Where can I find *hard* brushes?

[fyrstormer]

I've got some low-turn motors in my RC fleet (11t and 12t), and since I'm not racing and don't need ultimate maximum performance, I'd like to use hard brushes in those motors so the brushes will hold-up to running with LiPo batteries for a reasonable amount of time. I've been using Reedy Plutonium silver-compound brushes, but as I've learned, silver is more abrasive than copper and the result is the Plutonium brushes are wearing-down my commutators faster than I'd like. My commutators start to go out-of-round at the edges of the pads within a few runs, and it's not long after that before they need to be lathed to restore their performance.

Does anyone know where I can get hard-compound brushes that are made from a normal copper/carbon compound, instead of silver? Standup brushes are fine, I'm probably going to convert my laydown motors to use standup brushes in the near future anyway, to reduce the number of different spare brushes I have to keep on-hand.

 

[JatoTheRipper]

Did you check out Team Brood?

Team Brood Racing :: Brushed Motor Parts :: Brushes

An industrial supply house like McMaster-Carr is another place to check, but I'm not sure if they'll have the correct size. https://www.mcmaster.com/#motor-brushes/=17r6qwe

 

[fyrstormer]

Hmm. Team Brood does appear to have several options, but unfortunately they don't specify any information about the brush compounds in their product listings.

 

[EddieO]

Thats because most companies never released much info whats in a brush, let alone any customers really caring.

Silver is similar in hardness to copper...its the other crap in the brush that causes the extra wear.

All of the harder long wearing brushes had silver put in them, because if they were copper, they were simply a dog in the motor...the Plutonium brushes along with the XXX from trinity, the CS, etc....all lasted long as a brush, but they ALL ate comms for lunch, even on 4 cell NIMH...

If the truck is not seeing much water, a long wearing softer brush is what you want to prolong comm life....a 729 or an Enduro would be the choice. Both hold up fine to lipo....brushes are like many things....you can't have the best of both worlds. You have to either choose brush life or comm life....you won't find a brush that does both.

Later EddieO

 

[fyrstormer]

What is the "other crap" put into silver-compound brushes that makes them so much more abrasive than copper brushes? I know that copper is a self-lubricating metal, hence its use to make bronze bushings, but silver apparently isn't; I was under the impression after talking to various motor experts that this was the main reason silver brushes cause so much more wear.

The brushes in disposable motors seem to strike a good balance between brush hardness and comm longevity. That's what I'd like to get in my rebuildable motors. When I look at the surfaces of disposable-motor brushes, they're always dark grey and glossy, which tells me they have a lot of graphite in them. Does anyone make graphite brushes in the standard size used by RC motors? I know Holmes has some for their Puller motors, but those are a non-standard size as far as I can tell.

The motors I want to change the brushes in don't see water very often (or at all, in the case of my touring cars and rally cars), but they do see high amperage, due to the application. I know high amperage contributes to comm wear from arcing, so I'd like to mitigate that as much as possible without switching to brushes that have to be replaced every time I turn around.

 

[kongluc]

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[JohnRobHolmes]

Silver is more abrasive to copper than copper is. Our silver brushes are the same density and graphite content as the standard soft copper brush, but with some copper replaced by silver. If silver content is more than 1/20 of copper content, the hardness starts to drastically change. As Eddie stated, it will always be a trade off to tweak compound or hardness. Brush life or comm life, can't have both with a high conductivity brush.


The origional Puller brushes wore so long because of a teeny tiny doping of molybdenum. It affects conductivity too, makes them less conductive which also suppresses arcing. The larger size offset conductivity losses.

 

[EddieO]

I will be honest, I am not a chemical engineer.....my info comes from the guys at Keystone, who made many of the brushes we saw in rc racing. Silver needs different bonding agents from my understanding. As a metal its typically softer than copper. Abrasiveness is basically measured in the hardness of the material. As John stated though, rubbing copper on copper is less abrasive than silver on copper, which is actually the same thing the keystone guy said to me when I was looking into getting a brush made. The Keystone guy explained this as a reaction between the two metals along with increased conductivity that accelerated the comm wear.

