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Questions regarding timing


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#1 havlicek

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Posted 05 January 2018 - 08:51 AM

     I get these on a semi-regular basis, and here's an answer I gave most recently about the stated timing advance of an armature being "possibly" (*if the person is reading the timing correctly) being off by 7 degrees.:

"   On a 3-pole armature such as yours, timing is pretty easy to figure, and for me, the most accurate way to read the timing is with a "protractor" type setup.  With the gap between two poles sitting on a flat surface, a single pole should be facing upwards.  Then, the slits between two commutator segments should be exactly in the center of the armature poles for a "neutral timing" armature.  As the slits move towards the poles' edges, the timing is advanced, and you can read the degrees of advance by having an indicator in the com slits reading against a protractor.

*In reality, many people only "come close" to the stated timing advance and sort of guess at what it is.  Without strictly setting-up jigs to make sure the timing is both exactly what is stated, and remains consistent, there will usually be some variation.  To me, being off by 7 degrees seems like a lot though.  Anyway, timing isn't really "arguable", being a mathematical/physical relationship between the com segments and their associated poles, and your gauge should be telling you what it actually is, rather than what a manufacturer says it is."

With a protractor, the accuracy of somewhat dependent on how perfectly the indicator fits the com slots, as well as how long it is and how large the protractor is, but these are generally very accurate.  There are relatively expensive electronic devices that I *think* might be even more accurate, but the reality is that a "couple of degrees here and there" aren't all that consequential in the scheme of things.  Personally, I'm not all that anal about timing-statements, although when a person is REALLY intent on having an armature built and wound with a really specific amount of advance...I give it my best shot.  :)

 


John Havlicek




#2 gotboostedvr6

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Posted 05 January 2018 - 09:04 AM

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Armature timing and Aftermarket timing fixtures.



Armature Timing - For simplicity's sake, think of the commutator as the "switching system" for turning the poles of the armature on and off in their function as electromagnets. "Armature timing" is the term used to describe the relationship, in degrees, of the segments of the commutator to the stacks or poles of the arm. As you can see in Figure 1, below, armature timing is expressed in degrees of advance from a base of zero at the nominal centerline of each stack leg. Looking at the com end of an armature, one with 0° of timing would have the leading edge of its com segment - or the trailing edge of its com slot(s) - lined up with the center of each stack leg. A common misconception is that the edge of the armature stack is used to determine armature timing. This is wrong, the stack edge has no bearing on armature timing at all. True timing is figured from the center of the stack leg (which is not visible in a finished armature).

figure1.jpg


The differences between one level of timing and another may appear slight, but slight is all it takes to make a major timing change at the com. Consider it this way: given a com diameter of .202", one degree of timing at the comm is approximately .00178" of its circumference (diameter * pi / 360). Put another way, a .5 mm pencil line is more than 11 "com degrees" wide or a common piece of computer paper .005 thick is 2.8 "com degrees" wide at the same diameter. The slots used in ProSlot comms are .014" wide, in other words the slot itself is 7.8 "com degrees" wide.
They are cut offset from the centerline of the comm. This insures that the leading edge of the comm segment is always on the shaft centerline no matter how wide the actual slot may be.


figure2.jpg

During manufacture we use a specially designed fixture that indexes the leading edge of the comm segment with the center of the armature blank leg. It is calibrated in 1 degree increments through 360 degrees of rotation. The comm is locked in the fixture head and the blank is placed in the indexer and rotated to the desired timing and the 2 components are pressed together in prefect alignment. The blank is then sent to the CNC machine for winding.



To my knowledge the aftermarket industry has yet to produce a fixture that takes into account the offset commutator slot and the commutator leading edge to blank leg center relationship. This accounts for the wildly inaccurate readings people are getting using these fixtures. Aftermarket
fixtures reading incorrectly from the comm slot can be off as much as 6 to 10 degrees because of this.


figure3.jpg



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#3 gotboostedvr6

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Posted 05 January 2018 - 09:06 AM

Personally when I check timing on armatures I use the center of the comm slot. I do this because it's easier for me to see and because its faster and repeatable with minimal error.

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#4 gotboostedvr6

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Posted 05 January 2018 - 09:10 AM

Another thing to consider is the width of the comm slot. ProSlot comm slots are about .015" where as Model Electromotive and PK are .010", Koford ~.012"

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#5 gotboostedvr6

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Posted 05 January 2018 - 09:18 AM

Last thing:

When your trying to squeeze every last Hp from your race motor timing is very relevant. Other things that arm timing effects and you must consider are the magnets tip distance, brush overlap and its effect due to comm diameter, and (heat soak).

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#6 Bill from NH

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Posted 05 January 2018 - 09:39 AM

The only situation timing was an issue in my racing was during the late 90's & early 2000's when running Chinese 16D arms. To a lesser degree, it sometimes became important with the American wound 16D arms. As John said, the timing on both was apt to be all over the side of the barn.


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#7 havlicek

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Posted 05 January 2018 - 11:55 AM

...another potential factor in all this is how accurately the coms have been formed and slit...how exactly the tabs and slits are all 120 degrees apart.  It could be possible for the advance of each com segment as it relates to the associated pole to be slightly different.  I doubt very much that this could be an issue for ProSlot, or Bill Bugenis and PK, but it *might* creep in there for some of the foreign coms (?).  In any case, I have no way of accurately measuring/judging something like this.


John Havlicek

#8 gotboostedvr6

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Posted 05 January 2018 - 12:02 PM

I have many many proslot arms. *A few have issues, the vast majority are good to go.

Considering they only get about $18 per machine wound arm from the distributors, I'd say they go above and beyond.

* none of my proslot arms were produced by the current owner.

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#9 zipper

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Posted 05 January 2018 - 12:10 PM

Mostly the spread is inside 3 degrees, may sometimes be upto 5 degrees and very seldom is 0 to 1. Speaking of Gr 7, Gr 27 and Gr 12 Koford, PK and PS arms.


Pekka Sippola

#10 havlicek

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Posted 08 January 2018 - 07:08 AM

 

 

Considering they only get about $18 per machine wound arm from the distributors, I'd say they go above and beyond.

 

 

The benefits of standardizing production methods as much as possible, and then doing like-procedures in batches.  Aiming for consistency is (to me) just as important as anything else, maybe more so.


John Havlicek





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