21 replies to this topic

[havlicek]

Sometimes I ask myself, "Do (sane) people know what goes into bringing back an old motor?" Then I answer myself, "of course they don't!".  

 

Here's a nice Mura, that's all Mura (well, there's a bit of Champion endbell hardware in there if you check out the bussbars... but not at all inappropriate).  

 

The armature was made up from reclaimed Mura .007" lams pressed onto a new shaft and topped off with a reclaimed Mura commutator and then wound with #28 wire. There's more work in just getting the parts off old motors, cleaning them up, and making a motor out of them here than say four "regular" vintage builds. Those .007" lams are pretty fragile and pressing them into a nice stack to be powder-coated is a whole different thing than using nice new .014" lams.  

 

"Unwelding" the comm tabs and then pressing the comm off it's old shaft is no picnic either!  

 

Then there's the winding itself... not a lot of real estate in there compared to modern lams, or even compared to old Mabuchi lams for that matter.  

 

Then again, there IS the "payoff", because you wind up with a classic motor that will run just like it would have when new... maybe better!  

 

-john

[W. J. Dougherty]

Beautiful job...  

[havlicek]

Thanks, WJ.  

 

I could have taken the motor further with more bling on the EB hardware, and may still, but there's already way more work in the darned thing than I'll ever get back... and it still has to go out for dynamic balancing!  Good news is that it seems to have good "natural balance" as is, so it shouldn't need much to bring it into balance.  

 

#28 and #27 winds are always a good bet too, because they're capable of really good speed and power without things melting and people running in all directions screaming and ducking for cover.  

 

-john

[CafeBikeGirl]

Hi John!

 

New member here.

 

Do you ever use the thinner laminations from these motors to construct armatures that are more efficient in newer competition motors or is the practicality not there for it to be worth the effort or gains?

[Tex]

As usual, John.... schweet!

[havlicek]

Thanks, Tex. 
 

Do you ever use the thinner laminations from these motors to construct armatures that are more efficient in newer competition motors or is the practicality not there for it to be worth the effort or gains?

 
Hi Evelyn and welcome to Slotblog.
 
I do very few of these from .007" lams because they're very difficult to get... mine are all salvaged from old Muras, since I have no access to new .007" lams or even know if anyone has even had them stamped, and that is a huge PITA. The Mura lams have a very thick winding leg and crown also, which leaves relatively little room for winding.  
 
There were other thin laminations (*I think it was Champion or someone who had .005" lams), but from what I see... all or almost all modern lams are stamped from .014" steel. Even the really high-end stuff (Eurosports and Open arms) that I've seen are made up from .014" lams, but that's not to say that there aren't rods of .007" lams "out there" that have been held onto.  
 
I have never seen .007" lams in a modern design, but have come across some other old lams that are a little easier to wind than the Muras. The Mura lams do seem to work especially well once you get past the difficulty of winding them (which may be why a lot of the old Mura arms are wound so sloppy), and I don't know if it's because of the thick leg/crown as well as the thin lams or not... probably both.
 
On these old Green Can motors that are still popular "classics", I figure it's worth all the extra effort to use the Mura lams when possible because it's so obvious when you look in there.  Not only are the thicker lams easy to spot, but the new slot car lams "mostly" all have the groove running down the stack.  You can get new lams without the groove, but it's still fairly easy to spot a thick .014" lam as opposed to a .007" lam.
 
Even though the thin lams have performance advantages, they are more finicky to assemble and press, and I've been told they will even deform outwards in today's super high rev motors because of centrifugal force... ESPECIALLY when the stack is ground down to the small diameters (.490" or even .480") used in some motors. With a tight setup, it wouldn't take much for the arm to contact the magnets and... bye bye!
 
-john

[CafeBikeGirl]

Hmmm... I'm not so sure that a .007" lam would deform more than a .014" simply due to the change in thickness when experiencing high centripetal forces. The outward direction of the force is acting along the geometry of the lam, not against the thickness. Not only that but if you half the rotational mass you will also half the centripetal force. My guess is the .007" deflect not because of being thinner but because of manufacturing differences. Sounds like a great reason to do some FEA analysis for fun. :-p

The next time you come accross one where the laminations came in contact with the magnet I would love to do some analysis on some of the pieces. If they are flexing that much I should be able to see something if I do a micrograph provided I can get ahold of the right etchants to look at the grain structure. I work mainly with nickle-based super alloys in the lab so most of the etchants I have really tear up iron-based alloys.

[wbugenis]

In actual experience, the armatures with .007" lams do swell by a thousandth or so after spinning over 100,000 RPM. The .014" laminations swell less.

