is as long as the original so the motor goes back together. I'd recommend checking out what Scorpion uses, because I think they at least give an approximate rating for theirs--it helps you to figure out what you want.

I have used two glues in past work. One is the rubberized CA which I think you can get from Gobrushless.com (at least you can get the glue type there. Here you put coat the bottom of the magnet with the stuff and slide in.

I have also used JBWeld. There I first put in a very thin coating on the can, the a very thin coating on the bottom of the magnet. The I slid the magnet it. These magnets were curved, so you tend to scrape off the glue. After all magnets were in, I put the shaft in my drill press and spun the can. Then with a heat gun (hair drier would be ok) I lightly warmed up the spinning can so the JBWeld could flow a bit around the magnets. Anyway this worked.

With flat magnets you have a bigger gap between the bottom of the magnet and the curved can. You might be able to get away with medium CA dribbled down both the center and the sides of the magnets. Try not to go overboard because eventually too much will pool at the bottom of the can, assuming you are holding the can vertically.

I also recommend cleaning both the can and magnets with alcohol or acetone to remove any crud that might be on them.
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Old 04-18-2013, 02:43 PM   #5
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In my opinion, without doing the job properly and having the right materials, you are looking for failure and a destroyed heli. I personally would rather just buy a new motor than to chance destroying my heli. Before attempting a task, I always ask myself if this is a feasible fix.
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Old 04-18-2013, 05:05 PM   #6
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I was planning on sending the motor out to get fixed. The problem I'm forseeing is how to accurately balance the magnet can.
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Old 04-18-2013, 07:16 PM   #7
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Quote:
Originally Posted by kavic5150 View Post
I was planning on sending the motor out to get fixed. The problem I'm forseeing is how to accurately balance the magnet can.
That will cost more than buying a new one...
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Old 04-19-2013, 05:28 AM   #8
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I'm planning to go forward with motor repairs.

Fairly certain the magnets are polarized through their thickness. Then it dawned on me that all I have to do is yank 2 of them to check.

Thanks Ahahn for the tip on scorpion motors. I dug up an old thread on the topic, heres an excerpt.

NdFeB magnets are available in several different compositions with varying max temperature ranges. These temperature ranges are signified by a letter code after the strength value. Here is a list of the ones that are currently available, along with the max temp.

80C - No suffix

100C - M

120C - H

150C - SH

180C - UH

200C - EH

The entire part number of a magnet normally started with a letter "N" to signify that it is a NdFeB magnet, which is then followed by the magnet strength, and finally the temperature rating. So common magnet part numbers would be N48, N45M, N42H, N35UH N30EH and so on.

Typically, as the magnet strength goes up, the max operating temperature goes down, so you end up with the following magnet strength-temp ranges being commonly available.

The "No Suffix" magnets, which are rated for 80C (176F) are available in the N48 to N50 range.

The "M" magnets, rated at 100C (212F) are available in the N45-N48 range.

The "H" magnets, rated at 120C (248F) are available in the N42-N48 range.

The "SH" magnets, rated at 150C (302F) are available in the N38-N42 range.

The "UH" magnets, rated at 180C (356F) are available in the N30-N35 range

And the "EH" magnets, rated at 200C (392F) are available in the N28-N33 range.

Now with that understanding about the magnets, I can move on to explaining the magnets used in our motors. As I stated earlier, most of the better motor manufacturere are using N50 or N48M magnets in their motors. Using an N48M magnet give you a motor that can withstand 20C more temperature, ann still have 96% of the magnetic strength of an N50 magnet, so it is a good trade-off. For cost reasons, the majority of the cheap Chinese No-name import motors use N35 or N38 magnets in either 80C or 100C temperature ratings.

http://www.rcgroups.com/forums/showthread.php?t=660918&page=3


Based on this, I'm thinking somewhere in the H range. I did send an email to Dan@GoBrushless.com asking about this topic. Waiting to hear back from him.
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Old 06-24-2014, 10:30 PM   #9
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Found some on ebay.

http://www.ebay.com/itm/111371470501...84.m1439.l2649

It turns out I had measured wrong before with the ruler. The calipers say 2mm exactly.

I guess I'll have to buy a 700 size heli now that I'll have a motor for one.
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Old 06-25-2014, 12:50 PM   #10
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Quote:
Originally Posted by kavic5150 View Post
Found some on ebay.

http://www.ebay.com/itm/111371470501...84.m1439.l2649

It turns out I had measured wrong before with the ruler. The calipers say 2mm exactly.

I guess I'll have to buy a 700 size heli now that I'll have a motor for one.
Hum...
Risk a 700 with a tricky job you never did before?
Maybe shorting the motor and causing a fire on-board?

It's your call, of course, but try to balance the risk+expense/proffit.
I really think there is no formula for it, but the result is quite often: get a new one
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Old 06-25-2014, 02:25 PM   #11
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Money you spent might be more than buying another used one. Hopefully better luck this time.
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