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Old Apr 04, 2013, 04:13 PM
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Type of Kevlar to use to hold magnets in place

I am working on an inrunner that has a 4.5" OD by 2.25" stack length rotor. I am trying to find the correct Kevlar thread/yard/tape to use to wrap the rotor in to hold the magnets in place. I know I need an uncoated product for my high temperature epoxy to adhere to. I would just wondering what brand/source do you use.

David
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Old Apr 06, 2013, 05:00 AM
Aka: Tom Jenkins
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Palm Beach County, Fl.
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I have kevlar roving, its easy to pull out a strand and wrap it around something and soak with thin CA..
on the up side if there is clearance you can wrap with spider wire kevlar fishing line
Carbon tow will withstand heat way better, kevlar will melt with a match....
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Old Apr 06, 2013, 08:01 PM
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Quote:
Carbon tow will withstand heat way better, kevlar will melt with a match....
If the motor is getting that hot, you got bigger problems than melted Kevlar
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Old Apr 08, 2013, 12:32 AM
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Originally Posted by C₄H₁₀ View Post
If the motor is getting that hot, you got bigger problems than melted Kevlar
Indeed, like the fact your magnets are not magnetic any-more (in fact they are likely liquid) as are the windings and anything AL (even steel will be getting rather soft, not to mention red hot) .

The middle of a flame from even a match can be well over 1000degC.
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Old Apr 08, 2013, 11:13 AM
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Kevlar or carbon are only secondary in retaining magnets to rotors. The primary retention is the bond between the magnet and the core. Do a bad job on the primary bond and Kevlar or Carbon wrap will just be a waste of time.

FYI CA is just about the worst thing to use in electric motors--it has very poor characteristics when it gets warm.

Steve Neu
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Old Apr 08, 2013, 01:31 PM
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According to Dupont, Kevlar Aramid fiber is rated to 800 to 900 F and does not melt. It decomposes in that temperature range.

The motor I am attempting to rebuild is an Ecycle Solidslot. The magnets were held in place on the rotor by two stainless steel bands (according the manufacturer). I have pulled the magnets and reset them into place. I have plenty of gap space (the stainless bands are 1.5mm thick). I was looking for a source of uncoated Kevlar or carbon fiber yarn to wrap the rotor to replace the stainless bands. Depending on the thickness, I need 40 to 100 yards.

I could by a Kevlar fishing line, that is normally coated to be slick and stop fraying. Epoxy will not bind it properly.
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Old Apr 10, 2013, 03:18 PM
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Are you seriously believing that wrapping the mags with string is going to be a reliable replacement for oem Stainless Steel bands? Yikes!
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Old Apr 10, 2013, 04:03 PM
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How many RC brushless inrunner motor companies wrap their rotors in stainless? I thought carbon fiber or Kevlar is the norm.
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Old Apr 11, 2013, 06:05 AM
Aka: Tom Jenkins
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Quote:
According to Dupont, Kevlar Aramid fiber is rated to 800 to 900 F and does not melt.
What do you call it when it spews Kevlar out like a cotton candy machine at the county fair?
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Old Apr 11, 2013, 09:59 AM
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You either were rubbing or hit a temperature were the resin/epoxy binding the Kevlar/carbon fiber failed.
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Old Apr 11, 2013, 05:03 PM
Aka: Tom Jenkins
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Experimenting with intake/exhaust sizes and got too hot! Believe it or not the windings checked out! It ceased up pretty tight when it cooled
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Old Apr 11, 2013, 07:58 PM
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I gave a hint earlier--the primary magnet retention is from the glue joint between the magnet and rotor core. The Kevlar or carbon really is secondary and will fail to keep the magnets in place if the primary bond fails. The only way to really improve things is by having the carbon or Kevlar tow under a lot of tension when wrapping --which is not easy. A stainless steel sleeve can be very good if you can get a shrink type fit where the stainless tube actually is under tension--again not so easy to do in low cost motors.

Steve
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Old Apr 12, 2013, 12:02 AM
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http://www.thethreadexchange.com/miv...FUOe4Aodf3EAMA
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Old Apr 12, 2013, 03:34 AM
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Good Morning ,
hear what Steve tells you. First find the right glue and second you have to tow the carbon or Kevlar string under high tension. Ther are two ways to do it. 1. to prefabricate a carbontube and slide it with a hydraulic sytem from one side over the rotor .2. to wire a string of carbon or Kevlar under high tow over the rotor and secure the end of the string with this high tension force.Both not easy. And you have to use a Cord/string of carbon or kevlar ,no filament that can not towed with high tension.Alternativ you can also use a Titan wire,that's what we use on our inrunnermotors currently.
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