The guys who insist on usnig them these days - mainly  world champoin racers from the Czech Republic - routinely OD grind them when they get recondtioned and rebalanced.

[havlicek]

Hmmm... I'm not so sure that a .007" lam would deform more than a .014" simply due to the change in thickness when experiencing high centripetal forces. The outward direction of the force is acting along the geometry of the lam, not against the thickness.

 
Seems pretty clear to me that the tips of the segments are being acted upon perpendicular to their outer edge (of course the force isn't being applied to the lams' thickness, but each lam being twice as thick should be better able to resist that force) and that a piece of metal twice as thick, but the same height would deform less under those circumstances.  
 

Not only that but if you half the rotational mass you will also half the centripetal force.

 
Certainly so, and that would be more significant if the lams were all acting completely... or being acted upon completely by that force as individual pieces, and of course that isn't so! The friction between those pieces, not to mention the powder coating acting to bind them in this case changes the physics involved.

Anywho, I haven't seen this happen myself and am just relaying the info I've gotten. I tend to think that .007" lams are just a PITA to handle and assemble and that may be a more significant reason than any why you don't see them used much anymore. Personally, I really dislike winding the Mura .007" lams, they're nothing but a headache!
 
-john

[Dan Miller]

The .007" lamination material available today is soft. Highly magnetic and efficient but soft. The .007" material is now heat treated in a different way than it used to be. In the past, early armatures made from .007" held up quite well, as the material was harder. It's a long story I will not get into here. Please remember that the older .007" or even the .005" thick lamination Champion blanks never saw close to today's RPM. 
 
The armatures made today from .007" do have the problem where the pole face tips will move outward, like Gull wings. Sometimes they can move far enough to hit the magnets. Bill Bugenis is quite correct, pointing out that some very serious Scale racers, do use armatures made from today's .007" material. This is knowing full well that they will have to include regrinding the armatures round again, as part of their normal armature service. Then they true and balance the arms after the regrind to round.
 
At this time, I make either .007" or .014" thick laminations for use in EuroSport Scale armatures. Having wound many arms, based on both lamination thicknesses, I can say that there is no clear cut winner. While the .007" may run better than .014", it will expand during a race, which sort of messes up the balance. The harder .014", while working quite well, does not have a tendency to expand, thus the armature has a better chance to stay in balance during the race. With the .007" material available in North America, there is only one supplier, and a limited alloy choice to be had, in a price range that slot racing can afford. The .014" has much better market coverage and can be had in small, relatively inexpensive amounts, with a good choice of alloys available. It is my thought that the real good .014" material comes from overseas.
 
The winner of this years ISRA 1/24 Scale Championship, Antonin Vojtik, used three armatures to win that event. He qualified and raced two arms that were 20/25.5 winds with one being .007" and one being .014" lamination blanks. For the main, he plugged in a 19/25 made of .014" laminations and ran away and hid from everyone else in the main. Please note that Antonin is a great driver, was really on his game during the Worlds and that he had a super car to drive. In previous major Scale races, held around the World, in the last couple of years, there have been wins using both .014" and .007" laminations. Many of these laminations came from the same die, thus the interior design, of both blanks used, was the same. I cannot honestly call a winner as armatures made from either thickness lamination material can end up winning. Qualifying may be a different story but the main theme is to win. 
 
I like using the .014" material for a few reasons that are practical during the manufacture of armatures. The .014" is also stronger, thus the arms will not deform as readily as .007" arms. The .014" has shown very reasonable performance when up against .007" arms. I do admit though that the finest Scale racers in the World still order many .007" Scale arms. When it comes to Open class, Wing car armatures, forget about using .007" as those arms cannot take the sustained high RPM of today's King tracks.
 
While I am here, talking about laminations, let me say that none of the six armatures dies I use have any groves in the pole faces. Those grooves basically serve as a guide to help center the drill bit when balancing. At that, the grooves do a good job. They do nothing to enhance the performance of the armature. They may even be somewhat detrimental.
 
Dan Miller

[havlicek]

Thanks for the info, Dan.
 
-john

[havlicek]

I have never seen .007" lams in a modern design, but have come across some other old lams that are a little easier to wind than the Muras. 

 
Correction. In reading this, I was reminded that Mura did sell .007" lam arm blanks for a while when I started winding again. It was an odd lam in that the winding leg tapered from thicker at the outside to thinner at the inside by the shaft. Kind of a bother to wind in some cases and I have no idea how well they worked compared to other designs. I guess (?) the design allowed for more room to wind and still left plenty of "meat" at the outside for drill balancing. Where the leg met the shaft radius, it was quite thin and where it met the backside of the crown (outside), it was about as thick as the Mabuchi leg.

