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Are the RJR C-cans too heavy?


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#1 havlicek

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Posted 23 March 2018 - 09:06 AM

     I call "BS", just a little nibbling is all that necessary to wind up with a pretty good weight reduction (*even though I think the can is awfully nice as-is).  To go with the newly more-svelte can, I "figger"...why not a lightweight end bell?".

IMG_2610.JPG IMG_2611.JPG IMG_2612.JPG

     Maybe I saved a couple of micrograms  :D


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John Havlicek




#2 havlicek

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Posted 23 March 2018 - 10:12 AM

I suppose I could have gone with aluminum screws for the hardware and instead of the paper-thin things that come with these NOT (GASP!) modifying PS bottom plates to use instead.  I also thought maybe wearing nitrile gloves so as to avoid the excess weight of the oil from my fingers getting on the setup, but all that would have been silly.  :)

Seriously, this was all "really" about the local series the .560" arm I wound is for.  The only way I can figure to get such a large diameter arm into a C can is to use one without crossmembers.  I kind of jumped the gun though, because I thought I had a .580" magnet hone...and I don't, dagnabbit (*or guldarned it)!  :)


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John Havlicek

#3 Alchemist

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Posted 23 March 2018 - 03:54 PM

Sure looks beautiful John!

 

Ernie


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#4 Bill from NH

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Posted 23 March 2018 - 04:43 PM

When flexi racing ran "built motors" the .560 big arms were used for D-cans, .540 big arms were used for C-cans. 


Bill Fernald
 

How old should a highway be before you tell it, that it has been adopted?


#5 Greg VanPeenen

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Posted 23 March 2018 - 05:29 PM

John is that a Koford end bell. If so you may find it is to light when you watch the bearing end move around when you rev the motor unless the Arm is balanced to all zeros or perfect.



#6 havlicek

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Posted 23 March 2018 - 07:22 PM

John is that a Koford end bell. If so you may find it is to light when you watch the bearing end move around when you rev the motor unless the Arm is balanced to all zeros or perfect.

 

Hi Greg and thanks for the info.  Sure it's a Koford, and I've heard that about this end bell for quite a while now.  I think it'll be fine.

So, I got the magnets set and honed them to .572".  I built and wound another arm just like the one that went to Dave.  Right now, the arm is .562" and JUST clears the magnets, but that will get a slight "true-grind", and the hole will be finish honed to .580".

IMG_2614.JPG IMG_2615.JPG

 


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John Havlicek

#7 havlicek

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Posted 11 April 2018 - 05:26 AM

I'm not sure what's what with this thing.  I got the arm back, .560" with a boatload of CCW timing...like 40+ degrees, way WAY more advance than I ever did on any arm, and it runs really strong, but it needs to be spun by twisting the arm because around half the time it won't self-start.  I have to take it apart to see if anything is wrong, but I think it's just the timing because once it runs, it runs strong.  Weird stuff!


John Havlicek

#8 olescratch

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Posted 11 April 2018 - 03:21 PM

I'm not sure what's what with this thing.  I got the arm back, .560" with a boatload of CCW timing...like 40+ degrees, way WAY more advance than I ever did on any arm, and it runs really strong, but it needs to be spun by twisting the arm because around half the time it won't self-start.  I have to take it apart to see if anything is wrong, but I think it's just the timing because once it runs, it runs strong.  Weird stuff!

You may be in the process of finding out the cause of "other" push-start problems that have been discussed.  Good Luck!


John Stewart

#9 havlicek

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Posted 11 April 2018 - 04:21 PM

You may be in the process of finding out the cause of "other" push-start problems that have been discussed.  Good Luck!

 

 

This has nothing to do with the size (diameter) of the com relative to the width of the brush face John.  I suspect it has to do with the crazy-high timing advance.  The only thing I can see trying is to shunt the brushes, if such high timing means that the motor needs a lot of current for a split second at startup.  If that doesn't work, I'll toss the arm and wind another one with less advance and see what that does.


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John Havlicek

#10 Bill from NH

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Posted 11 April 2018 - 04:22 PM

If the setup checks out okay, as it probably will, you could build a second .560 arm with less timing to see how it runs. If the second arm runs as you expect, you've isolated the problem to the suspected current arm. You could also try the existing arm in another setup to see if it runs any differently.


Bill Fernald
 

How old should a highway be before you tell it, that it has been adopted?


#11 Geary Carrier

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Posted 11 April 2018 - 04:32 PM

Hi John,

 

With that narrow of a crown and that much timing I'm not surprised it starts hard. If the magnets were taller that would help, but of course that ain't gonna happen...

 

The only way to really learn is to actually do it, and you got that covered rather nicely.

 

Besides having things not work is a good thing...

 

 

Thanks,

g


Yes, to be sure, this is it...


#12 Kim Lander

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Posted 11 April 2018 - 04:35 PM

Too much timing....may remidy itself after a few comm trues.....beautiful piece of work .



#13 Kim Lander

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Posted 11 April 2018 - 04:37 PM

Awww heck...just readjust the timing ....lol



#14 Bill from NH

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Posted 11 April 2018 - 05:10 PM

Awww heck...just readjust the timing ....lol

 

Kim, we actually did this to Chinese 16D arms during the late 90's & early 2000's. The amount of timing change depended upon how much slack there was to an arm's comm connections.


Bill Fernald
 

How old should a highway be before you tell it, that it has been adopted?


