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Mar 15, 2003, 10:56 AM
small electrics r BIG FUN
Thread OP

Brushless Motor "De-magnification" ?


I'm familiar with can motors losing power over time due to heat-weakened magnets. Most brushless motors use stronger magnets, but are they still susceptable to de-magnification ?

Do we need to be concerned about our brushless motors running on the warm side ? How warm is acceptable and how warm is too warm for a brushless motor ?

Al
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Mar 15, 2003, 11:17 AM
Rod
Rod
Registered User
Al, Yes we have to be concerned about overheating Brushless motors. I have a friend that has de-magnitised 4 Aveox motors due to overheating them. There were two problems, 1) inadequate cooling vents and exhaust openings, 2) being a Glow flier he tended to forget about using throttle and went full bore for the whole flight, as well as oerproping them.
I use the touch and feel test -- if I can hold my finger on the motor for a slow count fo 3 (seconds), I am OK, otherwise I will reduce the load -- change prop size , open up cooling vents etc. I know this is not very scientific, but I have never fried a motor yet. I am currently looking into getting an infrared temperature gun so that I can get an accurate reading on warm/hot motors. Aveox now has statements on their site about using 140 degree magnets.
Mar 15, 2003, 11:34 AM
small electrics r BIG FUN
Thread OP
Hi Rod

That's just what I needed to hear. I tend to push mine, but I can still hold them after a flight.. So your friend knows the folks at Aveox on a first-name basis ?

Thanks for that informative post !

Al
Mar 15, 2003, 11:51 AM
Registered User
Andy W's Avatar
I demagnitized a brand-new F12 on it's maiden flight!
Controller went to full power and drained my new zapped 12x2400RC pack in a little over a minute. The fuselage (Sirius F5B) was soft when I got it down (prop still spinning at low power)..
Aveox replaced the whole setup (controller failure).
..a
Mar 15, 2003, 12:13 PM
small electrics r BIG FUN
Thread OP
Wow.......What a ride !
Mar 15, 2003, 08:12 PM
Registered User
rcelectfly's Avatar
Aveox now uses high temperature magnets in all of their motors. They are hard to overheat enough to cause their magnets to loose their charge.

Chuck
Mar 15, 2003, 08:35 PM
Registered User
ScottS's Avatar
Actually the aveox magnets have been upgraded from 120 C to 180 C according to the web site. Note this is degrees C not F - 180 C is far hotter than I care to touch.
Mar 15, 2003, 08:36 PM
Registered User
Hi,

Check out the latest Q & EFI (march edition) for a good explaination on exceptable temperatures for brushless motors. Generally the magnets in brushless are rare earth magnets and they can take higher temperatures than a ferrite type can motor. If you are really getting a hot motor after a flight have a look at what prop size you are using and how many batteries you are using. Overproping, using too many cells (go by what is stated by the manufacturer) and throttling too low for too long will result in a hot motor.

Later,
Glen
Mar 16, 2003, 12:01 AM
Registered User
Aviron's Avatar
It's entirely possible to demag a brushless motor. Have done it 3 times without trying too hard...
Mar 16, 2003, 06:17 AM
homo ludens modellisticus
Ron van Sommeren's Avatar
Quote:
Originally posted by Masterpiece
... Generally the magnets in brushless are rare earth magnets and they can take higher temperatures ...
Yes, NdFeB Neodymium. The stronger the magnet's magnetic field (in Tesla), the lower the maximum operating temperature. When gluing magnets in LRK homebuilt outrunner e-motors and curing the glue in an oven, one has to make sure the temperature has stabilised enough (after half an hour) and does not overshoot, otherwise ...

Met vriendelijke groet Ron van Sommeren
LRK homebuilt outrunner e-motor discussion group.
Electric fly-in & lrk meet, June 22nd, 2003, Nijmegen, the Netherlands.


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