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Pablo's FK motor skewed brush orientation experiment


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#26 old & gray

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Posted 10 February 2018 - 10:57 AM

Part of the issue with your experiment is the brushes are not square, so you are not just changing the curvature, but also changing the wraparound.

 

So there can be motors with vertical brushes and horizontal brushes. This will add something else for people to post about.

 

And yes in my limited experience with Group 12 motors I felt there was a difference in performance of my Koford setups when I changed the orientation of the brushes.


Bob Schlain




#27 Fast Freddie

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Posted 10 February 2018 - 11:58 AM

As Mike said the brushes are not square so you will also be changing the timing.  Similar to going from a vertical brush to a horizontal brush.  This also increases brush overlap if there is any.  


Fred Younkin

#28 Dave Crevie

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Posted 10 February 2018 - 02:24 PM

The brush springs are a phosphor bronze spring material. Any experiment involving the springs must also use

the same type of material. You can change width or thickness, but the material must be the same if any results are

expected to be representative.

 

In my experiment I pried the brushes out of the leaf springs and filed the tabs square. Then I carefully added the

tiniest bit of solder in the remaining space in the spring to lock the brushes in the 90 degree orientation.( Solder

won't stick to the brush material ) I then re-assembled the motor and checked the RPMs using a vibra-tach and the

temperature using an infra-red thermometer. ( Both items left from my gas R/C car days ) The motor ran slower and

hotter than it had before the change. The motor I used was brand new, not broken-in in any manner. The tests were

performed at both 6 and 12 volts. I don't have my notes in front of me, but if I find them I will post them.

 

The results indicated to me that the brush face contour has two purposes. First to allow the comm to run cooler. Second,

since these motors are not broken in before their intended use, the brushes would seat in more quickly. Since normal

manufacturing practices make it impossible to assure that a brush contoured to the comm diameter will be aligned

with the arc of the comm in this type of brush arrangement, contouring the brush to exactly conform to the comm

radius does not make sense. You must also keep in mind that these motors were intended to be used intermittantly,

and only in short spurts. Not pushed to their limits for three minutes at a time.    


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#29 Pablo

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Posted 10 February 2018 - 04:33 PM

Thanks Dave. Just a reminder this isn't intended to be a real scientific experiment.

Just something I've wanted to try. There must be something to it, or else JK Products® wouldn't have publicly announced intentions for 2018 to change the orientation.

 

We all know I am just a guy with a screwdriver and some soldering irons. Let's not get too serious here.

I am also aware I cannot duplicate the brush holder/leg setup.

But I think at least I can make it work just enough for me to listen to it and feel it run.

 

Now, where did I stow that Hakko 454? :laugh2:


Paul Wolcott

#30 Fast Freddie

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Posted 10 February 2018 - 06:11 PM

Dave your correct in the sense that these motors were designed for another purpose and so the brushes are positioned to provide longer life to that end.  The slot car racing community has almost always ran contoured/seated brushes for the best performance.  Now that we have motors with brushes that are not seated this in itself lends to the belief that the motors are not running at peak performance.  I have been messing around with a H7 that has the 2 speed problem and yet it is balanced.  The brushes are completely broken in, the comm. is nice and clean, the arm doesn't seem to tend to either end so why the 2 speed problem?  Today I tried something that just about everyone will probably say "that's a no no".  Every time I read about how to oil this motor when it comes to the EB bushing just waiving the oiler over the bushing should be plenty of oil.  Well today I oiled the hell out of that sucker and the can bushing too with the lightest Mobile 1 synthetic oil I have.  The motor ran smooth as silk, no 2 speed, all the way to 13 volts and it sounds very good.  Tomorrow I'm going to try this on my other motors that have a 2 speed problem and I'll let you know what happens.


Fred Younkin

#31 zipper

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Posted 10 February 2018 - 06:29 PM

Might be bad balance, abundant oiling prevents arm shaking in slightly loose bearing(s).


Pekka Sippola

#32 Pablo

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Posted 14 February 2018 - 06:58 PM

Experiment over. I was unable to successfully make the brushes do what I wanted.

At least I tried. Even if I had been able to orient and place the re-oriented brushes correctly, as Swiss pointed out,

the brushes aren't square so the overlap would have been different.

 

Foghorn goes back in the junk bin, Leghorn sits in a tire bottle labeled "H7 - dud", and life goes on.

No strain, no pain  :sun_bespectacled: 


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Paul Wolcott





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