As to the other crap, your guess is as good as mine....They would put all types of different stuff in them in search of the holy grail brush. Besides the standard copper, graphite, silver, etc...they would use materials like John mentioned to dope the brush, along with bonding agents depending on the materials used to make up the brush. Brush compounds were closely guarded secrets....on top of that they varied from batch to batch.


Copper is not self lubricating on its own, some of its alloys, such as Bronze are....I would guess Silver isn't used for bearings due to cost along with it not alloying with other materials as well like copper does for brass or bronze.

You won't find a standup or laydown brush like what comes in the mabuchi or johnson style motors very easy. Maybe some old stock from the 90s or older. Companies stopped producing them long ago, simply because nobody wanted them. They made them when I was a kid. I ended up with a pair once, put them in my new motor at a big race, car was slower than can be. Installed new brushes after, was fast again. You could dry to source some graphite brushes and cut them down....be prepared for a mess though

Later EddieO

 

[JohnRobHolmes]

Certainly, part of (or most of) the increased comm wear of silver brushes is increased conductivity allowing higher current inrush. It also prevents the comm from developing the same "patina" that graphite or copper/graphite promotes. The interstitial patina is a critical part of a long service life, as it has higher conductivity and lower friction than copper oxide that would otherwise form. Water wears brushes by removing the interstitial layer, and the brush wears more while trying to redeposit it. This is also why pure metal brushes use a non conductive lubricant. It serves as an interstitial layer but more importantly seals surfaces to prevent abrasive copper or silver oxide from forming.

Lots of fantastic scientific information on NASAs jet propulsion lab website, buried within white papers and technical documentation. They have gone to great lengths to understand commutating surfaces, and it seems that a jewel of information always comes from seemingly unrelated situations.

 

[fyrstormer]

I didn't realize only 5% silver was necessary to significantly increase the hardness of the brush. This changes my opinion about "silver-containing" brushes that are obviously copper-colored. So for my application, where I have low-turn high-wattage motors that don't get wet often (or ever), and I'm willing to trade *some* increased comm wear for slower brush wear, would you recommend something like a 5% silver brush instead of a plain copper brush? If so, can you recommend one? I only see soft copper brushes and full-silver(?) brushes on the Holmes website, Team Associated seems to be sold out of most of their brushes, and I can't tell if Team Trinity even makes brushes anymore. It would be nice if the brushes had no eyelets on the ends, because I prefer to solder the shunts directly to the tabs, and cutting off the ends of the shunts to remove the eyelets makes it a little harder for the shunts to reach the tabs.

 

[EeePee]

Stormer always had a stash.

https://shop.stormerhobbies.com/cat...5&cat=806&show=10&page=1&minprice=&maxprice=3

https://shop.stormerhobbies.com/cat...&cat=806&minprice=3&maxprice=9&show=10&page=1

 

[JohnRobHolmes]

Abrasiveness would be more accurate than hardness to describe higher silver content I suppose. If I recall correctly, my silver brush is 5% silver. I'll have to find my notes, but it is a low amount. They look more silver because of the process. Size of the powder and order of mixing influences color. I sent off many brushes to a mass spectrometry lab and found that color doesn't always reveal the full story.

I would choose Putnam brushes for what you want, any type. I have a stash that I don't really want to sell, maybe there are some left online somewhere?

 

[fyrstormer]

Stormer always had a stash.

https://shop.stormerhobbies.com/cat...5&cat=806&show=10&page=1&minprice=&maxprice=3

https://shop.stormerhobbies.com/cat...&cat=806&minprice=3&maxprice=9&show=10&page=1

Dear god there are a lot of different brushes with modified faces. Simple serrated brushes are fine, I don't need holes or slots drilled into them.

Abrasiveness would be more accurate than hardness to describe higher silver content I suppose.

So silver content *only* improves conductivity, and has no meaningful effect on brush longevity? Hmm.

