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#1 havlicek

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Posted 23 April 2018 - 05:20 AM

     It seems as though with some winds, especially fast small gauge ones where the wire is so tight and close (like G12...50/29), extra attention is in order to make sure the epoxy has FULLY penetrated the coils.  I had one of these very high-timed arms run great until the outer layer of some of the coils started lifting, which caused the arm to slow down.  Large wire, just by it's very nature tends to leave more space for the epoxy to work it's way into.  Small wire, #30, #31 winds tend to not be so fast that this becomes a problem.  50/29 on a .440" stack with 40+ degrees advance is a pretty smokin' hot arm, and doing that wind on a .560" diameter blank makes for a super-tight 4 layer coil...and I DO yank on that wire when winding.

     So I backed-off on the tension just a bit, went to a different wind pattern (*still a 4 layer coil, but with one less turn on the first layer) that I think will allow for better penetration, and most importantly made a significant change in how I epoxy that I'll stay with for all armatures.  I thought about this for a while and after trying it, I *think* I got significantly better results with the epoxy.  It sure seems as though noticeably more epoxy was absorbed by the coils than I usually see.  Failure is the only way to move forward is the way I see it.  :D

     Again, this arm will go into a C can ceramic setup with the magnets honed-out to .580"

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#2 Rob Voska

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Posted 23 April 2018 - 06:13 AM

When winding an arm do you clean the stack, wire, and everything before startign so the epoxy has the best chance?  Is there a way to thin the epoxy for better penetration?


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#3 Jaeger Team

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Posted 23 April 2018 - 06:24 AM

did you warm up before epoxying or/and which is the trick ?


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#4 havlicek

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Posted 23 April 2018 - 06:48 AM

Hi Guys,

 

 

When winding an arm do you clean the stack, wire, and everything before startign so the epoxy has the best chance?  Is there a way to thin the epoxy for better penetration?

Everything always gets cleaned before winding, including the com and com tabs.  That sort of thing is basic to all this and something I've been vary careful about since the beginning.  The epoxy I use is very "thin" by nature Rob, and while there are solvents that will thin this and other epoxies, they all will degrade the epoxy's strength and hardness as far as I know.  Years ago when I built surfboards, we would slightly thin out the final "gloss" coat, but also add a cobalt ingredient that would counteract the thinner and help make that coat very hard so it could be polished-out to a high gloss.  Then again, those boards all used a polyester resin.  Today, many (not all) surfboards use an epoxy resin, but not all get a high-polish.  

 

 

did you warm up before epoxying or/and which is the trick ?

 

I ALWAYS warm the arm before epoxying to around 200F or a little more.  This substantially thins-out the already thin epoxy even more...to almost a "water-thin" consistency.  It becomes so thin that you REALLY have to be careful to not get the epoxy running all over the com or the tail end of the stack.

Here, I've changed the epoxying sequence and technique, not the prep at all, but there's still the possibility of the epoxy running where you don't want it to.

***It's possible with thinner gauge wire to get the coils so tight and compact that you can make it difficult for even such thin material as this epoxy to penetrate, but much more so with #28, #29 wire because of how closely the layers fit over each other and the wire turns fit against each other.  This has forced me to look deeper into how I apply the epoxy.  The irony here is that sloppy coils are MUCH more absorbent because by nature there are a lot of spaces in them for the epoxy to get into.  The trick here still, is to get enough epoxy to fully penetrate very tight coils, but not so much as to wind up with the old "coke bottle" epoxy jobs of the 1960's. :)


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#5 Jaeger Team

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Posted 23 April 2018 - 07:19 AM

What about a micro hyperbaric chamber ?


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#6 wbugenis

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Posted 23 April 2018 - 08:00 AM

All my observations indicate epoxy penetration is not the issue.  I have cut open John's arms and my own

 

(using a different epoxy)  that died in testing and have always seen epoxy all the way to the core of the armature blank.

 

I have used both vacuum impregnation and (the easier) heating the arm to 200 degrees  - both produce identical results -

 

the desired epoxy penetration to the core of the blank.

 

What Dave P. did to that arm to get the coil to lift was  pretty extreme but that is what Dave does.

 

I think he mentioned he was in record territory before the motor slowed.

 

I would look to the epoxy itself that may have softened although Monty Ohren used this Duralco Epoxy for years

 

without an issue I am aware of.  


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#7 Geary Carrier

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Posted 23 April 2018 - 09:37 AM


Here, I've changed the epoxying sequence and technique, not the prep at all, but there's still the possibility of the epoxy running where you don't want it to.

