# Brushless Magnet Life



## pmsimkins (Nov 4, 2004)

I run brushless 4 cell oval. The motors get quite warm, right to the edge of thermal shutdown to be fast. What are people's opinions regarding the life of the magnet given this heat cycling? I have run mine all indoor season and haven't seen a power let down of any kind, at least that I can tell. Eventually I assume I'll have to replace the arm as the magnet will sooner or later lose some strength. Does someone know is the magnet a SmCo or is it the usual ferrite?


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## starluckrc (Feb 18, 2005)

Depends on the manufacturer. Ferrite isn't common in brushless. Most of the good motors use 110 degree C magnets, so they can take pretty high heat before demagging the rotor.


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## kevinm (Jan 16, 2002)

The Novak motors (and probably all the other brands) use neodymium. According to one magnet supplier's web site, neodymium is the strongest magnetic material, with an operating temperature of 176° to 356°F, depending on the "grade" used. Samarium-cobalt has a higher temp. limit, but the element is more rare and therefore expensive.


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## pmsimkins (Nov 4, 2004)

I checked the Novak site. They do use a Neo magnet, quite surprising. I design magnet proximity sensors for a living. We never use Neo for the application with the kind of heat a BL motor sees. The highest grade, supposedly, is serviceable to 150 C but from my experiece it is problematic. Kevin you are right that at room temp Neo can be stronger, but at 100 C it loses 9-13% of it strength while SmCo is only going to lose 1.5% to 3% of its strength so that somewhat evens out. SmCo must be too costly for them, that is the only reason not to use it for this application. Well now that I know they use Neo I am happy to see they have come out with a replacement rotor, because I'll be replacing mine on a regular basis.


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## DynoMoHum (Sep 25, 2001)

pmsimkins... maybe you've found a new market... for thrid party brushless armatures made of SmCo.


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## kevinm (Jan 16, 2002)

All the info I posted came from a magnet makers website. Reedy's upcoming brushless motor is named the "Neo One". Guess what they are using.....


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## hankster (Jan 1, 1998)

Since there is a cost limit on ROAR legal motors my guess is they have to use Neo magnets to hold costs below that limit.


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## patcollins (Sep 29, 2001)

I remember reading one time that SmCo mags really didnt work that well with only 6 cells but at higher voltages they really came to life.


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## pmsimkins (Nov 4, 2004)

There used to be brushed drag motors made with SmCo magnets. With the regular brushed motors there is a limit to how strong you want the magnets relative to how strong the electro magnet (armature) is, that is why the SmCo brushed motors may have worked better for high voltage drag cars. With the brushless that wouldn't really apply since they are already using Neo which is equal to or stronger than SmCo.

I didn't consider the price limit thing. I wasn't sure how or if that applied to the BL motors. I suppose it must though.

One other word of caution for people when dealing with these motors. If you take it apart to oil the bushings or out of curiosity, make sure you don't scratch that coating on the rotor. Neo corrodes very very quickly, which is why you'll often see those magnets coated with something.


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## pmsimkins (Nov 4, 2004)

I'll probably replace my rotor before the outdoor season starts. At that time I'll take the old and new rotors to work and test them a bit on a gauss meter to try to see if there has been significant weakening. Should be interesting although it's tricky getting consistent results with a gauss probe. We've got a capacitive discharge magnetizer that can do Neo's but I don't think my boss would appreciate me spending a week tring to figure out how to zap the rotor.


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## DynoMoHum (Sep 25, 2001)

When I looked at the arms in the Novak motors, I couldn't see any identifying marks... and well it would seem if somone were to make other arms of other material, but looked like the originals... there would be almost no way to tech... That is unless any rules that might come along require identifying marks, etc...


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## Echeconnee (Nov 14, 1998)

I have one of the original Novak 5800 systems and have run it 6 cell in mod mode in a truck and 4 cell in a pan car in the stock mode. I also have a new 5800 system, I can't tell any difference between them. And teching the rotor would be a breeze, the smco and neo magnets are different enough in weight that a cheater would be easy to expose. I can't remember why I know that but I am pretty sure the neo mags are considerably lighter than cobalt. There will be a hundred different ways to cheat with the new technology but a track owner who is a quick study will know them all in no time. I know I have been on the phone with Novak and LRP a lot asking just those sort of questions.


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## TeamGoodwrench (Oct 14, 2002)

pmsimkins said:


> I checked the Novak site. They do use a Neo magnet, quite surprising. I design magnet proximity sensors for a living. We never use Neo for the application with the kind of heat a BL motor sees. The highest grade, supposedly, is serviceable to 150 C but from my experiece it is problematic. Kevin you are right that at room temp Neo can be stronger, but at 100 C it loses 9-13% of it strength while SmCo is only going to lose 1.5% to 3% of its strength so that somewhat evens out. SmCo must be too costly for them, that is the only reason not to use it for this application. Well now that I know they use Neo I am happy to see they have come out with a replacement rotor, because I'll be replacing mine on a regular basis.


 
So how often is "on a regular basis" ??

