119 replies to this topic

[havlicek]

 

 

do you believe the way you encapsulated the windings with epoxy is superior to johns encapsulating,yours is like armatures in the day and is heavier,would that be stronger in keeping windings from migrating or are both techniques equal.

 

 

 

This is the first time I've tried this arm and wire combo and the epoxy was applied a bit too heavy. 

 

 

I wouldn't presume to speak for Geary, since he knows what he's doing...but personally speaking, I'd have gone for a heavier coat of epoxy with such a wind myself, because tall "narrow" coils can be a little less stable.  To me, it's especially good that there's a good amount up by the com end since that's where you really want the stuff.  Looks pretty much right to me!

[Geary Carrier]

 

 

 

I wouldn't presume to speak for Geary, since he knows what he's doing...but personally speaking, I'd have gone for a heavier coat of epoxy with such a wind myself, because tall "narrow" coils can be a little less stable.  To me, it's especially good that there's a good amount up by the com end since that's where you really want the stuff.  Looks pretty much right to me!

 

You're right John, the epoxy for this aspect ratio coil should be reasonably heavy.

 

If I applied this much epoxy without turning it during curing it would have left a large blob at the bottom of the coils but because it was rotating I'm a happy camper...

 

When rotating the arm I always cure at a lower temp first so the epoxy can self level and then crank her up to the final cure temp after initial cross linking has taken place and the epoxy is done moving.

 

Thanks for the look see...

[brucefl]

How do you silver braze a commutator,are you using silver brazing rods that are used with a brazing torch.

Or is it the so call silver solder that's used with an iron?

[havlicek]

How do you silver braze a commutator,are you using silver brazing rods that are used with a brazing torch.

Or is it the so call silver solder that's used with an iron?

 

Hi Bruce,

     This is done with an electrically heated (resistance) piece of brazing ("gouging") rod or other material touching the com tab.  I've shown this many times here before, so you'll have to look back to see the process described in more detail.  ***This is NOT silver-bearing solder used with an iron.  This is *brazing (high temperature soldering) done with a filler metal that melts/flows at around 1100F, give or take.  

[brucefl]

why is that even needed since no component on the fastest G7 armature can handle above 7 or 800f(what koford touts,that i doubt,unless its the new ceramic epoxies) maybe even less since the best epoxy 3m makes for this purpose only handles I believe 450f maybe 650f,so the silver solder Jim Greenaway used that he could change commutaors with was as much as you need.

[havlicek]

Maybe because Greenaway never built eurosports or open wing car motors...but even more probably just because he never *could* (assuming it's true he only soldered his coms). This is like asking why are modern dovetailed coms needed when people wound and ran #24 singles using Kirkwoods.  As has always been the case Bruce, slot car motors have followed a development based on failures and doing whatever can be done to take care of the weakest link...until the next weakest link appears.  Trust me, it's "needed", but not for all arms.  However, if you build and wind arms, you don't necessarily use different methods for arms based on how "important" they are.  If you have a technique that's important to use for some arms, you can then use it for less critical arms with confidence.  BTW, brazing is as fast/easy as soldering, and even with the higher temperatures, may stress a commutator less than soldering because you can get on and off the com much faster.  With soldering, people may tend to stay on the tab with the iron long enough to stress the com phenolic.

***Anyway this (*and welding) are standard today, even for the inexpensive Chinese motors...none of which are soldered, for very good reasons.  Better connections, faster assembly etc etc.

[Dan Miller]

Some of the materials used for the old Greenaway armatures, from back in the past, are not up to the needs of a modern day Gp 7 armatures. Add Scale Eurosport armatures to that list along with a few other group classifications. Any solder that can be melted with an iron is useless today for any form of advanced racing. There is a large gap up from solders that melt about 550*F to silver braze that melts at 1145*F. There is nothing in between that is practical. I would like to see silver braze that melts about 800*F but no luck there.

 

Greenaway arms ran back in the days of 500 to 600 lap totals in a main event on a King track, when the cars lapped at around 3 to 4 seconds. Race laps today for Gp 7 cars are often under 1.7 seconds and 1400 laps in a 40 minute main is expected for the win. Try that with Greenaway armatures, along with all the other armatures from the Golden age of Slot racing. They are slugs compared to todays' armatures. Soldered commutator connections are not the way to go. Brazed are. Forget replacing commutators. That is so impractical with todays' armatures.

 

Vintage armature reconstruction is to be admired. I am all for it. But that is just what it is. Do not make the mistake of trying to incorporate old methods and some of the early materials into race armatures of today. You will just end up with a piece of popcorn.

 

.

[brucefl]

But the weakest link is the epoxy and wire coating which is still no more than 240c which is 464f ,unless you get the ceramic coated wire which goes to 1200c,no one is using ceramic wire,and talking to a 3m engineer there is no organic epoxy capable of exceeding this natural limit of this adhesive,so how can you justify not using solders with the same temperature rating of the other components,it doesn't make sense.
It's overkill and probably more damaging exposing the commutation to such high temperatures,at least that's logical,but maybe you guys are working magic and doing supernatural things.