 

 

Hi John,

 

How is the new sequence and technique performed as opposed to the old?

 

 

Thanks,

g


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#8 Geary Carrier

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Posted 23 April 2018 - 09:41 AM

All my observations indicate epoxy penetration is not the issue.  I have cut open John's arms and my own

 

(using a different epoxy)  that died in testing and have always seen epoxy all the way to the core of the armature blank.

 

 

Hi Bill,

 

What was the different epoxy that you mention here?

 

 

Thanks,

g


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#9 gotboostedvr6

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Posted 23 April 2018 - 09:46 AM

I'll tear it down now and report on the epoxy depth. Or uh.. penetration hehe
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#10 gotboostedvr6

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Posted 23 April 2018 - 10:05 AM

Penetration great.

Epoxy/cure time temp ect, looks like the issue.Screenshot_2018-04-23-11-03-35.png
Freedom is never more than one generation away from extinction. We didn't pass it to our children in the bloodstream. It must be fought for, protected, and handed on for them to do the same, or one day we will spend our sunset years telling our children and our children's children what it was once like in the United States where men were free. - Ronald Regan #40 (1911 - 2004)

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#11 gotboostedvr6

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Posted 23 April 2018 - 10:06 AM

Arm dye is the correct color so I doubt overheat was the cause. Didn't require any heat to remove wire.

Now stop distracting me so I can focus on mounting diamond abrasives on wornout hudy drums :)
Freedom is never more than one generation away from extinction. We didn't pass it to our children in the bloodstream. It must be fought for, protected, and handed on for them to do the same, or one day we will spend our sunset years telling our children and our children's children what it was once like in the United States where men were free. - Ronald Regan #40 (1911 - 2004)

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#12 Tim Neja

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Posted 23 April 2018 - 11:02 AM

What about baking the arms in a vacuum chamber?  That would allow ultimate penetration for the epoxy!   When we build planes with foam core wings--we put them in a vacuum to "pull" the balsa skins onto the wing surface! It ensures a good bond.


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#13 tonyp

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Posted 23 April 2018 - 11:45 AM

We would epoxy our RC arms and pit in Vacuum chamber then bake them.


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#14 havlicek

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Posted 23 April 2018 - 01:38 PM

 

Hi John,

 

How is the new sequence and technique performed as opposed to the old?

 

 

Thanks,

g

 

 

Hi Geary,

     Well, since this is all pretty much by hand and feel, I hesitate to try and give instructions.  As per above, I've not had difficulty getting the epoxy to fully penetrate the coils before, but now I think I'm getting more of it in there.  It could also be that it's time for a new batch of Duralco 4461.  I keep it refrigerated to prolong the life of the stuff, but it may be past it's prime???


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#15 Rob Voska

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Posted 23 April 2018 - 02:02 PM

Because of EPA regs..... make sure the new stuff is as good as the old stuff.



#16 havlicek

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Posted 23 April 2018 - 02:39 PM

Because of EPA regs..... make sure the new stuff is as good as the old stuff.

 

I'm confident the formula for 4461 hasn't changed.  Just to be sure and to rule out the material being past it's prime, I just ordered a new batch.  I've never come close to using the whole "Pint Trial Kit".  It's amazing that you can do hundreds of arms and only make it a little more than half way through such a small amount.


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#17 Jaeger Team

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Posted 23 April 2018 - 02:39 PM

All my observations indicate epoxy penetration is not the issue.  I have cut open John's arms and my own

 

(using a different epoxy)  that died in testing and have always seen epoxy all the way to the core of the armature blank.

 

I have used both vacuum impregnation and (the easier) heating the arm to 200 degrees  - both produce identical results -

 

the desired epoxy penetration to the core of the blank.

 

What Dave P. did to that arm to get the coil to lift was  pretty extreme but that is what Dave does.

 

I think he mentioned he was in record territory before the motor slowed.

 

I would look to the epoxy itself that may have softened although Monty Ohren used this Duralco Epoxy for years

 

without an issue I am aware of.  

 

 

Penetration great.

Epoxy/cure time temp ect, looks like the issue.attachicon.gifScreenshot_2018-04-23-11-03-35.png

Sometimes epoxy shelf life could be the issue


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#18 Geary Carrier

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Posted 23 April 2018 - 03:11 PM

 

 

Hi Geary,

     Well, since this is all pretty much by hand and feel, I hesitate to try and give instructions.  As per above, I've not had difficulty getting the epoxy to fully penetrate the coils before, but now I think I'm getting more of it in there.  It could also be that it's time for a new batch of Duralco 4461.  I keep it refrigerated to prolong the life of the stuff, but it may be past it's prime???

