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Old 01-16-2005, 02:02 AM   #1
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Default I keep cremating my comms!

Hey! I am after some help because no matter what i do my comm is badly burnt after each race.
I've been running 7x1 and 8x1 kisbey modifieds (yokomo based motors) and have had similar trouble with Orion V2 8x1 and 9x2.

My lathe work is fine, comes up perfect as can be. I clean the sections of the comm with a scalpel to remove any build up and run a pen down each section gap to fold down the edge. I also give the comm a clean with shellite.

I cant for the life of me get more than one run out of my comm before it's shagged and needs another tru on the lathe. I dont have to take much off the comm, but it's always VERY dull grey colour after a 5min race and looks nothing like any of the other mod racers at my clubs motors. I dont gear the motors very hard or run high timing.

I have been running Reedy Plutonium Long Life brushes ( the silver ones that dont wear at all or become overheated ) .

Any suggestions would be greatly appreciated.

Thanks!

Tim
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Old 01-16-2005, 02:08 AM   #2
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I thought I read somewhere that the new high silver brushes from reedy/cs/lrp/etc will leave your comm a silvery color but it won't hurt performance? Are the other racers you race with using the same brushes as you?
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Old 01-16-2005, 02:16 AM   #3
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they have hurt performance. considerable drop off midway through races. very noticable loss of punch. it's a silver colour, but it's clearly burnt.

it's definately not my cells with the performance drop off. they measured 1.195a.v. on my T35gfx.

where i am there are no other racers using the same brushes at this stage.
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Old 01-16-2005, 02:57 AM   #4
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does the same thing happen with regular brushes?
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Old 01-16-2005, 03:05 AM   #5
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yes though i find with regular brushes the edges of each sector of the comm are more heavily burnt than the rest of it.

with the current brushes, the whole thing is burnt, the edges are the same as everywhere else.
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Old 01-16-2005, 03:42 AM   #6
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Without seeing the motor I can tell you a couple of things to try:

Firstly, how much time is there between when you use shellite and you run the motor in the car? Whilst shellite is excellent as a cleaner, it tends to dry out both brushes and comms and you need to leave quite a bit of time before running the motor so the brushes/comm has time to recover.

Second, how hard are these new brushes and how are they running in terms of heat? If they are much harder you might need to go to a slightly softer spring.

At the end of a race have a look at the end of the brush near the wire shunt as well as along the side of the brush, is it discoloured in any way at these points? If it is then the brush is running too hot - even if you think you're gearing is right try some different ratio's - remember too much undergeared is just as bad as too much overgeared with these low turn motors.

If you still have problems I suggest you use some european sourced brushes (LRP, GM etc) - these seem to have a much higher load/heat tolerance than many US sourced brushes.

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Old 01-16-2005, 03:59 AM   #7
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I have tried LRP's new brushes... similar to CS and Plutoniums with the same result as whats happening now.

I have also used GM brushes on previous motors with similar result, different colour burn on the comm, but burnt to the point that i wouldn't have any performance left if i were to run them for a second run.

The Plutonium brushes haven't suffered discolouring at any time. They appear brand new besides having the serration worn off. They appear to be very hard though. Have suffered virtually no wear from a good number of runs.

The time between using shellite isn't huge. say 25-30mins today at racing where I had slightly worse comm burn then normal. I have always used shellite instead of a motor spray so this is a potential problem. I'll keep it in mind and try it at the next race meet.

What advantage does a motor cleaner hold over shellite?

Thanks for the advice bender.

Tim
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Old 01-16-2005, 04:22 AM   #8
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I don't use r/c motor sprays, I use shellite as well. Just remember that it dries out the lubricant in brushes so if you run the motor after you've just cleaned it then the brushes will overheat.

But you're 30 min gap should be fine.

From what you've said about the hardness of the brushes it would seem this is the problem.

Quote:
Have suffered virtually no wear from a good number of runs
Considering you are running 8 turn motors I would say that such long life shouldn't be the case.
I know these new brushes are designed for longer life, but if you dramatically increase the life of the brush, it is usually at the expense of comm life. If it was me I'd be trying every brush I could lay my hands on until I found one that is more "comm friendly".
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Old 01-16-2005, 04:37 AM   #9
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proberly got dud motors haha
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Old 01-16-2005, 04:44 AM   #10
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what timing are you running?
be careful if you're setting the timing off the stickers on the motor as theyre often a long way out.

not overgearing?

is there any binding anywhere with the car?
including being sure sure that the bearings on the motors are also smooth, not being pinched, etc.
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Old 01-16-2005, 04:47 AM   #11
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I run 9 or 12deg on all my motors for starters.


Mr Barracuda, piss off until you have something decent to post.
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Old 01-16-2005, 04:54 AM   #12
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Check your esc's drive frequency also. If it is set in one of the lower frequency settings (like for stock racing to get punch) you can burn down motors that way too.
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Old 01-16-2005, 04:54 AM   #13
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I have a GM SX9.

What should it be set at?
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Old 01-16-2005, 04:55 AM   #14
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with timing i'll start at about 6 with my 7t v2's and then add 1mm of timing per wind from there... works out to about 10 an 8t and so on.
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Old 01-16-2005, 06:20 AM   #15
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Just a few ideas....

Have you run your motors really hot?
Once you heat you motor badly, it always seems to affect com life from then on...

How do you use your throttle?
Particuarly on open tracks or on foams, its easy to hit the gas hard too early in a corner and put heaps of load on your motor.

Timming?
As stated above, timming marks on motors are not always right.. Get something to check it with.. low is a good starting point...

Drivetrain?
Remove your motor and check this... I run a 415 and have wasted heaps of bearings in my uprights. Cause I am too lazy to change em, I run the car anyway.. Makes a big difference to motor life between rebuilds...

Schotty diode?
Do you have one? they seem to make everything last a little longer, esp if you use brakes...

BTW: usually drive freq of around 6k is a good starting point if your speedy can be setup like that.
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