Brushless Motor Construction Discuss design and construction of custom Brushless motors

Broken Magnets E-Flite Power 60 & 90

Old 06-09-2014, 04:47 PM
  #26  
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Originally Posted by Ohm View Post
Breathing air has proven fatal to everything that breaths it, how bad can a little magnetic dust be?
I really like your tag line.....

"There is nothing so simple it can't be done wrong. "

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Old 06-09-2014, 06:41 PM
  #27  
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I figure after 62 years of woodworking (started when I was 4 yo) and 40 years of being a carpenter, I have at least inhaled an 8'- 4"x 4".

Somehow it seems I got rid of it, a little at a time, just like it came in.

Carpenters are too stupid or proud, to wear a breathing respirator any time, we or someone close to us are cutting wood. Dry wood dust is the worst as it will stay in the air for over an hour. I have seen this in my own shop.

The cup type paper masks are basically useless, unless you duct tape them to your face. WAY too much leakage around the edges. There are some good ones but they are hard to find.

My idea to cut a magnet is to clamp it between 2 strips of wood and then use my wet diamond saw to trim the edge. I have not tried this yet but I think it would work.
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Old 06-09-2014, 07:16 PM
  #28  
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Originally Posted by Wildflyer View Post
I figure after 62 years of woodworking (started when I was 4 yo) and 40 years of being a carpenter, I have at least inhaled an 8'- 4"x 4".

Somehow it seems I got rid of it, a little at a time, just like it came in.

Carpenters are too stupid or proud, to wear a breathing respirator any time, we or someone close to us are cutting wood. Dry wood dust is the worst as it will stay in the air for over an hour. I have seen this in my own shop.

The cup type paper masks are basically useless, unless you duct tape them to your face. WAY too much leakage around the edges. There are some good ones but they are hard to find.

My idea to cut a magnet is to clamp it between 2 strips of wood and then use my wet diamond saw to trim the edge. I have not tried this yet but I think it would work.
Yeah, I also don't have much use for those paper respirators. I've got two of those full face mask rubberized respirators that can use either the charcoal filters, or a very good dust filter. They go for about $25 or so around here. These have one way valves in them for breathing in, and breathing out. Best investment I made for protecting valuable stuff. Having been born and raised on a farm with its usual amount of dust, I use that mask whenever cutting anything around here.

Also found in google that it is not a good idea to cut magnets without the proper equipment. Overheat them, and they loose their magnetism. Magnet dust can ignite, and the fumes from that ignition are poisonous.

One of the magnet supply houses indicates the proper way to cut their magnets is with a diamond saw, along with coolant. Looks like you're all set to go.
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Old 06-10-2014, 03:27 AM
  #29  
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Thanks Denny
Almost any dust can ignite, even steel powder, if it can oxidize it can burn, and of course fumes from any combustion, are poisonous.

My diamond wet saw just seemed like a good idea. I didn't know I was right on.
Now I will have to check out how easy it is to cut a magnet. Probably easier than some tile I have come across.
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Old 06-10-2014, 03:54 PM
  #30  
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NdFeB dust is a health hazard:
en.wikipedia.org/wiki/Neodymium#Precautions

NdFeB magnets get mushy when exposed to moist in the air. Seal them with lacquer/resin/glue:
en.wikipedia.org/wiki/NdFeB#Corrosion_problems

From
www.supermagnete.de/eng/safety_neodymium.php

Originally Posted by www.supermagnete.de
Untreated neodymium magnets oxidise quickly and disintegrate.

