# How often do you cutt your comm?



## Dustin (Aug 9, 2004)

Hey Guys,

I run a Trinity monster stock in my MF2. I race once a week on saturday, and on that day I have 4 races on the motor. I know guys who cutt there comm every weekend, every other weekend, every three runs, ect........... How often do you think I should cutt mine?  

-Thanks for any help

-Dustin K.


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## tfrahm (Nov 14, 1998)

Sedan and Oval -- after every day of racing... (No more than 3-4 runs)
Offroad -- Stock motors go 2-3 days of racing, Mod every race day...
12th scale -- after every day of racing...


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## hankster (Jan 1, 1998)

I would say it depends on the brushes you use. On my off-road stock motors with Putnam brushes I need to cut the comm after 2 runs. The Orion V2 motors can go 10 to 12 runs before cutting. Best way to tell is to look at the comm for any burning.


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## Guest (Oct 24, 2004)

It depends on brushes plus how agressive the setup was in that case it may be only one run. But for 6cell racing probably 4 runs max, in 4cell racing about 6 runs. I still use a comm stick and motor cleaner after each run until comm needs to be trued.

For racing I generally have about 3-4 good race motors and a couple replacement armatures. Older motors may be used for practice with one close in power to get vehicle setup for race trim. Having a couple extra motors allows you to have a fresh motor without the need to take extra equipment reducing wear a little to motor.


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## baih (Sep 26, 2001)

i use two motors. one motor two practice runs and a qualifier. second motor one qualifer and then the main. cut comms after each. your brushes will make the difference on how often you cut your comms. 

use a comm stick after each run. you still will need to cut the comm as soon as the surface shows wear.


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## Slider (Dec 7, 2003)

I personally cut comm after 2 runs no matter what.I want the most out of a motor.4 cell is a bit more forgiving.But I Don't go over 2 Heat's But as said above, The type of brush makes a big difference on when to cut a comm. If you cut one sooner.it will remove less material than letting one go longer.Objective keep it Fast and fresh. On the Plus side of cutting one sooner will help eliminate possible glitches.


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## Dustin (Aug 9, 2004)

So.....will cutting your comm every 4 runs put more wear on it that cutting it every 8 runs?


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## RCRacer45s (Oct 22, 2002)

I cut mine after every run and replace the brushes sometimes if i know the certain motor will run better the second time i will leave it alone. I run 4-Cell stock on oval.


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## David Washburn (Aug 26, 2004)

Dustin said:


> So.....will cutting your comm every 4 runs put more wear on it that cutting it every 8 runs?




no cause if u run it 8 rund u put a dip or valley in the com and the u have to cut more off of it
:thumbsup: :thumbsup:


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## Dustin (Aug 9, 2004)

Ok guys,

How many times can you true a comm before you need a new arm?


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## RCMits (Jan 1, 1970)

it all depends...

check the com after every race. if it looks dirty, or a bit pitted, its time. first though, try a com stick to clean up the face, a lil spray to clean it up. sometimes you cant get your comm cut after racing during the day.

you CAN last a whole day racing on a set of new brushes (depending on brushes) and just clean the comm at the end of the day. i know people that can go 3 weekends w/o cutting and they do just fine.

me, i used to go every weekend, and cut maybe every other weekend. i do have 5 motors though, that if they look like its time , i swap to a fresh broken in motor.

if you have a comm cutter, and you have the time.. it dont hurt to do it..

competition level, at a big race, id have a clean comm for each run.


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## RCMits (Jan 1, 1970)

ps..

buy a big jim motor book  its got lots of usefull info


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## David Washburn (Aug 26, 2004)

Dustin said:


> Ok guys,
> 
> How many times can you true a comm before you need a new arm?


id say about 6 or 7 times max before it loses power or starts to peel up 
:thumbsup: :thumbsup:


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## XXX-SCapece (Apr 28, 2004)

Never go more than 1 run in off-road. Dirt will wear down the comm and slow you down. I'll cut my touring and off-road motors after each run. It will make the motors last much longer. On the other hand, if you get and Orion V2 w/ enduro brushes you can go atleast 20 runs before you need a new cut, and the brushes will last you 30+ runs. :thumbsup:


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## Slider (Dec 7, 2003)

Dustin Most stock motors. when you get it is around .295 the comm. you can use it till you get to around .270. after that it is about time to pitch it in the trash.and get a new Arm.or motor.


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## integy racer (Oct 24, 2004)

For oval i normally cut it after the race night, but if i see it slowing a little i will cut it than, but for off-road i normally do it after about 4-5 runs on the motor.


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## sean cant drive (Feb 22, 2004)

do high or low copper brushes wear the comm more?


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## BrentP (Mar 1, 2002)

I only race oval, almost all on carpet. I run mostly monster's with 767's. For weekly club racing I can & do go 4 to 6 runs on a motor before cutting the comm. Although, when I am at a big race I cut & re-brush every run. On stock motors I throw the arm away when the comm gets to or below .270. I have found anything below that & the copper is so thin that it overheat's & falls off too much before the end of a 4 minute run.

