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Old 09-17-2003, 09:29 AM   #16
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well this is what i'm tossing around.

max temp is around 200*F
ambient is usually 70*F
change in temp = 130

CTE for hardened carbon steel is 5.94 uin/in

the distance between bushings is about 1.5 in

the equation for thermal expansion is delta legth = (CTE)(length)(delta temp)

so that yeilds .0011583 in of expansion for a 200*F armature. huh.


and i would expect the can to lengthen some as well to further minimize the possibility of compression. there are some other factors such as the bushings and shims, that will expand oposite the arm adding to the possibility of compression. but so far i would consider them negligent due to their small length displacement. does brass expand 100 times that of steel? well i bet if it did, it would also bind down the arm due to the diameter, both shrinking on the bushing and growing on the arm.

someone please site my errors, because i've heard a ton of reputable people say that thermal expansion is a concern, when, so far, i can't logically believe it.

what substantial piece am i leaving out? infact, i am going to shim up a motor tonight and ramp it up and down in an oven and record the reduction in play with change in temp. i'll post my findings tomorrow.
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Last edited by seaball; 09-17-2003 at 09:34 AM.
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Old 09-17-2003, 10:09 AM   #17
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ah hah!

CTE for abs and nylon range between 35 and about 110 uin/in. that's roughly ten-fold that of the the metal components. it is now conceiveable that the endbell is primarily responsible for the binding of tightly shimmed motors. i would still believe that the endbell would stretch, and not compress, but this definitely makes the anticipation grow for tonight's experiment.
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Old 09-17-2003, 10:59 AM   #18
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Quote:
Originally posted by seaball
but this definitely makes the anticipation grow for tonight's experiment.
Cool, should be interesting to see how much it really does expand.

One other thing, why dosn't everybody just use thin fiber washers instead of metal washers?
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Old 09-17-2003, 11:14 AM   #19
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Default Motors in Heat

seaball;

Simply put, it is the current through the Windings that is actually creating the Heat. The Can just absorbs whatever is there, and surely is quite less than what the Armature is obtaining.

Also because of Heat soaking, overall Motor temperature will incease for several minutes after a race/run and your readings will be higher than actual running temperatures, with air moving over and through the Motor.
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Old 09-17-2003, 11:28 AM   #20
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i use metal washers so that they don't wear over time, and well, they are plentiful. i don't even use the big fiber washer at the top. as long as you have something spacing the com from the bushing you won't short out the com. i try to make sure my outer shims are teflon too. lubricity.

the thing about metal is that it is strong. which means you can get ultra thin shim stock and not ruin them in handling or actual usage. i used to get freaky with my shimming, but most of our fastest guys will use minimal shimming. our guy who ran in the Amain at last year's cleveland indoor champs only used a .010 on each side, leaving about .030 of play.
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Old 09-17-2003, 11:35 AM   #21
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motors in heat.

pops, yeah, i should have thought of that. but by that token, the armature would have to change in temperature by around 1000*F to get .008 growth in length. i don't think the epoxy coating on the arm could get nearly that hot and hold up.

does anybody know what the temperature differential is between the armature shaft and the can ? i've got to believe that the relative proximity between the two objects would keep such a large differential from existing.

damn, my little experiment will be worth very little. i suppose i will have to load a motor and run it while measuring temp. and periodically stop it and record the slop. huh, more difficult, but i'm still curious to verify these claims.

i will report!

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Old 09-17-2003, 12:01 PM   #22
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you guys are making the heat in your brain build up and causing your brain to expand
you guys i have been racing for fifteen years and i build some fast stock and 19t motor your putting to much into this
spin the motor and see where it stops in the magnetic field shim it with about .005
and youll be set the motor doesnt expand as much as you think i am an automotive technician and in and exhaust system where the temperature exceed 1200 deg's
and expansion there is about 1 to 2 inches in length and about 1/2 inch in circumfrance. now we are are talking about mild steel not hardend or treated .
thats a lot of growth but these small motor will achieve temps of about 280'deg
max . so the heat growth is probably very minimal. and its not a constant heat cycle like a full scale car or even a small nitro car where the gas expands in a cylinder bore and is expelled thru and exhust pipe. electric motors dont experiance that type of heat.
so about .005 inc is more than enough.
take a motor do dyno pulls with in at full temp being run in a car with tight shimming and .005 shimming and check to see how much the performance tapers off. try it.!
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Old 09-17-2003, 12:26 PM   #23
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Thumbs up

i never meant to imply that all my testing or hypothesis are going to make a faster motor or find anything new. what i do with my motors is pretty standard, and i doubt my tests will yeild anything to change that.