[brucefl]

Sorry 1200F

[brucefl]

OK can anybody tell me actual max Temps that G7 motors get to,maybe they exceed by a % for the let's 40 minutes heats,and this 40 minutes works with the materials as far as amount of time that they can withstand exceeding limits,obviously there's a limit to this too,maybe multiple arms are needed in a G7 race,maybe 1 for each heat.what are your thoughts,it just makes sense that exceeding the weakest links limit with other components wouldn't increase the life of the arm.

[havlicek]

 

 

But the weakest link is the epoxy and wire coating which is still no more than 240c which is 464f 

 

 

Except the operating temperature of an armature is not uniform.  The commutator gets hotter than the armature coils.  While the entire armature is in effect a "spinning radiator", the coils and poles are naturally MUCH better at radiating heat, especially in an open or "strap" type motor, so the com is also less able to get rid of the heat it's experiencing...which is higher.

 

 

 

unless you get the ceramic coated wire which goes to 1200c

Ceramic wire isn't needed because of the above; the com where the heat is.   Ceramic insulated wire also can NOT be used because it won't make the bends around the top and bottom of the winding legs of an arm (*remember?...I checked the specs, and it's not even close) without it's insulation cracking and failing.

 

 

 

It's overkill and probably more damaging exposing the commutation to such high temperatures,at least that's logical

It's true that 1100F+ silver braze is more than is "needed", but you missed what Dan said.  If there were something in the 800F or so range that could be substituted, that would probably be fine...but there isn't, or at least I couldn't find it, and apparently others couldn't either.  The bottom line is that people use a material that is more than sufficient...***and apply it using techniques that take into account trying to avoid damaging the com phenolic.

***Another point I made (or tried to make, and that you probably missed ) is that brazing com tabs with 1100F+ silver brazing metal may actually stress the com LESS than silver soldering with an iron.  The whole process goes by REALLY fast, faster by far than soldering with an iron. Ironically, soldering may actually stress a com MORE than brazing when done right because you need to stay on a com tab longer with an iron.  That means much more of the com is getting up to temp with soldering than just the tab.

Bruce, trust me when I tell you, all of this has been learned and adopted "the hard way".  Slot racers, especially at the "bleeding edge" are an unforgiving crowd.  When an armature fails, they don't just shrug and say "oh well, no biggie...at least the armature guy did his best".  These motors are doing things that can seem physically impossible...even to engineers, physicists and chemists, and some of those things are operating at ridiculous temperatures and spinning at ludicrous-sounding RPMs.  So again, when you get a technique that works well at the upper limit, it gets used for all sorts of reasons across the board.

Of course, if you want to have a bunch of motors built with armatures using soldered com connections and then go pay racers to use them (*which won't be easy, because what racer would want to lose standing because of the potential of failed arms?), you could certainly do that...but you'd be travelling down a road that's already well-worn only to come to the same conclusions others have. 
 

[havlicek]

PS...your last post is again besides the point.  Armature makers in slots aren't dealing with theory or even specs, they're coming from seeing failures...taking apart the motors...and then making improvements/changes to address THAT issue, until the next one pops up.

***BTW, I believe that actual com construction is the current "wall", and not com connections using silver brazing, with some coms surviving better on *average*.  So, you're focused on something that may be so like..."yesterday". 

[zipper]

Stay Brite Silver (4%) solder melts on about 430°F and when used on pinions, Group 7, tends to give up sometimes so it's the temperature on the armature axle and sometimes more. About on the same temperature the windings begin to give up, too (yeah, experienced it some times...) So the pinions have been pinned or better soldered with hi-temp solder, good for around 600 °F. I suppose comm surface temperature when it turns to red is around 700°F.

[Don Weaver]

Bruce,

 

What's the point of all your 2nd guessing about exotic materials used by the experts?  You can't even 60/40 solder lead wires to a motor.....

 

Don

[havlicek]

Stay Brite Silver (4%) solder melts on about 430°F and when used on pinions, Group 7, tends to give up sometimes so it's the temperature on the armature axle and sometimes more. About on the same temperature the windings begin to give up, too (yeah, experienced it some times...) So the pinions have been pinned or better soldered with hi-temp solder, good for around 600 °F. I suppose comm surface temperature when it turns to red is around 700°F.

 

Pekka, I know you are an experienced racer, so take what I say with a grain of salt.  When the "windings fail" on an armature, it's a leap to think that it was the windings' insulation that caused it.  It could just as easily have been the powder coat, causing a short against the lamination steel (*which DOES happen), either because the powder coat was done poorly...or possibly because the powder itself isn't up to snuff.  Some powders don't get hard enough to resist the kind of tension applied to magnet wire (*especially larger gauges) when winding an armature.  The arm may seem and run fine at first when this happens.  