 

Thanks John, I can appreciate that...


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#19 Champion 507

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Posted 27 April 2018 - 05:38 PM

Just ordered a new batch of 4461. $138.01 incl shipping. Ouch. They don't give that stuff away. And I haven't even received it yet.


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#20 Geary Carrier

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Posted 27 April 2018 - 06:37 PM

Just ordered a new batch of 4461. $138.01 incl shipping. Ouch. They don't give that stuff away. And I haven't even received it yet.

 

Doug you done good...

 

check out the 250gm size and it ain't as good as 4461 by a long shot above 180C

http://epoxymarket.c...ductDescription


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#21 wbugenis

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Posted 27 April 2018 - 07:02 PM

The Duralco should work for just about anything we would want to do.

 

Otherwise look for (google) a single part Vacuum Pressure Impregnation (VPI) epoxy.

 

Not sold in small quantities, very expensive, long cure time (more than 12 hours) and not sold to

 

consumers because it emits something really poisonous (maybe cyanide??)   as it cures.   

 

As I stated above, and although this stuff is meant for VACUUM impregnation of  armature coils, simply 

 

heating the armature is enough to effect full penetration to the core of the blank.  See Dave's picture above.

 

A vacuum chamber is not going to give better prenetration than that.   


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#22 havlicek

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Posted 28 April 2018 - 06:39 AM

Some years back (*it's probably been a quite a while by now) when I went on my "epoxy-hunt", I spent days on the internet searching for a suitable material, and then spent days more looking for one that came in less-than-50gal-drums quantity.  The only thing that was harder to figure, but pretty close, was where to get a suitable epoxy for powder coating.  We are playing with industrial processes in a "kitchen table" setting, and this is only superficially like the armature winding/rewinding some of us did back in the 1960's.  The interesting thing about all this is that the mass-produced armatures that come from China in the disposable motors today are still very close to what you got in an old Mabuchi back then, except for the  balancing (when done, and how well it's done is questionable for sure) and the com tab connections.  The high-end stuff today has moved into the realm of sci-fi, not in terms of the actual winding (*the great winders' work back then is still as good as it gets, even by today's standards), but in terms of materials and finishing.  The powder, epoxy, laminations, dovetailed coms, shafts and magnet wire have all taken some big leaps forward...both being driven by, AND making possible short stack arms with ridiculous winds and timing capable of performance figures that seem impossible.

*Just* finding the epoxy alone was really difficult because:

1) It needs to withstand temperatures two-to-three times higher than the typical hardware store stuff.
2) It needs to be very low-viscosity to fully penetrate the coils and kevlar ties.
3) (for me and most home-winders) It needs to have a reasonable cure-schedule.  A 12-24 hour cure at elevated temps would be out of the question for most.

4) Once cured, the material needs to be strong in terms of "shear" because of the extreme stress of an armature rotating, and needs to be hard...it shoudn't dry to a soft or sticky-ish condition.

5) It should be clear.  Of course, this is mostly an aesthetic thing because there would be nothing "wrong" with an epoxy that was otherwise good, but solid-colored, like black or gray.  This is pretty much a "slot car thing", but also as a winder I don't want to cover-up the work I tried so hard to figure out.

6) It should be easy to mix and work.

*Of all the epoxies I could find and get data sheets on, Cotronics' "Duralco 4461 and 4460" were on the very short list (4460 has a higher stated working temp of 600F, but a cure time of 4 hours at 250F which is unworkable for me and I would think most others).

*Then I went and looked at the availability of the epoxies, and ONLY the Cotronics epoxies came in a "pint trial size", and even that is a relatively huge amount for what we do, and considering the shelf life.  While the price is high, it's a LOT of a very special material.  Also Cotronics is basically an industrial supplier and they have to actually make up these "trial kits" as a side thing.  The price may seem high, but when you consider all things, thank goodness they sell the stuff at all in such "small" quantities.  If they didn't, a thousand home-winders would have to pool resources to buy and share a drum at a time :)

*There may be other suitable material out there that ticks all the boxes, and I just missed it, but Cotronics has been reliable now after ordering/reordering over the years and they're located in good old Brooklyn, New York.  The Duralco 4461 is really good stuff to boot.  Dave's arm lifting was almost certainly caused by my supply being past it's prime...NOT by a failure of the 4461 per-se.  The arm I built and wound for him is pretty darned radical and would stress any epoxy...but the 4461 fully penetrated the super-tight coils (*and they ARE super tight) as well as any vacuum-bagged epoxy could.  If there's a better epoxy available to home winders, I'd be really surprised.


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