#15 old & gray

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Posted 11 April 2018 - 05:33 PM

 

 

I suspect it has to do with the crazy-high timing advance.  The only thing I can see trying is to shunt the brushes, if such high timing means that the motor needs a lot of current for a split second at startup.  If that doesn't work, I'll toss the arm and wind another one with less advance and see what that does.

 

For an experiment try cutting the LEADING edge of the brushes. In theory this delays the energizing of the pole and retards the timing. 

 

If it fails someone with a small commutator armature can use the brushes to reduce their push starts. :)


Bob Schlain

#16 Samiam

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Posted 11 April 2018 - 08:22 PM

Try putting  the arm in a set-up with adjustable timing. 


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#17 Bill from NH

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Posted 11 April 2018 - 09:46 PM

Sam, AT setups are only about + & - 5 degrees. John may need more.


Bill Fernald
 

How old should a highway be before you tell it, that it has been adopted?


#18 havlicek

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Posted 12 April 2018 - 06:10 AM

Hi guys,

 

     I've been too busy to really dig in to find the possible cause, but I took apart the motor and the setup is fine.  On my timing compass, the arm reads a little over 40 degrees and a little under 45 degrees.  I know it has nothing to do with the lams and wind, because I built an arm using the same exact combination for Dave and he says it runs really well.  So...I can try:

1) Different brushes (hey...you never know!?)
2) The same wind with under 40 degrees advance (35-40 degrees advance)

     For me, it's far easier to just wind another arm like I said above ( ;) ) than to start messing with timing the setup.  When the motor runs, it doesn't draw all that much current (*although it's possible that it does for a split second at startup and that is too fast for the PS meter to register), and is fast and doesn't get all that warm at all.  If the motor ran like "doodie", then there are all kinds of other things I might have to look into, but since it runs well, I'm even more suspicious of the timing.  I wind hundreds of arms and the only "different" thing here is the radical timing.  The rest of the motor...the magnets, armature stack etc. is just an ordinary DC motor after all.


John Havlicek

#19 Samiam

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Posted 12 April 2018 - 06:19 AM

John,

Did the comm somehow move during the grind and balance operation?  


Sam Levitch
 
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#20 havlicek

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Posted 12 April 2018 - 06:27 AM

Hi Sam,

     No, as per above, I checked the timing and it's over 40, but definitely under 45 degrees.  Using a protractor type setup, it's pretty hard to be more accurate than that.  Nothing (*other than timing) is in question here.  There was also a very nice/even brush track on the com itself.  I also re-metered the arm, and it meters perfectly, so no dead poles or intermittent com connections.  *I'm pretty sure I covered all the usual possibilities :)


John Havlicek

#21 Bill from NH

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Posted 12 April 2018 - 07:15 AM

16D's have been sucessfully running 40+ degrees of advancement for over 15 years. They did have some problems when they 50 degrees. Before you pitch the arm & if you have the time, set it up in a stock 16D setup to see if it runs any differently. Sometimes, the "right combination" of parts just doesn't work with a particular arm. On paper it looks good, but physically it's a different matter. As an aside, the original RJR "fat arms" had low timing, I believe 30 degrees or lower. It's been others that have bumped the timing up. At one time, comm diameter was critical in getting these arms to run well.


Bill Fernald
 

How old should a highway be before you tell it, that it has been adopted?


#22 havlicek

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Posted 12 April 2018 - 08:10 AM

Hi Bill.  Yes, I'm aware of all of that, but again, this exact same arm in the same basic setup is identical to one I did for Dave Parotta, who says the combination worked very well.  I do have some 16D setups before I chuck the arm, but that would change what has already been tested.


John Havlicek

#23 havlicek

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Posted 12 April 2018 - 03:49 PM

TA-DA!  It was the brushes...or actually ONE brush.  I swapped the brushes for another pair and, as much as I "thought" it ran well before, now it REALLY runs well...like scary well.  Current draw is up to around 3.7 amps, but the motor still doesn't seem to get too warm, and all-in-all, it "feels" like a much bigger wire arm than a 50/29!

***This is the second time in maybe 2 years I got bit by bad brushes, but when all else seems OK, it IS something to check.

 

IMG_2691 SMALL.jpg


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#24 boxerdog

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Posted 12 April 2018 - 05:33 PM

I seem to get bit by bad brushes a lot, and I'm not loyal to any brand. Maybe 5% or so? I leave them at the track for "bait". 


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#25 Phil Hackett

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Posted 12 April 2018 - 06:08 PM

I suppose I could have gone with aluminum screws for the hardware and instead of the paper-thin things that come with these NOT (GASP!) modifying PS bottom plates to use instead.  I also thought maybe wearing nitrile gloves so as to avoid the excess weight of the oil from my fingers getting on the setup, but all that would have been silly.  :)

Seriously, this was all "really" about the local series the .560" arm I wound is for.  The only way I can figure to get such a large diameter arm into a C can is to use one without crossmembers.  I kind of jumped the gun though, because I thought I had a .580" magnet hone...and I don't, dagnabbit (*or guldarned it)!  :)

 

This is off-topic but related to the discussion of weight.... I watched a YouTube video regarding the separation of U235 & U238 by centrifuges and the expert told a story where a US Atomic Energy inspector was in Iran inspecting the centrifuges. He picked up the centrifuge tubes with his bare hands and put them back down.... He (the inspector) then said because of the natural oil in his hands getting into the pores of the metal that the tubes were now useless for the extraction of U235. No amount of cleaning could get them back into balance.....

 

Back to the RJR can topic....


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