when someone reputable tells me somthing that doesn't jive with what i've been taught as an engineer, i've got to find what i'm missing. i'm not someone who puts much into what people say without a concrete reason. i've seen a lot of hype propogated by these forums and that leads to bad decisions. this is a great board, and readers want to trust in the content of what they read so as to become faster/better etc.

while rctech is a hub of information, false information can be worse than none at all. this thread is NOT an example of that. i agree with all of the techniques in the preceeding posts. i just want to verify the reason behind them. if an electric motor doesn't expand but .001, than why do some of the fastest dudes use loosely shimmed motors? laziness? dunno. we'll see.

lata.

disclamer: this is not a pissing match.
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Old 09-17-2003, 01:26 PM   #24
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Quote:
Originally posted by speedxl

take a motor do dyno pulls with in at full temp being run in a car with tight shimming and .005 shimming and check to see how much the performance tapers off. try it.!
Actually I HAVE done this myself.

Back to back testing with several different Motors on my Robitronic Dyno. Anything less than .008 (total), Power and Rpm were significantly down. Endplay being measured with Digital Calipers (accuracy .0005).
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Old 09-17-2003, 01:30 PM   #25
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Quote:
Originally posted by seaball
well this is what i'm tossing around.

max temp is around 200*F
ambient is usually 70*F
change in temp = 130

CTE for hardened carbon steel is 5.94 uin/in

the distance between bushings is about 1.5 in

the equation for thermal expansion is delta legth = (CTE)(length)(delta temp)

so that yeilds .0011583 in of expansion for a 200*F armature. huh.


and i would expect the can to lengthen some as well to further minimize the possibility of compression. there are some other factors such as the bushings and shims, that will expand oposite the arm adding to the possibility of compression. but so far i would consider them negligent due to their small length displacement. does brass expand 100 times that of steel? well i bet if it did, it would also bind down the arm due to the diameter, both shrinking on the bushing and growing on the arm.

someone please site my errors, because i've heard a ton of reputable people say that thermal expansion is a concern, when, so far, i can't logically believe it.

what substantial piece am i leaving out? infact, i am going to shim up a motor tonight and ramp it up and down in an oven and record the reduction in play with change in temp. i'll post my findings tomorrow.
LOL, Engineers, LOL! If Switzer had internet right now he would be all over this, LOL. You da man Chris.
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Old 09-17-2003, 01:33 PM   #26
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Default False information

Guys;

I too was shimming my Motors to .005 per the advice of many 'experienced' racers in these Forums.

What made me change my methods was as 'seaball' has stated and my personal Dyno testing results.
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Old 09-17-2003, 01:55 PM   #27
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sea ball your info is informative , but what happens is some of the thread readers this info might be to advanced . i as a master automotive technician working on the modern cars that i repair must have a multitude of skills be it engneering to being a computer hacker aswell as a simple mechanic its just that when someone as myself has been racing for about 12 to 15 yrs you learn alot via the seat of the pants testing i said .005 play i should have been more specific and said
about .008 to .008 total taking into account fore and aft movement .
guys just make sure the arm is in the center of the field and shim it until it moves about .008 to 010 usually an experianced racer can eyeball this.
now i can here all the engineers going oh my god.!
but the fact is having raced closely with some of the fastest factory guys around they just slapped the motors together byy eyeballing it and their motors rip, granted with all respect its is informative to read all this and really know the mechanical theory for it especially for the young guys starting out .
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Old 09-17-2003, 02:15 PM   #28
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When you put current to the motor, the arm will natually try to center itslef in the magnetic field, so the best thing to do is give is plenty of room in whichever direction it wants to go, so that it CAN center itself. If you shim it in one direction, all you are going to do is provide more resistance. I run just the fiber washer on top of the comm, no other shims required, and my motors FLY.
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Old 09-17-2003, 02:49 PM   #29
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hardly, where is switzer anyway? i too think that it is not necessary to always know the details to get the results. and, unfortunately, engineers often cause more problems than solutions. but there are always a few inquisitive folks out there looking to find that stuff out.

i guess what i've seen, and perhaps what pops found, is that many people are shimming to tight tolerances, and the armature may not be sandwiched, but improperly shimmed AWAY from the center. then, of course, widening the window of play let's the arm finally get to the center of the field. i have found that the natural friction of the bushings tends to keep the arm from always aligning itself when checking. just by a few .000ths though. oh, and yes, i do reem the bushings.



till later.
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Old 09-17-2003, 03:19 PM   #30
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I have always found it very difficult to find the natural magnetic center in my motors.
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