Likewise, when a solder joint fails (*as in your example with pinions), that may or may not be be cause the arm shaft got hot enough to melt the solder.  It could just as easily be because of poor prep or technique.  It can also be because the solder alloy itself doesn't make for a joint with enough shear-resistance (*strength)

I only say this because it can take some pretty detailed analysis of more than a single failure, the more failures the "better" to reach any particular conclusion.  Of course, if a change is made that all of a sudden results in no failures, then I guess we can assume...with more confidence, what the cause of the failures really was.

[MSwiss]

Bruce,
 
What's the point of all your 2nd guessing about exotic materials used by the experts?  You can't even 60/40 solder lead wires to a motor.....
 
Don

Don,
Some guys like to play Fantasy Football.

Some guys like to play Fantasy Baseball.

Bruce likes to play Fantasy Armature Making.

[zipper]

Likewise, when a solder joint fails (*as in your example with pinions), that may or may not be be cause the arm shaft got hot enough to melt the solder.  It could just as easily be because of poor prep or technique.  It can also be because the solder alloy itself doesn't make for a joint with enough shear-resistance (*strength)

I only say this because it can take some pretty detailed analysis of more than a single failure, the more failures the "better" to reach any particular conclusion.  Of course, if a change is made that all of a sudden results in no failures, then I guess we can assume...with more confidence, what the cause of the failures really was.

 It's a wonder that the hot class motors do run at all a longer heat. On our King the amps for eight Group 7 cars hover at 200 - 280 Amps  - it makes constant 420 - upto 500W into a tiny 20 gram motor. I believe the weakest point is the epoxy letting the windings swell creating an imbalance. Then the amperage rockets and either burns the insulation or throws a wire. The comms break pretty seldom. Group 27 arms are more prone to swelling with their longer stack and thinner wire. Heavy glue use is the decisive culprit, luckily we are more and more turning to spray glue. 

[MSwiss]

Group 27 arms are more prone to swelling with their longer stack and thinner wire.

I'm not sure if you are implying it's because of the physical dimensions of a G27 arm, but the bigger factor is the extra heat generated around the stack from a coil with 4-5 times the resistance.

[Eddie Fleming]

I'm  not sure if you are implying it's because of the physical dimensions of a G27 arm, but the bigger factor is the extra heat generated around the stack from a coil with 4-5 times the resistance.

Mike 

  Would the extra heat not be generated by the Physical dimensions of the arm. "Smaller wire and longer stack (making the wire longer)"?

[MSwiss]

That's why I said "I'm not sure" and asked.

 

Pekka stated smaller and longer, nothing about the resulting higher resistance.

[zipper]

The higher resistance via the thinner #27 wire means that just  about half of the amperage compared to Group 7 motor goes thru. So "just" about 300 Watts to turn into movement and heat. Comparing the stack colour (Koford red) turning darker and winding swelling it seems that Group 27 arms begin to swell at a little lower temperature.

[MSwiss]

My point was 27's heat up at the stack , because of the higher resistance, but the comm stays fairly cool.
 
IOW, you can have a G27 arm and a G7 arm.
 
If the dykem is both the same shade of brown, the comm on the G7 will show much, much more heat.
 
And while the red dykem is a good thermometer, the application of it has a bearing how it changes/appears (thick vs. thin)

[Dan Miller]

Bruce,

 

John said something interesting you should pay attention to. The bulk of an armature is indeed a spinning radiator that cools the commutator.

 

Mike shares his years of race winning and record setting experience and you blow it off. Mike worked for Koford for years. He has built and raced countless motors at the highest level. Mike knows his sh*t.

 

You are just banging away at your keyboard, making comments about how much you know, with no practical experience whatsoever. In other words, you're clueless about high performance slot racing equipment. 

 

The blue plasma ring around a spinning commutator is extremely hot. The blue color is caused by the air being turned into an electrical conductor, at an elevated temperature, measured in thousands of degrees Kelvin. Google that and learn something.

 

In advanced racing, I consider the weakest link in an armature, to be the alloy of copper the commutator is made from. With all the work and testing I put into making my own commutators recently I can state that as a fact. Sure, there are other factors that can effect an armature temperature wise and the choice of materials and their temperature ratings become important but not so much as the copper alloy the shell is made from.

 

How about you make some armatures yourself and step forward onto the World stage of high level slot racing .Go up against armatures from Koford, Camen, Valiko, S & K and others just to see what will happen. We will blow by you so fast you will look like a hotdog wrapper at a NASCAR race.

 

.

[havlicek]

You know, there's a good thing going on here, despite what seems like a "pointless" set of questions.  Some very good information is being tossed-around that almost never sees the light of day in most threads here.  For the majority that are happy not knowing what's going on inside their motors, it's easy-enough to just skip to another subject.  For the rest (*all three of you ), pay attention!

[Dave Crevie]

i agree with you, John. There have been some changes since I rewound motors in the mid-sixties, and I am axious to try some of those

now that I have time. Just as I learned the tool and die trade from the experienced guys. Over the years I have seen many "college

boys" who were thrown into the real world and couldn't make the grade.