__________________
Brent Pearcy
Bulit Motorsports, TQCells


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## Dustin (Aug 9, 2004)

Yeah,

I could probebly go a while on my comm. But I must have not been very specific when I said I race offroad, because I race indoor stadium on carpet. :thumbsup:

Sorry about that.


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## Slider (Dec 7, 2003)

Dustin Then that put's you running 6 cell.which is harder on the comm than 4 cell. Keep it simple cut every 2 run's and be done with it.Everyone has different reason's of why and when to cut. If you want to be fast do it often. If you want to be just OK.then do it when you want.A fresh motor is a fast motor. I will retire from this as it is going nowhere.


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## David Washburn (Aug 26, 2004)

i agree with slider


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## BrentP (Mar 1, 2002)

Slider said:


> ........Everyone has different reason's of why and when to cut. If you want to be fast do it often. If you want to be just OK.then do it when you want.A fresh motor is a fast motor......


Not necessarily, on the 5th run of one of my monsters last weekend I ran 1 second off the track record at Fastlane in Blue Springs MO. There is some pretty good competition at this track especially that night. I ended up qualifying 2nd over all (out of about 20) with that very run. I cut the comm on Sunday & it only took 3 (.001) passes to clean it up.

__________________
Brent Pearcy
Bulit Motorsports, TQCells


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## ovalnator (Sep 26, 2001)

dirt oval: every 5 runs for stock, every 2-3 runs for mod
carpet oval: after every run (stock and mod)


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## Harlow (Mar 17, 2004)

How many have actually dynoed the difference between a freshly cut comm and one with a lot of run time on it. I never did until I was testing our CommSleeves for durability and found a Reedy KR 12x1 with 40 minutes of 6cell run time on it produced only 1.4 watts less average output than the same comm when fresh cut. That surprised me. I would have expected a 6-8 watt drop. I hope to try this again when I get more time. Maybe comms don't really need to be cut that often. It seems that if the leading edge of comm plates deteriorates somewhat than the flow of electricity from brush to comm plate would be a more gradual process, as the conductivity of the comm plate would increase the further the brush got onto it. Would also be interesting to see if when cutting the comm, don't cut it until it is completely fresh but rather leave some of the deteriorated area on the front of each plate. Just a thought

Test was done on a TD45. You can see the results at the link below. 4th test from the top.
http://www.fussybrush.com/comm sleeve tests.php


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## RobRacer (Oct 13, 2004)

*A com stick - Not.*

I'm confused. I race with one of the best motor builders in the country and he tells me that you should never take out the brushes and use a com stick.


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## hankster (Jan 1, 1998)

While I agree for the most part, if you take out the brushes and use a comm stick, you should then reseat the brushes by running it at 2 volts for about 30 seconds.


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## BrentP (Mar 1, 2002)

Harlow said:


> How many have actually dynoed the difference between a freshly cut comm and one with a lot of run time on it. I never did until I was testing our CommSleeves for durability and found a Reedy KR 12x1 with 40 minutes of 6cell run time on it produced only 1.4 watts less average output than the same comm when fresh cut. That surprised me. I would have expected a 6-8 watt drop. I hope to try this again when I get more time. Maybe comms don't really need to be cut that often. It seems that if the leading edge of comm plates deteriorates somewhat than the flow of electricity from brush to comm plate would be a more gradual process, as the conductivity of the comm plate would increase the further the brush got onto it. Would also be interesting to see if when cutting the comm, don't cut it until it is completely fresh but rather leave some of the deteriorated area on the front of each plate. Just a thought
> 
> Test was done on a TD45. You can see the results at the link below. 4th test from the top.
> http://www.fussybrush.com/comm%20sleeve%20tests.php


BINGO!!

I've found the same thing. That stock motor that I was talking about earlier only dropped 2 watts total on the Fantom dyno.

__________________
Brent Pearcy
Bulit Motorsports, TQCells


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## erock1331 (Apr 1, 2002)

Another thing to consider is how you run your speedo.

If you use a Quantum on Punch setting #5 (agressive) you will need to cut the com more often.

If you run a Keyence, GTX, etc with the drive frequency on say 1.5-2.0 you will need to cut more often than running it at a higher freq.


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## CornwallRC (Jul 4, 2004)

I've seen Top drivers run 1 motor all night at big races running 4 cell Oval... I've been told by many that if the motor is kept in Clean condition you can run it upto around 15 times before a rebuild and cut... I do mine every couple weeks.. Although I have a couple practice motors and 4 race motors...
James


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## Fl Flash (May 1, 2003)

I turn my comms after four runs ( 4-cell stock oval ) no matter what! If I wait longer the pitting in the comm is much deeper so I have to take much more off the comm thus shorting its life. The performance seems to start falling off after 4 runs also. Slider is correct new comms are around .295 and can be turned down to .270 with no problems. :thumbsup:


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## Stealth_RT (Aug 5, 2002)

When I run low turn mod motors, 7-9, in TC, I cut the comms after every run. Unlike Trinity or Epic mods, my Reedy Krs are easy on brushes, so I can get 8-12 runs on one set of 766 brushes. Can't wait for Reedy's new 40 run brushes to come out!


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