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Checking stack length


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#1 havlicek

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Posted 25 November 2019 - 06:09 AM

I had to build and wind an S16D arm yesterday and I came upon a situation that happens fairly often for me.  When pressing the stack and trying for the minimum, I had a choice of being slightly under...or adding that one more lamination and being almost a full lamination over.  This brought up two questions:

1) Does the minimum stack length spec take into account the powder coat?  If there were some sort of a challenge and an arm were measured, some of the powder coat would have to be chipped off the top and bottom of the stack to get a measurement if the powder coat doesn't count.  If the powder coat DOES count (*and it should, because the wire is wrapped over the powder coat which determines the total wire length), what thickness do people assume the coat to be?  These things can vary.

2) Is stack length like hand grenades and horseshoes...like..."close enough is close enough"?  I don't know how anal people get about these things, and/or how often something so difficult to check as stack length is challenged.

Personally speaking, when the choice of one lam either way comes up, I always go over to be safe, but I sometimes wonder if that's even necessary in reality if a "stack length objection" almost never happens.


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#2 Gene/ZR1

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Posted 25 November 2019 - 07:45 AM

As far as desired stack lengths, at one time if I remember correctly didn't they leave out one lam in the middle of a completed stack set ?

That just rung the bell when you commented getting the stack length correct.

What was the reasoning leaving out one lam ? 

g


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#3 havlicek

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Posted 25 November 2019 - 07:52 AM

Hi Gene,

I think you're referring to those segmented stacks where they would put one of more stack insulators in the stack or even just spacers. I don't know what the thinking was there, but the stack length would (presumably) not be affected. I have made a few of those over the years, but only when asked.
John Havlicek

#4 Jesse Gonzales

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Posted 25 November 2019 - 09:01 AM

Amature Stack Length
 

Any armature that has been purposely altered or tampered with to make the stack appear longer in an attempt to circumvent the stack length rules as listed shall be declared illegal at the tech inspector's discretion. Stack length minimums shall be required on all three poles of the armature (using calipers with the faces across each end of the pole) and only the actual lamination material shall be used to determine this figure. This is meant to specifically exclude, for example, such practices as the insertion of spacer-type materials between the laminations, abnormally thick applications of coatings, or any other method of artificial compliance with the rule. Any armature presented for tech inspection that is found to be illegal for competition (such as short stack) will be impounded until the completion of the racing class. Litz and/or flat wire may not be used in any class with armature wire specifications.



#5 Cheater

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Posted 25 November 2019 - 09:10 AM

I believe the above is from the USRA rulebook.
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#6 Bill from NH

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Posted 25 November 2019 - 09:24 AM

Any 16D or S16D racing I've ever done, no one sat down with a caliper to measure stack length for all arms to be legal. Each motor was given a visual check through the cooling holes. It was always easy to tell if a motor had a 16D or a S16D arm. Only at series races have I seen podium car motors opened up & torn down for a closer inspection of the arm & magnets. Not knowing how your arms are to be used, your "erring on the safe side" is probably a good decision. If they were just going to be used in weekly programs or occasional  casual running, I'd say one less lam wouldn't be an issue. When I have measured stack length, I've included the thickness the stack coating, whatever it may be. I never heard there was a standard for stack coating thicknesses.


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#7 Jairus

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Posted 25 November 2019 - 11:28 AM

Guys, there is no way this question was for making a "cheater" arm. 
John is too principled to stoop to such tricks.  He always marks his arms with an "H" and labels the can with a decal.
The question seems innocent enough so please stop with the rule quoting.
Thank you.


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#8 Gene/ZR1

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Posted 25 November 2019 - 12:34 PM

Hi Gene,

I think you're referring to those segmented stacks where they would put one of more stack insulators in the stack or even just spacers. I don't know what the thinking was there, but the stack length would (presumably) not be affected. I have made a few of those over the years, but only when asked.

 

John

Here's a couple of photos of the arm I mentioned.

No insulator between lams, just a gap.

 

You can see daylight thru the gap, I passed a piece of tape thru the gap opening.

Maybe these are just wanna be arms, but it's different.

 

AG1.jpg

 

AG2.jpg

 

AG3.jpg


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#9 Danny Zona

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Posted 25 November 2019 - 01:31 PM

[quote name="Bill from NH" post="766339" timestamp="1574691882"]

Not knowing how your arms are to be used, your "erring on the safe side" is probably a good decision. If they were just going to be used in weekly programs or occasional  casual running, I'd say one less lam wouldn't be an issue.

It's possible one less lam wouldn't be an issue in weekly racing but it can depend on the what racer is using an arm like that.

Some probably could use one and some probably couldn't in my experiences. 😉
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#10 olescratch

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Posted 25 November 2019 - 01:47 PM

Guys, there is no way this question was for making a "cheater" arm. 
John is too principled to stoop to such tricks.  He always marks his arms with an "H" and labels the can with a decal.
The question seems innocent enough so please stop with the rule quoting.
Thank you.

  Correction:  Mr. H doesn't always mark his arms with an H, nor does he always apply a sticker to the cans of his creations!  I have examples of each!


John Stewart

#11 Jairus

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Posted 25 November 2019 - 02:12 PM

My statement stands.


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#12 Bill from NH

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Posted 25 November 2019 - 04:33 PM

 

John

Here's a couple of photos of the arm I mentioned.

No insulator between lams, just a gap.

 

You can see daylight thru the gap, I passed a piece of tape thru the gap opening.

Maybe these are just wanna be arms, but it's different.

 

 

 

I think these split-segment arms were Contenders & Super Wasps wound by Proslot for awhile during the 80's or early 90's. I don't think they were ever too successful. IIRC, I read an article about them in an issue of Slot Car Bulletin. I'll look for it after the holiday.


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#13 Jason Holmes

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Posted 25 November 2019 - 09:25 PM

Gene 

 

The PS Intruders were never USRA Legal and John if they are for Sanctioned race the Jess was right and Bill in 2001 at the USRA Scale Nat's we DQ 3 racers for having short arm's and the Next year Paul C. from Parma sent me all the Team arm's to check to make sure they were legal for 2002 But back then we did a motor tear down after every A main or Final Main

 

jason

 

And I'm sure John has no intent of making Cheater Arm's 


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#14 Jesse Gonzales

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Posted 26 November 2019 - 03:17 AM

back in the day stack lengths were most likely tied to lamination stacks consisting of laminations in the .005 to .007 thickness range. As the costs to keep using thinner and potentially more expensive steels thicker laminations came into play making exact .440 length or .350 length stacks difficult so going over is best if you are going to make arms for USRA races, no sense in having a customer DQ'd over a half a lamination thickness. Some of the mabuchi laminations i've stripped down for experimental arms have been .020 thick steel, probaly not good steel like you might get from some exotic suppliers that still roll .005 or .007 steel.

 

and yes, i did clip in the usra rule, it's easy and accurate. John H. is a journeyman master craftsman and there is only doing it right in his book, I agree with that. many years ago I was approached by some factory racers to wind them "cheater" arms using factory tagging, I refused and I know a guy like John would say no to such a request too.

 

Jess Gonzales


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#15 philk

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Posted 26 November 2019 - 10:18 AM

I think these split-segment arms were Contenders & Super Wasps wound by Proslot for awhile during the 80's or early 90's. I don't think they were ever too successful. IIRC, I read an article about them in an issue of Slot Car Bulletin. I'll look for it after the holiday.

. These were also X12 and grp27 arms also. If I remember right they were called Interrupters not Intruders.
Phil Kreuter





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