Questions on heat
 

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

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.:)

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..

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

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...

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.

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.

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:

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

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)

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.

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.

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..

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??

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.

As you know, I currently run a 16/66 setup.

I have an 18 and a 20t pinion here, as well as an 14t. They have to be 5mm, as cou can imagine, that's why it's hard for me to get them. The 18 and 20 are good one, but the 14t looks a bit sketchy.

I don't have any other spurs as yet.

So would you suggest going 18/66? Kinda strange, but I see the point. Actually I would have thought a smaller pinion would give me lower temps. But I perfectly understand that my motor may have been undergeared.

What would be your suggestion? Do you know of any people running this gearing in a simillar setup?

Some food foryour brain;

A friend of mine geared his 6.4 kg heavy savage with a 10L like this;

(he uses 13,14 or 15 cells)

14/49 or 16/49 for high speed runs
14/49 on a Savage results in 25.61:1 in 1st and 17.79:1 in 2nd
16/49 on a Savage results in 22.41:1 in 1st and 15.57:1 in 2nd

His temps (measured on the 5 mm thick motorshaft) Highest temp he measured was 78 degrees (schulze speedo on 19khz) and on 9khz his highest temp measured is 68 (after two full runs) (outside temp was about 15 degrees)

I don't know what the timing is on the 9918 controller...

He told me, he heard that the motor may become 110 degrees on the shaft, i personally think that is high, considering that the magnet looses force when it gets hot, and it will get hotter and hotter, because it loses force (lower efficiency will result in higher temp)

Thanks for the input, Serum.

The 9918 has 15° timing, but this can be changed. Also, you can set it to Autotiming (whatever that means).

I think 110°C is a bit high. The Neodymium alloy undergoes a phase-transition at around 120°C, which may lead to instant loss of the magnetism. But I think this is a rather smooth transition, where the magnetism just fades over time. But theoretically you could kill the magnetsim by heat within a few seconds. I don't know the actual temp, though.
However, on our motors, I would say the lower the better, and I trust the guys who say everything below 80° is pretty save.

I will try the 18t and see what temps I get. I will also add a oneway to the fron end. This should reduce some brake stress on the system. Let's see. I just want a setup where I can run pack after pack without worries.

The 18 or the 20 in first gear should be plenty fast for the track you run on, and you could keep it in first gear. It wouldn't hurt to put a fan on the motor, either. It looks like you can't really get too fast on your track, so the motor gets almost no airflow to keep it cool. Let us know how the 18 pinion runs.

Today I had another test run, still on 16/66. But this time I kept it in 2nd.
Did a few laps on my small tack, some speed runs on asphalt and some bashing in the wood.
And indeed, (surprisingly for me) the temps stayed a fair bit lower.
Unfortunately I left the IR temp thingy ar home:o But I got quite good at the finger test:)

So I reckon this would be a sign for undergearing, then? At least in first gear.

I also finally had a close look at the final gear ratios. Please correct me when I'm wrong.

16/66 > 1:32.5 in 1st and 1:20.2 for 2nd
18/66 > 1:28.9 / 1:17.9

16/72 1:35.5 / 1:22.0
18/72 1:31.5 / 1:19.6

Okay, so assuming 1:32 is too low, what would be ideal?
You know my setup, but feel free to ask if yo want to know something specific.
I just weighted the Revoxx again, full RTR, and it's almost exactly 4.5kg (9 pounds)

What would you suggest for a safe gearing? Is the 18/66 with its 1:17.9 already too high for off-road bashing?

It would be great if I could use the 1rd gear without worries, but it should also be safe to stay in 2nd for a whole pack.
Am I asking too much, or do you think this should be possible.
I take it most of you guys drive your BL G-Maxxes mainly in one gear, right?

You can only descide for yourself what the ideal gearing is.

If i was put in your place, i would just try it and ask a person who had a lathe, to drill out a 3.2 bore to 5mm on different pinions. (or you could order a few from Mike) Just measure the temps on the speedo, motor and batteries.

Just measure the temps, that is a very important value. Also look at the temp on your batteries, because their lifetime will be shortened when constantly pushed to their max.

Do you think you need both gears (1st and 2nd?) i personally really fancy the G-maxx 1 speed conversion. It would shave of a little weight as well (shiftingservo, gears, one piece of the gearbox)

4.5kg RTR is very light! (9.9 lbs, for the non european.. ;) )

Hmm, I really like this ability to have 2 gears. No shift-on-the-fly, though. I just like to bash on my small track in first, without having to change pinions for something bigger.

I begin to believe that the difference in the 2 speeds gearing ratio is already to wide for being save in both gears over a long time. Well, at least for my setup.

Of course I have to find out for myself. I just never thought there might be something like under-gearing. (hotter in 1st than 2nd)
Apparently 1:32 is undergearing on my Truck (maybe I should add a bit weight:L: )

However, I would still like to ask the same question: Would 1:18 be overgeared?

Yes, I plan to get the proper pinions from RC-Monster.
My batts stay surprisingly cool, barely hand warm. And the controller is also rather cool. It just get's warm when I drive in second.

I had a full run in second only: ESC 60°C, 9L 75°C

Yes, the Revoxx IS very light, even with shifting servo and all. Everytime I have to pick it up without batts, or even without wheels, I'm like: whoa, babe's a lightweight. :) But I might add some stuff to make it better, though, and heavier too, for better of worse.

Double post, I know:o But I have a (more sensible) question this time.

Look, heat is about the only indicator we have on how our systems is actually doing. Apparently you can tell by the different temps if a system is struggling or somethings wrong.

For example, a hot motor can either be due to under- or overgearing. Agree?

Hot batteries are a sign of a too high current draw, I think.

And a hot controller means ....uhm, maybe someone can help me there.