Last edited by ron_van_sommeren; 06-10-2014 at 05:49 PM.
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Old 06-12-2014, 05:26 PM
  #31  
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[QUOTE=ron_van_sommeren;950234]NdFeB dust is a health hazard:
en.wikipedia.org/wiki/Neodymium#Precautions

NdFeB magnets get mushy when exposed to moist in the air. Seal them with lacquer/resin/glue:
en.wikipedia.org/wiki/NdFeB#Corrosion_problems

From
www.supermagnete.de/eng/safety_neodymium.php
[/QUOTE

I have read that uncoated magnets deteriorate when uncoated, which makes me wonder because the magnets I replaced in the Park 480 did not have any detectable coating on them. I left the magnets outside in the weather for a month to see what happens to them. hkcm.de offers no coating along with all the other types of coating. The funny thing is uncoated magnets are more expensive than some of the other coatings available. I bought some gold plated magnets a year or so ago because they were the least expensive in the size I was looking for. Although the coating is thin and they say to avoid allot of handling of the magnets as the gold will rub off. They sure do look good when installed.
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Old 06-12-2014, 05:35 PM
  #32  
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Originally Posted by ron_van_sommeren View Post
By going from delta to star you lowered Kv by a factor √3. Kv_delta= √3 Kv_star. Same for torque. And since motorcurrent wants to go up with voltage squared and Kv cubed ...
Thanks for the math, to bad I don't understand it. I got the amps times volt thingy down after that I get confused with all the different symbols different folks use to describe the functions. In the sixty's we had a few old fashion symbols which don't exist on computer key boards. Maybe one of these days I'll take the time to learn what all that means. I think it is really neat to be able to calculate the future. I'm just so ingrained in the monkey see monkey do procedure and having success at it that it makes learning why it works hard to find the time. (translation, means I'm lazy)
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Old 06-12-2014, 05:38 PM
  #33  
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Originally Posted by Wildflyer View Post
Thanks Denny
Almost any dust can ignite, even steel powder, if it can oxidize it can burn, and of course fumes from any combustion, are poisonous.

My diamond wet saw just seemed like a good idea. I didn't know I was right on.
Now I will have to check out how easy it is to cut a magnet. Probably easier than some tile I have come across.
Wet cutting the magnets what a great idea, I think...
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Old 06-13-2014, 06:02 PM
  #34  
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I have to a new blade for my wet saw, as I have totally worn the current one out.

Maybe today I can get there, then we will know.

Thanks for the tips about sealing the magnets, I would not have thought of that.
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Old 06-13-2014, 06:14 PM
  #35  
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Originally Posted by Ohm View Post
Thanks for the math, to bad I don't understand it. I got the amps times volt thingy down after that I get confused with all the different symbols different folks use to describe the functions. In the sixty's we had a few old fashion symbols which don't exist on computer key boards. Maybe one of these days I'll take the time to learn what all that means. I think it is really neat to be able to calculate the future. I'm just so ingrained in the monkey see monkey do procedure and having success at it that it makes learning why it works hard to find the time. (translation, means I'm lazy)
For those who have worked with three phase power, these terms are readily understood.

But, for our use, that Wye and Delta configuration has been decided by the motor mfg when the motor was built. It could be changed afterward, but doing so would be dealing with real short motor magnet wires, and the problems associated with reconnecting them in the different configuration.

I did some of that Wye Delta stuff with those www.gobrushless.com motors I wound up some 10 years ago. (Still have those motors)
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Old 06-13-2014, 06:21 PM
  #36  
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Originally Posted by Ohm View Post
Thanks for the math, to bad I don't understand it....
Kv_delta = 1.75 Kv_star
Kv_star = Kv_delta / 1.75

Double voltage and motor/battery current wants to quadruple (22). An n% increase in voltage will give a 2n% increase in current.
Double Kv and motor/battery current wants to increase by factor 222 = 8! An n% increase in Kv will give a 3n% increase in current.

Last edited by ron_van_sommeren; 06-14-2014 at 06:38 PM.
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Old 06-13-2014, 06:39 PM
  #37  
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Originally Posted by ron_van_sommeren View Post
Kv_delta = 1.75 Kv_star
Kv_star = Kv_star / 1.75

Double voltage and motor/battery current wants to quadruple (22). An n% increase in voltage will give a 2n% increase in current.
Double Kv and motor/battery current wants to increase by factor 222 = 8! An n% increase in Kv will give a 3n% increase in current.

There are a number of very good computer programs that do all the math for you. The one I like is www.motocalc.com.

Another is Drive Calculator.
http://www.drivecalc.de/

Hey, that's an idea for a new thread!
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