If I recall correctly, my silver brush is 5% silver. I'll have to find my notes, but it is a low amount. They look more silver because of the process. Size of the powder and order of mixing influences color. I sent off many brushes to a mass spectrometry lab and found that color doesn't always reveal the full story.

I love how seriously you take your work.

I would choose Putnam brushes for what you want, any type. I have a stash that I don't really want to sell, maybe there are some left online somewhere?

It looks like Team Brood has some Putnam laydown brushes, but I can't find Putnam standup brushes anywhere. *sigh* Time to add another saved-search to my eBay account.

 

[EddieO]

The putnam standups were just a relabeled brush that other companies sold. I did not stock them, as they were junk in the race motors. His laydowns were very abrasive on the comm, especially the green, blue not as much...red was pretty tame, they were fast though. The last few batches of putnam laydowns were not even the same brushes, he could not get more from them, so he bought other company brushes and dipped the shunts in dye...I threw away the last batch I got from him, as they were clearly not the same brush....

Stormer appears to have some good deals on the Orion brushes....Try the Enduro units, even the sprints are fairly tame...they sold them with lots of different faces (hole, cut, slot, checkered).

Later EddieO

 

[fyrstormer]

Thanks. I'm using Enduro brushes in an Orion Revolution motor and they've been working pretty well; I didn't realize they were available in a normal rectangular shape too. I'll have to take another look.

 

[fyrstormer]

After trying to hunt down reliable suppliers for various different brushes, I decided to try some 20% silver brushes from Team Trinity. Hopefully they will be able to strike a balance between reducing comm wear without accelerating brush wear too much. I ran-in the brushes with the throttle trim turned up for a couple minutes, then took the car outside for a couple top-speed runs. My multimeter says the 20% silver brushes rate at 0.2 ohms from the face of the brush to the end of the shunt, whereas the Reedy Plutonium brushes rate at 0.05 ohms, but that slightly increased resistance wasn't enough to slow down the car I installed them in for initial testing. After 3 top-speed runs, the serrations haven't worn-down completely, so hopefully the brushes will have a decent lifespan. We'll see how my Traxxas Slash responds tomorrow; that truck has a Holmes TorqueMaster Pro 550 11t motor in it, and it's a brush-devouring monster; slightly higher resistance might actually be a good thing in that respect.

 

[EddieO]

If they are the XXX Brushes, they will last a while like the Reedy Plutonium....but expect extra comm wear. We didn't use them a ton in the racing days, because of price and they ate the comm pretty bad in some cases....lots of fade at the end of the run from them in 19t and stock motors, though we did use them in the ultrabird 19t at snowbirds with adjustable timing at 50 degrees....They worked ok in mod if you had everything right...(timing, spring tension, etc)..

Later EddieO

 

[fyrstormer]

These aren't XXX brushes, though I've used those in other motors in the past. XXX's are 100% silver or close to it; these have the product code 4403NT and have a noticeable brownish color, though not as obvious as a 100% copper brush.

 

[EddieO]

Ah, 4403...used those occasionally back in the racing days, they were kinda the in between a 4380 and 4383 in performance.

The XXX brushes don't have 100% silver content....I think Jim told me it was still less than 50% or so...there is another element in it that magnified the silver look to them that they added on purpose for the look. Someone had them analyzed way back and the CS Brush had the most...CP INfinity had more than the XXX, so did the Reedy V1, they changed in the second batch, so not sure what it was then.

Later EddieO

 

[fyrstormer]

I've installed the 4403s in two motors thus far, one high-speed and lightly-loaded and the other high-speed and heavily-loaded, and both motors run at the same speed they used to. So that's good. I haven't installed them in any low-speed motors yet, but that's coming next. The lifespan of the brushes and the wear on the commutator can only be determined through long-term use, though.

I'm not racing, so I don't demand super-high performance, I just want my brushed motors to run a long time between teardowns and without becoming dog-slow. Yes, yes, I know, volt-up and gear-down, but I'm stubborn and I'd rather address it through mechanical changes instead of electrical changes.