Questions on heat

[Dafni]

Hi folks, I got another question to discuss here.
Where exactly is the heat in BL motors generated?? Is it the winings or the actual magnet that creates the heat?

I know our Neodymium magnets will loose the perma-magnetism above 120°C, but will gradually fade above 90 or 100°C.

Now, on my 9L I sometimes get readings up to 90°C on the can. Ususally it's hotter towards the rear end, where the wires stick out. I know this is already in the critical area, so I'm looking forward to Mikes heatsink.

Suggestions and thoughts are welcome!
Thanks alot

DAF

[Dagger Thrasher]

Good question...I'm afraid I can't help you, but I'd also like to know some info on this please. When I do eventually get my BL setup (i'm determined it will happen someday, lol!) it would be really handy to know more about this sort of stuff...and you guys really know what you're talking about. Thanks.:)

[Serum]

The reason for the heat building up is the efficiency of the motor. the losses of the motor are translated into noise and heat.

The magnetic field, that circles around the magnet is not able to translate into power for the magnet for full 100% (that is also depending on the quality of the magnets and the space between the magnets and the electro magnetical field)

The copper wires that make the magnetic field are not able to produce 100% of magnetic power out of the electric power it gets

These things toghether, and the mechanical losses, produce the heat.

The motorcharts, that are made by BK (Lehner) show the most ideal input/output ratio (efficiency) but Feigao doesn't make these kind of charts..

[Dafni]

I see. Thanks for the info.
Too bad there is no such chart for the Feigaos.

Another question: My Revo has pretty much a Maxx setup (EMaxx tranny, same diff-reduction, Maxx wheels) and I have it geared at 16/66. Now the motor (9L) get's above 70°C pretty quick, and most times ends up at around 90°C (190F, I think). Should I be worried?
The drivetrain is smooth and free of binding. I run 14 matched GP 3300 cells. The controller and the batts stay rather cool. I don't think I geared it to high, what's your opinion?
The track I drive at has alot of up and downs, alot of accelerating in upwards slopes. And I hardly use the brakes at all.
Ah, yes, this track is so tight, most times I spend the whole packs only in first gear. (that's the reason I think I should be on the save side with the gearing, and why I'm surprised at those high temps)

Please post your suggestions or comments. As soon as I get my next order, I will have Mikes heatsink. But I assume this will only have a small impact on the actual temp at the magnet.

Thanks you for your help
DAF

[HotnCold]

I have had the same problems with the temps creeping as well. I actually run a 12V fan on my motor to help keep the temps reasonable. The only drawback to that is there is no way to mount a fan and make it look halfway decent. No matter which way its mounted it always looks getto. IMO...

[Dafni]

I agree, HotnCold.

I will also cut some "inlets" in the windshield of my body, and make a smart design so the air gets directed at the motor and controller. This should have a similar effect as a fan, with the obvious dis/advantages.
On top of the ugliness (fan) comes the lack of space in my case. I like to keep the body as low as possible. (but this also places the motor and controller nicely behind the windshield)

I hope RC Monster Mike posts something about my gearing question.

[Serum]

You could try a 72 tooth spur, and measure the temps again.

The 16/66 should work fine, other users use that gearing too..

The heatsink will lower the complete temp of the motor, not only the outside, but the rotor too.

[Toon]

These are the temps of my 9L/9918 setup after its first full run (as seen here) :

After nearly 13 minutes of hard running (geared 17/66 with UE diffs, on 14 GP3700 cells), the controller was at 140*F (60*C), the motor heatsink was 120*F (50*C), the motors rear end plate was 140*F (60*C), and the bit of purple can thats visible was at 175*F (80*C). Could the higher temp reading be due to the different colors/reflectiveness of the various parts of the motor?

When I first read your post Dafni, I got very worried seeing you say your motor was getting to 90*, making me think that mine was getting way too hot. Then I realised it said 90*C, not 90*F! :L:

[Serum]

You are using another gearing ratio than Dafni, he is using stock diffs and you are using the UE's.

[Dafni]

Toon, your temps are very similar to what i get. Altough I don't have the heatsink yet.
Thanks for giving both values. Yes, C to F conversions are a pain, and confusing, too. We had this topic here before :L:

Thanks for sharing your experiences. Keep an eye on the temps.

Serum, I'm looking forward to the heatsink. I wonder how big the effect will be. Yes, the gearing should be fine. Especially since I drive in first gear for most of the time (which is a 1:30 overall reduction, I think)

[RC-Monster Mike]

Daf,
Your gearing is fine. You may even gear up if you only run in first gear or gear down and only run in second gear. You may even get cooler temps if you run a slightly lower gear in second only. Your motor may have too little resistance in 1st gear with that gearing. If you went to a 72 spur, you would only loose a couple mph off the top end, but you could put down faster laps without shifting. Dropping to a 15 pinion would be almost the same thing.

[Dafni]

Thanks for this helpfull info, Mike.
What 72t spur would you suggest, then?

This thing about my motor having too little resistance, you mean mechanical or elecrtical? I guess mechanical, right? So you think the motor revs up too quick, like I'm in the upper rpm range more often??

I would like to try a bigger spur, so if you have one lying around, you know where you can put it;)



Edit: Wooh, my sig works:L: LMK if you think it's too big, I got inspired by HotnCold.

[Serum]

Impresive sig..

only thing missing is the RC-monster heatsink.. ;)


The thing Mike is talking about is that motors are a ineffecient when they are not loaded (mechanical) they will get hot when they run unloaded. (by the electrical/electromagnetical losses on a no-load.. (it is running high rpm's)

My Mamba on my mini-t, gets hot within 1-2 secconds on a no load on a 3S lipo. When i drive it, the 8K stays cooler..

[Dafni]

Thanks :)

The heatsink will be on its way soon!

Yes, I figured something like this. So, wouldn't a bigger spur only make it worse? Or would you suggest getting a bigger spur and driving in 2nd more often?
Would this be another possibility: Getting a bigger pinion and only driving in 2nd for speed runs??

[Serum]

Just try a small step at the time, and measure the temp.

You have got a pinion that is 2 teeth larger? That would't hurt.