Brush problems/questions

[FilthyPierre]

Ok, I've had it. Last weekend I decided to try some new trinity e-brush 4499's in my P2K. I didn't cut the comm, but it had been only cut about 10 runs before, and was still nice and clean and (as far as i could tell) round. I also used the same gearing on my XXX as I always do - 82T spur, 21T pinion.

The car went well for the first race. Second race, I was out in the lead by a fair distance, when all of a sudden on the last lap, the car slowed notcably, barely getting across the line (just got home to win). So, I pulled the motor out and apart, sure enough the comm was burnt, but only one brush was black. The serrations hadn't even worn off, so the burn marks on the comm were stripes. A similar problem happened a few weeks ago when I tried some Reedy brushes.

Later, one of my clubmates told me that I shouldn't use those high-silver brushes until the final - basically that they're single use then-you-gotta-cut-the-comm brushes.
So why on earth to Trinity put them in their Pro stockers, and I also notice that reedy put the 767's (competition brushes) in their new MVP stocker.
Nairb, XXXER, you guys use the 767's - are they high silver single-use ? How many runs do you get out of them ?
Anybody else use 4499's ?
Should I gear down even further when using them ?
Finally, what's the best brush to use then that doesn't destroy your comm ?
Thanks.

[Isky]

you are over geared...way overgeared. Go down on the teeth on the pinion by atleast 1 tooth.
-Isky

[Grizzbob]

Well, really it's a good idea to change the brushes out at least every 4-6 runs, for the comm's good more than the brushes. Even after a couple of runs, the comm can get out of true(for lack of a better word), & every run will do more damage to it with any brush, but especially high-silver content ones. That grows exponentially, so the more runs you do without retrueing the comm, the more damage you do to it. That's why many racers recommend changing the brushes fairly often & trueing the comm every time you change them. Doing it, say every 4-6 runs or so really does allow the comm to last longer than doing more runs between cuts, because you don't have to remove as much material from the comm when you do it mmore often. As for 767's & 4499's, I actually like both. For some motors(like the older Yoks, the Rage being one) I prefer 767's all-around, but I've also gotten good results from using 767's on the + side & 4499's on the - side of motors like the Green Machine 3, it seems a good equivalent to Trinity's polarized brush setup, & it does work pretty well...... http://www.rccaraction.com/ubb/smile.gif

[Railman]

Filthy Piere: It sounds like a brush hung up on you. It's the only reason I know that cause just one brush to smoke. On another note it is generally bad prctice to change brush's other than when you cut the com. The combination of lost material @ the leading edge of the com & breaking in brushes @ the same time will cause excessive arcing. As far as the E brush is concerned It is probably the best choice for making power, but you need to cut the com about every 8 to 12 runs. You can go more but you will need to take a lot more off @ each com cut. It's like this: .002" every 10 runs or so, Or about .010 every 16 runs or so. It will run better & last longer the more often you cut it. We usualy re-sereate the brush's @ each com cut, because some of the silver seems to transfer off, leaving some oxidation on the leading edge. Re-sereating will give new performance again. I can run the same brushes for 20-30 runs maintaining in this way on a P2k. I myself also like a small slot @ the center of the brush (parallel with shaft) for a few more rpm. Hope this info/opinion is of some help. Have fun
Racing!

[Railman]

Grizzbob You type faster than I do! I think we pretty much agree in principle only the numbers change. I have three boys + myself to keep in brush's & we tend to make them go a little farther than some. WE keep a sereator setup & find it easier to cut than to change. As far as the gear ratio a 21 pinion sounds about right for a P2K for a 60->80 ft. staightaway. For 80-> 100ft I would go to a 22 tooth pinion. It should still run cool for you without any problem.

[FilthyPierre]

Thanks for the info guys, muchas grassy arse. However, I have a couple of other points. When using brushes of less silver content, I can get a good 20 runs out of a comm cut and a pair of brushes. I always clean the comm and brush faces (using a trinity comm pen, and comm sticks, and brasso). It only seems to occur when I use the high silver.
The previous time this happened (with the Reedy brushes), it was also only one brush that burnt. That time it was a fresh cut (in fact, a brand new diamond-trued Pro arm) and a new set of Reedy brushes.
I've been using the same pinion/spur combo, even using a 23/82 without any probs (except that the car was a little slower off the mark).
I usually don't change brushes unless I get a comm cut, but I don't own a lathe so sometimes it's difficult to get a cut when you need it.
So, sorry if it seems I'm a little slow on the uptake, but you're saying that I should get at least 8 to 12 runs out of a set of 4499's or 767's ?? Do you think it would make any difference if I gear down a tooth or two when using them ?
Anyway, it looks like I'll have to go the $330 for a lathe, at that price I only have to cut my comm(s) 66 to 110 times to get the money back. Bargain. http://www.rccaraction.com/ubb/smile.gif

[Grizzbob]

$330? You don't need to spend that much on a lathe, there are plenty of good ones that can be found for about $150(the Cobra one even comes with a diamond bit at that price), & they'll work fine. For power, a power supply may be best, but for the time being, you can do fine with a 4 cell pack(I simply removed 2 cells from an old pack I don't race anymore). Oh, just to clarify, you can actually do more runs on a pair of brushes, but 4-6 is about where the performance starts to fade(according to my lap times & dyno results), & I don't consider any more runs simply because I don't yet have a serrator, I just go by when the performance drops off. It's true that as long as you don't burn the brushes from overgearing, then you should be able to reuse them quite a bit..... http://www.rccaraction.com/ubb/smile.gif

[FilthyPierre]

Grizzbob, this is Australia the sunburnt country, land of sweeping plains, land of strange animals, the most overtaxed country in the world, and land whose dollar isn't worth a pinch o' shite.
So $150 USD is about $310 Oz at the moment.... I was just quoted $595 for a Hudy Advanced lathe, with diamond bit - this is about $250 US at Stormer, so about $510 if I order from them.... so $330 for an Eagle lathe with carbide bit (I can buy the diamond later or resharpen the carbide) sounds pretty good....

