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Re: Trimming Pro Slot FK brushes


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#1 SlowBeas

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Posted 02 April 2015 - 02:42 PM

The illustration indicates the width of the trimming that should be performed, but not the length. Obviously, too much and the brush will wobble in the hood and fail to make proper contact.

 

Can someone with experience with these motors suggest a recommended length to cut away?


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#2 Cheater

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Posted 02 April 2015 - 02:51 PM

Jim,

 

This is sort of a personal preference, but I'd suggest a quarter of the overall brush length or perhaps even a little less.


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#3 Ramcatlarry

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Posted 02 April 2015 - 03:22 PM

AND do both edges have to be removed if only one is the problem? Removing one edge (leading or trailing) COULD constitute a timing advance alteration.


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#4 Noose

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Posted 02 April 2015 - 03:36 PM

If you mean is it OK to only remove material from one side in order to line the brush up better to the comm, then yes, it is.
 
Remember this is for Can-Am Plus class only. The only class in IRRA® where this motor is allowed. Has nothing to do with any other organization's rules.  Check your local authorities for any other ruling.


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#5 MSwiss

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Posted 02 April 2015 - 03:55 PM

AND do both edges have to be removed if only one is the problem? Removing one edge (leading or trailing) COULD constitute a timing advance alteration.

 
Larry,
 
What you're talking about is not advancing the timing.

To truly advance the timing, you have to rotate the hoods in reference to the magnets, or vice versa.

When the Hawk 6 came out, I tried every variation, and trimming just one side didn't improve motor performance.

Mike Swiss
 
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#6 Fast Freddie

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Posted 02 April 2015 - 08:50 PM

If you remove material from both sides you are retarding the timing and reducing the overlap. That's why they run so cool less timing and less overlap.

If you remove material from one side and install it as the trailing edge you keep the timing and reduce the overlap. The motor will not run as cool because you kept all the timing but you will eliminate the push start. In this case the motor will run about 50% cooler.

I've done this on PS Contenders with 45 degrees of timing that had push start problems and it eliminated the problem. I only remove enough material to stop the push start, just make them equal.
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#7 idare2bdul

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Posted 03 April 2015 - 12:05 AM

Timing the brushes worked with the bigger R/C motor brushes but I was never able to get a performance increase when I experimented with slot motors. I was using it on the drag strip where it is easier to verify a performance increase.
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#8 tonyp

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Posted 03 April 2015 - 07:08 AM

Me, too.

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#9 Eddie Fleming

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Posted 03 April 2015 - 04:03 PM

I thought the cut was more to stop the push start problem than it was for a performance improvement.


Eddie Fleming

#10 MSwiss

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Posted 03 April 2015 - 04:07 PM

It is.

Guys brought up cutting one side only and we were just pointing out it's a bad idea.

Mike Swiss
 
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#11 John C Martin

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Posted 03 April 2015 - 04:59 PM

My answer to the original guestion is to simply file down the brush (Big Foots) to the bottom of the slot on the spring end... then I cut a new slot with a X-Acto saw blade.

#12 Fast Freddie

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Posted 04 April 2015 - 11:31 AM

Sorry, Jim, I forgot to say I usually cut the first third of the brush. This keeps most of the uncut portion of the brush inside the hood.

 

I don't cut both sides of the brush because I believe it reduces the timing by allowing the arm stack to go deeper into the magnetic field before the comm segment makes contact with the brush, ergo lower timing. It also increases the pressure of the brush on the comm due to a smaller contact patch while reducing friction due to that same smaller contact patch. The spring can be adjusted to compensate for the increased pressure.

 

With lower timing, reduced spring pressure, and less friction these motors should run ice cold. But not quite as fast as one with all its timing.


Fred Younkin

#13 gotboostedvr6

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Posted 04 April 2015 - 12:58 PM

Fred is correct.
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#14 Mark Johnson

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Posted 29 October 2015 - 06:30 PM

If you keep the unmodified edge as the leading edge you will keep the timing and reduce shorting.

 

Mark



#15 Fast Freddie

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Posted 30 October 2015 - 01:14 PM

Thanks for the up lifting acknowledgements.  I do have a postscript though.  Last year I ran a totally stock (uncut stock brushes and stock springs) 4002FK in the Gaithersburg 1100 and it ran flawlessly.  I did, however, make sure that the brush hoods were perfectly aligned, using the brush wear method.  So as far as I can tell when things are aligned correctly there is no need for cut brushes, I have them if I need them.

 

But wait there's more.  I had a 4002FK that was running very rough and after inspection I noticed the arm was riding on the can bushing.  The arm wasn't centered.  So I took it apart and here's what I found;

-After removing the seal I noticed the end bell was retained by the can/end bell tangs and 4 screws.  I removed the screws and straightened the tangs. 

-The end bell bushing fell out as I pulled off the end bell which, by the way, wasn't glued to the can.

-Once I released the tangs holding the magnets a very gentle tap got the magnets to drop out.  The glue or what ever it is holding the magnets in resembles clear RTV.

This motor sounded like it would run very well so I'm going to, wait for it, blue print the motor as best I can and see how it turns out.  Wish me luck.


Fred Younkin





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