 

Since Mura evaporated into thin air some years ago, I've never seen those blanks again... nor have I seen those really fat comms that Mura had ("Diamond Cut Comms") towards the end either.
 
-john

[wbugenis]

Also, you have wound some .007" blanks for me. They were coated blanks so it was hard to tell.

 

Bill

[havlicek]

Also, you have wound some .007" blanks for me. It was the Curry Champion blank (later used by Go Fast with the aluminum comm), 
a direct copy of a Dan Miller (PK armatures) design. They were coated blanks so it was hard to tell.
 
Someone with more info than I will have to fill in how this lamination came about.

 
Who knew!?  
 
-john

[Dan Miller]

John,

I do recall that Monty Ohren, of Best O' The West products, had a taper web blank that he had made. As you described, it was an odd design to hand wind on. Sort of a copy of some R/C blanks I have seen, which seemed to be designed for machine winding. This design idea of a taper web never caught on in slot racing. The blanks seemed to be rather slow and not so efficient as a standard, straight web blank, as well as being a pain to hand wind.
 
I only knew Mura when they were using Kirkwood commutators. I had heard about Mura going off shore, to have a commutator made in their last few years of slot racing production. It was the fat commutator that you mentioned and maybe not as good as the Kirkwoods.
 
To answer Bill, in regard to the Kerry Champion copy of my PK Open blank, Kerry thought he would make arms so he looked at a design that worked. His project was shelved, halfway through, for some time. Tracy Brown of Go Fast Products picked up the Kerry Champion project and ran with it for awhile. I am not sure if that effort still has a life. Tracy is very busy with other projects at this time.

[havlicek]

Hi Dan,
 
Yes, I had heard about Monty's blanks from someone else also, but never saw one. It really was (as you said) a strange thing to wind, although you could get used to it. Working away from the shaft, the design forced the wire tight. Working back towards the shaft, you had to pay attention to keep it tight.  

Those fat Mura comms were seemingly really good quality and, from what I saw (I probably went through two or three dozen or so) were very concentric/round and robust construction-wise. I can't say what effect their larger OD had on things, but no one ever picked up on that, so it must not have been an advantage.
 
-john

[Dennis David]

I'm really struck by the level of discourse on this thread. Great stuff, guys!

[CafeBikeGirl]

I find the term "discourse" being used on a slot car forum slightly amusing. I guess they do crash from time to time, LOL.
 

I can't say what effect their larger OD had on things, but no one ever picked up on that, so it must not have been an advantage.

 
I would imagine the higher surface speed of a larger diameter comm would be harder on brush wear and also be more sensitive to variations in concentricity. On the other hand you would have a wider range of timing without running into overlap issues and it probably handled heat better, probably a moot point since it seems you guys prefer to weld instead of solder. I would think it's probably only worth running a larger comm if you are running into specific problems with your motor set-up and it sounds like most of you have worked those out.

[havlicek]

and it probably handled heat better, probably a moot point since it seems you guys prefer to weld instead of solder.

 
It's really not a matter of "preferring" to weld than solder. Anything hotter than a decent #29 wind... maybe a #28... will often toss (melt and then throw the comm connection) a wire.  
 
-john

[Marty N]

Monty's .560" taper leg blanks, by design or by chance, allowed for one less layer on the coil while winding 60t/28s. Taller, thinner coil with a bit less couple.

At least that was his story when bending my ear.  Which he could do for hours.

[Dan Miller]

John,

 

The fat Mura commutators you worked with were certainly not from the first batch of Mura-made commutators. Those commutators were popcorn, while the second batch was just fine for lower class arms. The large diameter would often not fit into the endbell hardware as it would hit the brush hoods. The math we now use for endbells and hoods is based on a commutator diameter of .210" or very close to that.   

 

You are quite right about welding vs soldering. I could not imagine a modern day armature surviving with soldered commutator connections. The amount of heat generated by the blue plasma ring surrounding the commutators, caused by the brushes pumping considerable DC electricity into them, is quite substantial. Our commutators must heatsink somewhere and that is through the tab end of the commutator, the glass wrap, and the epoxy. A great deal of heat passes into the coils and then is air cooled by the spinning of the arm. Even in lower class Formula 1 armatures 560 degree solder just does not stay put.

 

Also the heating of the commutator, with a soldering iron, is not so good. Properly heat sunk welding (which really should be called resistance brazing ) is the way to go.

[havlicek]

For sure, Dan. The inside of the endbell hardware most often (always?... I forget) had to be radiused out to clear the comm, and it got really messy, really quick if you didn't!  Those comms measure somewhere close to .250" or so.

 

-john