One other question - I thought serrations on brushes was to help them break/bed in. So why pull used ones out and re-serrate them ? Does it help power, or increase their life span ?
Thanks.

[Railman]

Filthy Piere, No need to go overboard on the lathe. We have a third hand Cobra that we bought used for $40, came with a diamond & carbide bit. The diamond bit looked good & seemed to cut ok, but upon inspection with a hand held scope prooved to be chipped. The man that designed the P2K (Jim Green), as it turns out uses an old Cobra, (no ball bearings) with a carbide bit, because he has had the same problems with diamond bits chipping. The ball bearings, in my opinion, only add another element of runout to the tolerance issue. Ball bearings are good for static balancers (low friction), but not for reducing runnout. We have cut about 50 to 100 coms with a carbide bit, that was used when we got it. I just touch it uo with a diamond hone now & then. We're only cutting copper! I highly recomend picking up a small hand held scope, 35x or so( $10+-@ Radio Shack). Many RC motor, gear, etc issues make a lot more sense when you look at what's happening up close. Shiny don't mean everything. The brush serrating thing was expained in my 1st post. It seems like these motors run best right before they need to be cut because there is a little bit of brush float, which reduces friction, but still have good enough contact to transfer the juice to the arm. However this condition is short lived & a silver brush don't hold up to a lot of arcing. The serrating removes the oxidated surface of the brush, & allows renewed performance. Serrated brushes break in quickly, & reduce friction. All of this info is just my opinion & I would like to invite others to discuss also.

Been thinking about just the one brush smoking, was it on the + or - side? Might be just a bad spring? If overheatd one time it could cause this. Just food for thought.

[Grizzbob]

Sorry about that, Pierre, I didn't think about costs outside the U.S.(bad habit of mine), but I agree with Railman, you still might be able to find a used one for a good price. I also agree with his opinion on serrations, they do help keep friction down for awhile, & help give you that balance of conductivity/friction..... http://www.rccaraction.com/ubb/smile.gif

[Nairb]

Pierre, these guys have given you some good advice. Sorry for taking so long to answer, I've been to busy to check the forum lately. Both the Reedy 767s and Trinity 4499s are good brushes for stock racing, even if they're a bit hard on the comm. I have noticed that the 767s are softer than the 4499s and they break in faster; I also think that because of that, they wear out your trued comm faster and it must be re-trued sooner. Whoever said that you should run these brushes only once and replace them is high on buggy grip. That is way too excessive in my opinion. Sure, you could get maximum performance by cutting your comm and replacing the brushes every race day a few times, but it's not needed and way too wasteful. I go about 3-5 race days with a fresh comm and brushes before I rebuild my motor and I don't see much of a performance drop at all. Sure, I could run the same brushes without cutting the comm for months without burning them up, but for maximum performance comes from keeping your motor in good shape by cutting the comm and replacing brushes sooner. I totally recommend rebuilding your motor often, but don't waste your time and money by doing it too often. As I said, I think every 3-5 race days is adequate. Just take the time to inspect your motor and you decide when to do it. You decide when it's worth your time and money to regain maximum performance.

With all that I've said, I don't think you should be burning brushes and comms with that setup. Your gearing sounds fine for a buggy, but try going down a bit more and see what happens. Try to keep your motor happy (not overheating by overgearing) and you'll be happy. I think the problem probably had something to do with insufficient contact between the brush and comm. That spring could be screwed somehow, but, more likely, there could be something in the brush hood causing too much friction and not allowing the brush to be pushed all the way to the comm. Check the brush shunt. In your solder job, did you leave enough slack for the brush to move in and out of the hood easily? Is there too much tension acting against the spring? Concentrate your efforts on the endbell; I think the problem is somewhere therein. Good luck!

[FilthyPierre]

Thanks again guys. Well over the weekend I went and bought the Eagle lathe. I'll put in another post for help on that....

Nairb, I figured you were getting more runs out of a set of brushes. 3 to 5 race days is what I was getting out of the other brushes.

The dude who told me one race out of a set of silver brushes, in all fairness, didn't know what sort they were, I just told him high silver. And he's helped me transform my XXX from an uncontrollable heap into a winner so I figured he knew a few things.
Anyway, that aside, you could be right about the endbell. I made sure that the shunt wires were long enough and wouldn't snag, I made sure that the brushes were hard against the comm etc. It's possible that the brush that burnt (the +) was slightly hung... I've also been using harder springs than standard, another friend told me to go back to the original P2K springs when I put in the 4499's. I'll put the bell apart and see how I go....