# Dot commutator brushes



## back.to.ho (Jan 3, 2012)

Question - does anyone:wave::wave: make a performance, or better grade of Dot commutator brushes for magnatraction type chassis ? Thanks for any info.


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## beast1624 (Mar 28, 2009)

You can probably find some that will fit at this site (they have every size and shape imaginalbe):

http://www.kjmagnetics.com


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## Boosted-Z71 (Nov 26, 2007)

I dont think he is talking about magnets, I think he wants motor brushes, I have used JB, & Wizzard brushes in many Magna-traction chassis, The dot on the bottom is really there just to help you install them & the top plate easier. The wizzards are a little easier to install as they are just a little shorter than the JB brushes. The trick is to get the height correct to avoid to much spring pressure on the com, I sand the brushes on 1000 grit paper on the bottom side if you need to adjust height. 

Boosted


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## back.to.ho (Jan 3, 2012)

Thanks Boosted, t-jet brushes will work.


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## beast1624 (Mar 28, 2009)

Sorry, should have read all the way through.


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## Ralphthe3rd (Feb 24, 2011)

*Brush height ?*



Boosted-Z71 said:


> I dont think he is talking about magnets, I think he wants motor brushes, I have used JB, & Wizzard brushes in many Magna-traction chassis, The dot on the bottom is really there just to help you install them & the top plate easier. The *wizzards are a little easier to install as they are just a little shorter than the JB brushes*. The trick is to get the height correct to avoid to much spring pressure on the com, I sand the brushes on 1000 grit paper on the bottom side if you need to adjust height.
> 
> Boosted


Ummmm....I thought that the Wizzards were Taller than the JB's !
BTW- you also have the option of the NEW Slottech Brushes as well.


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## Boosted-Z71 (Nov 26, 2007)

I checked my stock, and all of the JB's are taller than the Wizz brushes, some as much as .020. I dont have any of the SlotTech to compare too, so I cant speak on those.

Boosted


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## slotking (May 27, 2008)

http://www.hobbytalk.com/bbs1/showthread.php?t=362584

this may help as well


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## JVerb (Oct 6, 2006)

*brush height*

I have found that magnatraction chassis are very finicky about brush heights. The chassis that I am running now has a set of brushes that were sanded down and look like slivers compared with wizards, slottech or JB’s. This car with tall brushes was very hard to drive but was a rocket on the straights. The car was wide open or stopped regardless of which controller I used. When I changed to the short brushes the car was very drivable with a 45 ohm controller. I hope this helps you find a solution.


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## slotking (May 27, 2008)

there is a little play room on how you setup the spring arm.
as well as how you use the springs. 

because we raced poly mags and any arm we had find the sweet spot.
with the stock brushes i often used 2 springs with 1 cut down some.

with the after market brushes, I used 1 spring and sometimes cut it a little short.

or i may bend the bottom spring tab a hair down to lighten tension.

you do not want the car kicking out when you brake and some slow to get around the turns


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## Bill Hall (Jan 6, 2007)

So long as you can get the lid on and things dont lock up....go for it!

It's all about clearance Clarence. 

Due to the design change from the lever style T-jet brush spring; the Mags and pancake Xcellerators, use a beefed up perch and a coil spring. The Super ll uses an actual guide. They are all susceptible to coil bind if you're not paying attention when shuffling different springs and brushes around. 

If pressed, the early lever spring just bellies out below the chassis. They give. Conversely, due to the later re-inforced spring perches, the later style coil spring's travel is finite. The end result of compromising brush travel mashes the top armature shoulder into the bottom of the gear plate if ya get too pushy. Coil bind IS arm bind because the entire package moves in unison on the vertical axis. It's an inherent quirk of pancake style E-motors with horizontal comms. As you load tension into the comm springs you load equal tension into the opposing bearing surface.

The idea of calling arm bind "brakes" is one of those nonsensical slot car terms. It's not brakes... but it is like driving with the E-brake on at all times. (Just ask my wife....LOLOLOLOL) Irrespective of what comm spring design is used on a pancake, the turn of the trick is to find the maximum amount of spring pressue for good current path, but not so much that the upper arm journal becomes a grist mill. 

Regardless of what combination you use, the armature must have some USEABLE end float. When assembled, the brush pack pushes the arm up and exposes the gear to plate clearance topside. After set-up, and prior to applying power; you should be able to finger poke the gear and feel the springs doing their job. Naturally with tighter gear to plate tolerances, and hot rod parts combinations you have to utilize some common sense.

All in all, a better mouse trap IMHO. Although there's less margin for error, it's pretty hard to screw one up unless your not checking your work.


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## slotking (May 27, 2008)

the term brake is used because the car stops faster.
High tension on the comm is used for both brake and top speed.


your right about the AFX mag and having to much tension can cause binding because there is little spring flexibility.
I used to cut my brush springs to work with the JB brushes in my AFX MAG

the t-jet and non-mag are more forgiving.

btw, I have some old MURA V cut brushes and they they really set up high in the t-jet and non mag afx


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## Bill Hall (Jan 6, 2007)

The term is stoopid


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## ajd350 (Sep 18, 2005)

Agreed. It's not brakes, its.....


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