how often should i replace brushes??

[littlemaf]

could someone tell me how often i should replace brushes in my motor? i've heard some poeple say they replace them after each race, but i know that isn't neccesary. i have a kyosho x-speed 15t motor, and race most weekend at which we have 4-5 races which last about 5 minutes. i haven't staretd going to any national ones yet but hope to in the near future, so i want to know everything there is to know to keep my car/motor running perfectly all the time.

[marcoski]

You should skim the comm on a lathe every three runs, you will only need to take off a tiny amount, but the comm will last MUCH longer doing it this way rather than allowing it to become grooved and badly under cut.

Brushes should be replaced when they become discoloured, or too short, but in any case after four skims.

[Doughty]

I have never found my motor to be any good using used brushes on a freshly skimmed comm.

I always skim/brush at the same time. on high grip tracks at big meetings I skim/brush every 2 runs, every 1 run if the motor is not that happy.

(this is all based on off-road racing)

[DA_cookie_monstA]

I agree, it is a false economy to run used brushes on a fresh comm, but I think everyone got their own opinion on that.

As for the periodicity of the skimm, that ALL depends on the state of the motor.

[marcoski]

I think that rather depends on what level you are at. I accept that at the top of the sport (Chris) you will notice the small benefit of a rebrush every skim, and a skim every run, BUT for lesser mortals, that is outrageous and expensive. A youngster and average clubman like littlemaff cannot justify nor afford this level of replacement! Hell I have plenty of cash, yet when I was running brushed, the brushes got changed when they were too short (about 2/3rds full length) and I never really noticed a loss of performance. I could not justify throwing away what to all intents and purposes was a new brush! Mind you I never tuned to nuts off my motors and the brushes were not exposed to so much stress, also I pretty much always used a 17 turn motor with 12 degree timing. All very low stress. Also, when skimming every three runs, I only used to take 1/100th of a milimeter off the comm, such a small change in diameter would in my opinion have no effect on the contact patch of the brush face, and it would very quickly bed in. Its horses for courses, and IMHO the top level regimen you describe is way OTT for us B final bobs!

[PDW]

I agree with Chris, as a B Final Bob!

Much of the problem stems from people running too much timing. Run the motors at 5 to 8 degrees; gear to keep the motor gently warm. If you need more power, then go to a hotter motor.

Yes, I know that if you are running 12-turn at National level, then you need every last watt of power, and so screwing the timing up gets results. However, so does a mild timing and higher ratio and a sparing use of the throttle.

So I set my cars up with mild timing, higher gear ratios and use the throttle sparingly. I rebuild every other meeting (Touring Car) for 12-turn, and every meeting for 19-turn. I find that re-using brushes accelerates comm wear because the natural lube in the brush dries up, and wears the comm faster.

I don't understand why people will not accept that £4 per meeting for brushes IS the cost of running motors. Mine last until the comm has no copper left. Overall, my spend is less because I don't ruin motors. Rebuild regularly with new brushes is my advice.

People rarely think twice about buying more cells, more tyres, more motors, but get really narked about a £4 set of brushes each meeting. Penny wise and pound foolish??

[Oscar]

Surely the number of turns of the motor has a bearing on the time intervals between re-brushing? Whilst I'd not consider running an 8 turn for more than say 2 runs on a set of brushes, with a 15 or 16 I'd feel confident running the same brushes for 5 or 6 runs. I would also apply similar logic to the frequency of skims.
Does anyone agree ??

[PDW]

Nope! If the 8-turn is set to burn out brushes in two runs, it is not following my "rules", it has been timed up, or geared incorrectly.

The comm wear is not related to the current passed, it is related to the heat generated and the amount of sparking. Run on a low timing angle, it should not spark. Correctly geared it should not get hot.

My suggestion is based on the fact that most of the time on most tracks you can't use full throttle. If you do, all that is happeneing is that exces current (energy) is turning to heat (energy) and the advance makes the brushes spark at high speed. Similarly, hacking on the brakes makes the motors spark.

Try to put the motor building regimes of the top racers in perspective. They CAN use all that power, so a rebuild every run of a motor timed to the limit gives them an advantage. Since most of us cannot do that, there is no reason to increase timing and so the motor goes well for longer - be it a 19-turn or an 8-turn.

[littlemaf]

Hell tis quite a job keeping up these motors aint it lads..lol. so i should replace brushes and skim the comm one after each meetings definately, else i'll end up loosing power and messing up my comm?

<language !!>

[Mark Stiles]

Stick a nice little mabuchi 540 in you car. It'll be faster, honest! (I might find it easier to win races then!) ;D

[littlemaf]

well i'm giving this one a chance first. inonly got it at christmas!

[PDW]

Matt, if you run your 15T on a low-ish timing, don't abuse the throttle and check it after every run, then I'd say that you should notice some brush and comm discolouration (that you can't remove with a comm stick) after about 8 to 10 races.

Skim it. If you took off micro amounts, run it for 12 to 15 races. If it was in poor shape, stick the the original interval (8 to 10). And I am with the "new brushes every skim" brigade. However, look at this thread too:

http://www.rcracechat.com/forum/index.php?board=7;action=display;threadid=7393;sta rt=0

as you might like to try these products to reduce cost. HTH :)