RC motors, glue / fill-epoxy between magnets?

[spinningmagnets]

I am hoping that most of the people who have glued between the magnets of their RC motor will post what they have tried here, what worked, what didn't work. Super-glue gel, Devcon, JB-Weld? Pics would be great, too. Thanks in advance!

From reading at the DIY wind-generator website (otherpower.com), I already knew that adding epoxy between the magnets was common. I have been given the impression (unverified yet) that the purpose is to prevent side-to-side vibration of the magnets, which can lead to them coming loose (rather than the holding effect of a glue..). The energized stator tooth pushes the magnet on one side, and also pulls the magnet on its other side at the same time...then after some rotor movement, the forces the magnets feel are reversed.

It may also be valuable for the substance to have some 'give' so it doesn't crack. But what are the limits between too soft (flexible) and too hard (brittle) ? These motors also sometimes get pretty hot, some methods may have better hot characteristics that others.

Here are 3 pics from otherpower.com, and a pic of a stock factory-glue RC-motor from swbluto

 

[Jeremy Harris]

I've filled between the magnets on the outrunners I've used. The way I've done it is to put masking tape around the open end of the bell to make a lip around the inside (to stop the epoxy coming out), then to fill the gaps with epoxy thickened with colloidal silica (which makes it thixotropic so it tend not to run).

I then stick the rotor in the lathe and spin it slowly, whilst warming it gently with a heat gun. This get the epoxy into the gaps between the magnets and gives a nice even thickness. I finish off by boring the epoxy (when it's cured) back until the tool almost touches the magnets, then giving the whole thing a coat of paint (mainly because my motors are going in boats).

So far I'm happy with the results. The motors run more quietly and none have yet failed.

Jeremy

 

[etard]

Wow Jeremy, you must have alot of time on your hands! :lol:

I challenge anybody to top that!

When you say the motor makes less noise, is the because it smooths wind currents inside the motor by being one solid mass instead of all the gaps between the magnets? How much quieter?

Very interesting, yet another reason to own a lathe. :wink:

 

[Jeremy Harris]

I think it's only quieter because the epoxy damps the noise from the can a bit. I think that some of the noise these motors make comes from the can being pulled by each magnetic pulse. As the cans are just fairly thin steel, I think they can flex a bit and work a bit like a loudspeaker (in fact, they make quite good loudspeakers, as anyone who's listened to an RC ESC startup will testify).

Jeremy

 

[Hillhater]

Slipping off topic a little but...
Has anyone yet "programmed" one of these motors play a tune ?.. ( remember the Renault F1 .."we are the champions" )

 

[AussieJester]

I used a two part epoxy on my big Turnigy, nothing as flash as our Mr Harris but
i think it turned out reasonably well... have pushed the motor pretty hard and the
magnets have remained fixed in place

I cut a thin slice of plastic from an old ice cream container lid and used this to apply the epoxy
wiped up the excess with my finger inside a piece of clean cloth.

KiM

 

[spinningmagnets]

Thanks Jeremy and AJ, I appreciate you both taking the time to post your experience and pics.

From Kepler (a busy guy these days!) "...You need to use a high temp epoxy and apply in small stages. Also warm the glue with a heat gun to make it thinner. This way it gets into all the knooks and crannies. Do one or two magnets at the time and let it set until it doesnt run anymore. Takes a few hours to do. dont get too carried away with the amout of glue either as it might put the motor out of balance...I have also used thin super glue when I have wanted to do a quick job. Usein conjunction with some accelerator to stop it running everywhere. Epoxy gives the best results but the superglue is better then nothing..."

From Drifter "...Thanks, I use a lot of epoxy for boat building and there is a glue powder that mixes with the epoxy to make it thicker so it does not run..."

From Doctorbass: "...They should use the 3M scotchweld DP460 epoxy !!! NOTHING IS BETTER THAN THAT!!! 4600psi shear strengh!!! and great endurance at high temp! The DP420 is also excellent.. I personally use that at work for many projects as well as the EC2216 aerospace grade epoxy and it's very tough!!! I rebuilt a broken bionx with that and the magnet will NEVER MOVE again!...if you bake the epoxy to 100 celsius for half an hour it work well and since we push our X5 to 125 celsius on the rotor for many years without to notice any lost of power, I think it's OK ...BTW,the DP460 after it is cured IS EXTREMLY STRONG !!! LIKE STEEL !!! very impressive!!! we did personal shear test on alumimun and we broke the metal instead of the epoxy!

From Karma: "...and mix a few ounces of carbon fiber particles in the resin. double the psi..."

From Markcycle: "...We will be using Loctite 3342 on all future motors..."

From Arlo1: "...When I was looking at the lrk website It said most people used devcon to glue the magnets..."

 

[EVTodd]

I agree with most of that except the comments about gluing in small sections and waiting for each one to dry. Epoxy doesn't stick to dried epoxy worth a darn so in my opinion you're better off doing it all at once.

I personally just slather the stuff in there making sure I get the ends of the magnets too (that's the direction they try to move). Then I just keep turning the can trying to keep it fairly even. After it cures overnight I use an air grinder with a small stone bit to smooth out any raised areas. Oh yeah, don't forget to rough up any surfaces you're going to glue and try to get any old glue off first.

Superglue sucks in this application. I also don't see how people are using any glue that has metal in it. The magnets pull it right off anything you're using to apply it.

 

[AussieJester]

I agree it can be done in one hit no problem at all (well, with the epoxy i used anywayz cant speak for any other adhesives) Also Devcon and JB Weld contain metals it has been spoken about before that this is not a good idea. Devcon maybe available with non metalic substances they do alot of differing metals in it, for other applications its absolutely brilliant i have used it for 20 years myself always have a tube of aluminum impregnated Devcon (well two its 2 part epoxy LoL)

KiM