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  #1  
Old 09-20-2013, 02:44 PM
NCSS NCSS is offline
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Default Mega G motor brush replacement

So I finally had to replace the motor brushes on one of my Mega G cars.

I ordered AFX brushes and springs from Lucky Bob, a great guy. I ordered 5 sets so he called me and suggested the 5th set of brushes be Wizard WS02, which are copper and would work. (The AFX ones were in packs of two pairs.) The AFX ones are carbon.

Not only was Lucky Bob correct, after fooling with the carbon AFX brushes working and then not working, I tried the Wizard brushes, and it works like a charm. The car ran very well through about 20 test laps with the Wizard brushes, very steady.

Can new carbon brushes foul the commutator ? I can't for sure figure out why the car would work well for a while with the new carbon brushes and then quit. I cleaned the comm with isopropyl alcohol, maybe that's leaving a bit of a film?

Any potential drawbacks to using a copper brush in a Mega G? Heat?

Thanks.
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Old 09-20-2013, 05:45 PM
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One thing you need to understand about electric motors, there is a gap between the contact path which is there for a couple reason. First is it creates separate circuits, and second it is designed to shave off the ends of the brush every time they pass over it. The dust has to go someplace. In other applications those plates are sometimes polished so that things do not embed and to create the maximum contact area. I assume that comm polishing on a slot car does the same.

Your question about new brushes might be because new brushes are flat so they have less contact area, but are longer and have more pressure. Once they wear down to shape they have a better contact profile but are now shorter, so have less pressure. Long and short is that even though the shape is better it is bouncing off the comm more and providing less positive contact. Or maybe not......

I fixed this situation with adjustable brushes, but many people have suggested slightly larger brushes.

http://slotcarillustrated.com/portal...t=mega-g+parts
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Old 09-20-2013, 07:01 PM
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Default Thanks for the info

Thanks for the info and link. Just trying to keep a small stable of Mega G's running well for neighborhood/friends slot car parties this fall. At least I can now replace the things. Whomever once suggested doing it over a tray or tupperware container gets my thanks. Only lost one brush spring. ;-)
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Old 09-21-2013, 06:53 AM
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As far as I know most of the motor brushes that are used today are a carbon/copper composite. Aftermarket brushes tend to have a higher percentage of copper, I believe that the Wizzard brushes are 80% copper. With inline cars, such as the Mega G, new motor brushes should be broken in before you apply full power to the car. I run in new brushes at 3 volts for 30 minutes. I flush the dust out of the commutator slots with contact cleaner, oil the bearings and then run the car on the track. If you run new brushes at full power you can damage the commutator . If there is dust in the commutator slots that can short the comm and it can get hot enough to melt something. That is much more of a danger if you have a big power supply. With wall wart power supplies, even if you have one per lane, the car will just slow down, but will usually not be permanently damaged.
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Old 09-21-2013, 03:05 PM
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Quote:
Originally Posted by RichD View Post
As far as I know most of the motor brushes that are used today are a carbon/copper composite. Aftermarket brushes tend to have a higher percentage of copper, I believe that the Wizzard brushes are 80% copper. With inline cars, such as the Mega G, new motor brushes should be broken in before you apply full power to the car. I run in new brushes at 3 volts for 30 minutes. I flush the dust out of the commutator slots with contact cleaner, oil the bearings and then run the car on the track. If you run new brushes at full power you can damage the commutator . If there is dust in the commutator slots that can short the comm and it can get hot enough to melt something. That is much more of a danger if you have a big power supply. With wall wart power supplies, even if you have one per lane, the car will just slow down, but will usually not be permanently damaged.
Good points. I did some break-in using Tri-Power Pack on low. The car will run like a champ for a while, then just stop. And it does seem hotter than normal, so I've cleaned out the comm slots using a toothpick. Thanks! Learning yet more from you guys...luckily in a way this particular car was always a dog, so if it can run well for short periods eventually I should be able to get it running well for long periods. Or so I tell myself. ;-)
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  #6  
Old 09-26-2013, 05:54 AM
Eric Peterson Eric Peterson is offline
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Make sure nothing is binding.
The fact you said the car runs well and then slows down,
I do not think its your brushes. Could be a weak brush spring, when hot it goes soft.
The car should warm up to operating temp and run all day. That is not what you described, yours runs warms up and stops.
You have a heat issue.
Like rich said, low power out put from wall warts won't let you burn it up to damage.
Put that car on a big amp supply you will be able to bake pizza.
Look at the pinion, with my mega, I saw the pinion more or less held the arm for spacing. Make sure there is no friction in this area.
Bad gears can make heat
soft pick up tension, whilst the tension needs to be stiff because neo tractions are used with this car.
What comes with the mega is all over the place mostly being to stiff but I wouldn't rule out being soft.
Tire rub.
Check all your friction points. Check them when cold check them hot. Are they the same?


Something else
Whilst parts are interchangeable, they are not the best.
If given a choice I will always use what is made for that car.
In the case of hop up parts in the kit, well that is a waste of money.
With brushes and springs, using anything other than stock parts is a major improvement but, it changes things.
Everyone will tell .006 springs are the replacement, it works. Yeah but is it the same?
I think mega springs are made from all the late 70 steel china was selling to US auto makers, wasn't so good then ain't no better now.
With putting quality brushes and springs are what is needed, you may have to much tension on the comm .
Use a smaller brush length to relive some of the tension.
When you spin the wheels by hand it should continue to spin a bit, to free wheel.
If you spin the wheels and it stops right away, to much tension and it will make heat not speed.

Last edited by Eric Peterson; 09-26-2013 at 08:25 AM.
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  #7  
Old 09-27-2013, 12:10 PM
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Default Indeed

At this point it's easier to list the things that are not new on the car in question: the armature and bushings, and the chassis. I see your point about brush barrel springs, and did change one of those out as that one seemed weak. (I've been stockpiling spare parts for two years now.) ;-)

Intuition at this point tells me to check for binding on the commutator . Everything seems to spin as well as any of my other Mega G cars at this point, and I made sure the rear axle assembly and pinion mesh nicely. When I get around to it I may just put the AFX carbon spring back in and see how that goes.

If nothing else I've learned more about these particular slot cars, and as I mentioned that particular car had always been a dog anyhow. Kind of wonder if it was one of the "premature brush wear" ones people sometimes talked about.

No big deal, learning is good. Thanks everyone! I still have plenty of cars and spare parts to host some slot car parties this fall, so it will still be fun!
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Old 09-27-2013, 01:32 PM
Eric Peterson Eric Peterson is offline
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Get rid of that arm.

Check the ohms of that arm.
It was posted a way back the ohms are low and can vary with MG arms.
MG arms
These are not custom arms, a low ohm reading in my opinion is trouble. It will go like stink but the extra revs and heat created could be eating them up from the inside. Its a stock arm.

What your looking for...
one bank will be far off from the others on ohm readings.
If that is what you find out, you found your answer.
Eric
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