I hope we haven't gone from replacing brushes to replacing rotors on the same schedule


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## pmsimkins (Nov 4, 2004)

Jeff,

I was thinking "regular" as in once a season or something or maybe before a big race. I think I mentioned in my first post I have not noticed any deteriation of mine in on track performance, but that is awfully hard to guage. Anyway I have no plans to replace mine even on a monthly basis. 

You'll actually have to come out and race with us before you have to worry about wearing yours out!!!


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## TeamGoodwrench (Oct 14, 2002)

I ran brushless this past weekend in Marshalltown Iowa at their concrete oval.

It was a blast. I was TQ on Sunday. Phil B., Scott Murphy, and the crew were there and it was a lot of fun.

I'm planning on making one of the JW races under the lights this year.

Thx.

Jeff.


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## pmsimkins (Nov 4, 2004)

Cool Jeff. Good run. Danny B. mentioned in the Tri-Clone thread that there was quite the BL turnout. Will they be running any special races later this summer?


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## TeamGoodwrench (Oct 14, 2002)

I'm not sure -- I know there aren't any "special" races at Marshalltown. Not sure about Storm Steel. You can check on their website at: http://www.iroaronline.org/


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## vwal (Nov 11, 2001)

Every race at mtown is special.....


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## crisis641 (May 27, 2002)

Generally the Fair Race in July is as close as we get to a special race. Hope to see you make it down Pat


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## TeamGoodwrench (Oct 14, 2002)

I really miss the "old days".. back when they had the "Oktemberfest 400" race. I've got the A-Main plaque from 1992 by my computer here. <sigh>


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## pmsimkins (Nov 4, 2004)

As promised I had a chance to test an old versus a new rotor. The old rotor probably had about 30 race days on it. The new one had 1 race day. The old rotor showed about 2.5% drop in strength (flux density). Not too much at all. I think most of the heat the motors generate is dissipated through the can since the windings are on the outside. The rotor probably never gets too hot.


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## patcollins (Sep 29, 2001)

Was that an actual drop or was the 2.5% difference there from the begining? 

I have ran mine about 50 battery packs or so and see no appreciable loss in power or torque.


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## pmsimkins (Nov 4, 2004)

patcollins said:


> Was that an actual drop or was the 2.5% difference there from the begining?
> 
> I have ran mine about 50 battery packs or so and see no appreciable loss in power or torque.


I don't know. That was kind of my point. The drop is insignificant enough to easily just be variation in the magnets. I would need a much larger sample size to tell for sure. Even if it truly is a decrease in performance it is small enough to be inconsequential. That is definately a good thing.


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## kevinm (Jan 16, 2002)

I also saw a small loss of magnet strength in mine compared to a new, unused one. But when I tested the entire system on the dyno, it actually showed slightly MORE power than when it was new.


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## pmsimkins (Nov 4, 2004)

I would not use a brand new one (never been run) as a comparison. Since it has not been in the magnetic circuit it will certainly be stronger. As soon as the motor is run just once the new rotor loses some strength. That is why I used one with 1 race day and compared to one with 30 race days.

The reason why the weaker magnet motor may have read stronger on the dyno is that a weaker magnet will allow for higher rpms under a low load condition. This may show as an increase in power.


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## patcollins (Sep 29, 2001)

There is such a thing as having a magnet too strong for the amount of voltage that the motor will run on. 

I think this may be the case in 4 cell, many 4 cell racers claim that the Novak motors are much closer to a stock motor on 4 cells than it is on 6. 

Big Jim always said rare earth magnets didn't do well in 6 cell applications, but this was with brushed motors.


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## vwal (Nov 11, 2001)

That is pretty cool about the rotors, I figured there wouldn't be too much difference but it is always good to have numbers. I am super happy with BL. I am looking forward to the new motors coming out to see what will be good for indoor modified racing!!


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## kevinm (Jan 16, 2002)

pmsimkins said:


> The reason why the weaker magnet motor may have read stronger on the dyno is that a weaker magnet will allow for higher rpms under a low load condition. This may show as an increase in power.


It wasn't what I'd call a low load. It had 3-4 more watts at 35, 40 & 45 amps. Although I have seen dyno readings vary slightly from day to day, it's still good to know that the performance doesn't change significantly after hard use. Now if the battery companies can come up with Nimh cells that will last a year or two.....


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## Ted C (Dec 4, 2001)

Hi
What type of dyno did you test with? I tried once with a fantom and could not get it to work. Not sure if I did it wrong or if you guys have a different dyno or a better way. Thanks Ted C.


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## kevinm (Jan 16, 2002)

I used a Competition Electronics Turbo Dyno. It uses a slave motor to perform basically "static" tests at several steps of amp load, rather than the flywheel style of the Fantom. It ramps the current up at the start, instead of just slamming the 5 volts to it.


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## RPM (Dec 20, 2004)

Well a new rotor will only cost about $16.00 for the Novak 5800 system.

That's alot cheaper then brushes springs, com cutter, etc. 

F.Y.I.
I heard that Castle Creations is comming out with a new 10th scale brushless system in a few weeks release date. :dude:


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## starluckrc (Feb 18, 2005)

Castle is still a few weeks off. I will have them in stock as soon as they are available and will dump some beta feedback on the forum as allowed.


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