My experience on my 9L shows that it's obviously undergeared on 16/88. When I stay in first gear, the motor gets hot, but the controller stays exceptionally cool, and vice versa in second gear. Motor stays a bit cooler, but the controller is like 80°C.
The batts always stay cool, like 30-35°C.

I have heard from other guys that their batts get hot. I only ever had hot batts on my brushed Maxx.

What do you think on this. Some input would be great. I like to understand things, and it drives me nuts when something won't make sense.

I also had a close look at the literature on NdFeB magnets, and found out about all the different grades and the maximum temperature they can handle. It's an interesting matter, and I look forward to test some other combos.

Thanks for reading
DAF

The higher the quality of the batteries (read; lower internal ressistance) the colder they stay.

The controller on 80 degrees, why don't you use a fan?

It depends on how the controller is developed/designed.

Let's say a transistor/fet can deliver 25A on 20 degrees, when the temperature rises till 70 degrees, that same fet/transistor can only deliver a 5A So it depends on the amount of fets/transistors that the controller has got in it, how much A it can handle when it is 80 degree, but it is always less than when the contoller is cool.. A fan might be handy for you right now.

Hmm, there seems to be no getting around a fan for me, then.
I have a fan on my brushed ESC, and also have a few fans lying around, those 12V computer fans, 4cm and 8cm, I think.
I'm just hesitant on the Revo bacause I don't really have space and I like the clean look it has now.
But you're right, I'll have a look at this.

80°C on the ESC is the extreme case, after 2 sets of packs back to back.

Wait, just got an idea: How about taking one of those 4mm fans and put it under the shrink wrap? This would look clean as well.
And then I would power it with the 18V from my packs.
Think this would work?? Could I just wire it to the input leads of my controller (which is a warrior 9918, btw)??

Just make sure the air blowing from the fan has somewhere to go.

Sure! Have to think about a nice flow.

I already found some 25 x 25mm or 30 x 30mm fans at an electronic supplier.

Is it possible to wire them directly to the input leads of the controller? Or will this have an impact on the performance??

I think I will mod my warrior. If it can be done clean I'll give it a try.
Expect pics when I'm done. I'm thinking of two small fans directly on the heatsink, covered with shrink. With some proper inlets as well as outlets, f'course.

It would be nice to get a real clean way to mount a fan to the speed controller. Its hard to make a fan look clean and also function correctly.

You probably have seen this, this is how i mounted the fan on the 9918.. (2X M3 screws)

http://www.serum.demon.nl/BL%20lightning%20PRO/21.JPG

http://www.serum.demon.nl/BL%20lightning%20PRO/18.JPG

and that's the frame i use for that 9918 It would gain a little bit of weight, but that a small sacrifice to make for a descent speedoholder®

Looks good, I like this frame thing. Thanks for the pics.
Is this a 4 x 4cm van??

How about the wireing? Can I wire it directly to the input leads of the esc?

I will get two smaller vans, have to take the exact measurement tonight, and then shrink them on. Let's see how it works.

I thought about wireing two 12V fans in series and feed it with the 14 cells. What do you think?

I would use a 7812 voltage regulator (to220 housing). and use the two fans parralel.

The fan i used is a 30X30mm fan.

It was a perfect fit though. make it so, it blows over the heatsink, not sucking.. pressure cools better than vacuum.

to220 housing? Can you please explain this?

Can you post a pic of this regulator?

How about wireing in paralel, using the 14 cells, and add a suitable resistor??

Eitehr way, you solder it to the input wires of the ESC, right?

I have a fan on my brush Maxx, and I use a separate 9V dry cell:o

Will get back to you on this tomorrow.

Thanks so far guys, especially you, Serum. Nice talking to you.

DAF

That's okay Dafni!

TO220 is a type of housing for transistors and fetts.

Look here for detailed instructions.

You can use the power that comes from the 14 cells. So it is the best, to connect it to the side of the esc. (when you plug the batteries in, it directly powers the fans as well)

Great! Watch out for my modded Warrior. I can see the picture clear in my mind. Should turn out nice and clean. Let's see.

I had a close look at it yesterday, and I think it's do-able for me. I will order the needed stuff today.

Okay, here's my fan mod.
I did one with regulator, and one with just a resistor. Both work well, but for reasons of "clean-ness" I'll stay with the resistor.

http://img.photobucket.com/albums/v3...ee/9918fan.jpg

The airflow is not hindered. The outflow goes thru the end of the heatshrink, where the cables and caps are, and thru some holes I made.

Please tell me what you think.

That background is quite impressive.. ;)

It is clean, no doubt. It's cleaner than with the regulator. I see what you mean.

did you glued them on?

The fans are held in place by this 3 screws you can see on the upper edge. Fortunately 3mm screws fit nicely between the fins of the heatsink, they kinda cut their own thread.
A nice feat, I think. No glue or messy stuff involfed, and you can remove it (almost) without a trace.

Ja, the Periodic Table of the Elements has something to it:D

On the subject of heat, what would be too hot? I ran a 6 cell pack geared 21/84 and the motor temp after the pack was drained was 151 F. I dropped to a 19 tooth pinion and the motor temp was 115 F. What temps max should I be trying to stay under in my Stampede with the Feigao 8s?

Neither of those temps are too hot. Keep things below 180 or so and you won't have any trouble. 115F is cool! 151F is no problem at all.

Mike, I usually end up with my 9L at 190°F, geared 16/72 :eek:

Another thing, much more worrying: My 9918 with the dual fans stays nice and cool on the upper side, but I noticed it gets hot on the underside. It is mounted on some velcro (plus zip ties, of course) and sits on a sheet of alu.
Yesterday, it was a really hot day, it thermaled!! Temps on the heatsink barely above 100°F, but it was hot underneath.

What can I do there? Any ideas?