How to kill a motor?

[DaveG28]

Had a very nearly new Novak 5.5L conk out on me today, just stopped working at all!? Is it possible to kill them from overheating, you could smell the burning at the end of each race from the motor up to the round where it went pop, so wondered if I've killed it that way, or if it might be worth me sending it off to Novak or someone as its so new?

Alternatively, what else might have gone wrong!?

[jono83]

I think you answered that yourself

[Dagger Thrasher]

Yep, that sounds like you've fried the motor I'm afraid. It's easy to kill a brushless motor from overheating/overgearing. The rotor of any brushless motor has a maximum temperature that it can tolerate before it gets demagnetised...in the case of Novak motors, this is around the 175F mark. When a rotor begins to "de-mag", the motor has to pull more current to make up for the weaker magnetic field, so the motor gets even hotter, even more current is pulled and the rotor de-mags even more until the motor's dead. You're lucky you didn't fry your ESC, too; the current draw from a demagnified motor can be massive, and can kill a speedo very quickly before you notice.

Running a motor over its safe temp can also burn the windings, which is probably the burning smell you describe. Sorry... I don't think Novak are going to help you here. When you get a new motor it's always a good idea to frequently check the motor's temp while you set up its gearing to avoid this happening; ideally, you don't want the motor to be running any hotter than 150F.

[DaveG28]

No worries, my bad then, although I'll replace with a different motor type, unfortunately it was on pretty much the best gearing I could get with the available spur/pinion combinations on the car, the next downwards gearing step is a big one which left it a bit too punchy/too slow top end!

Good lesson learned though, I'd always thought the ESC would thermal before killing the motor, I'll take more care from now on!!

[ianjoyner]

Were you using a GTB? They are supposed to thermal if the motor or ESC gets too hot. I'm not sure if other controllers use the temperature sensor in the motor though.

Sounds like you fried the windings, definitely worth measuing the temp when exploring gearing options. Even without the thermometer though I'm guessing if you can smell burning that's too hot .

[Dagger Thrasher]

That's true, if it was a GTB then they're meant to shut down when the motor overheats...but that isn't always reliable. What car were you running it in, and what was your gearing? You shouldn't have a problem finding a ratio that allows the system to run cool, so perhaps there was some binding in the drivetrain you'd missed?

Thinking about it, it might be worth hooking up another motor, if you have one, to your ESC just to be sure that it's still alive and well.

A temp gun is invaluable when it comes to gearing BL motors.

[josh_smaxx]

The blue wire in the hall sensor lead is the motor temp sensor BTW

[super__dan]

I agree with some of what's said here, a Novak motor or ESC is designed to shut down to prevent over heating with a cutoff that will kick in between 190 and 200 deg f. I have only on one occasion (running a 4.5 in too long grass) had it shut down, but following it cooling down both ESC and motor were/are fine. I'm not suggesting you routinely take your motor and speedo to the thermal cut but if you've done it occasionally I wouldn't lose any sleep.

Sintered rotors are much more resilient to heat, being an L motor it defo does have a sintered rotor. I guess this offers no help as to why it's gone though, you've have to send it in for inspection to find that out.

I do agree a temp gun is very handy and that generally 150degf is a sensible limit, though if necesary (a national say) I'd take it toward 170 again without losing too much sleep.

[Chrislong]

What I would be concerned about is that it does get hot - why? I am running a pretty quick motor in my 4wd, and haven't cut any of the vents out, and it only comes off at a normal hotness... 100 - 110 F .. even Vernon is running his Cat SX with no holes cut in a heavy Nimh car, and he has fried nothing recently (suprisingly).

Which 4wd are you running to have such limitations in gear ratio's? Im finding that part hard to believe, sorry. I know you race a popular car Dave, I just can;t remember which (you've had a few )

[DaveG28]

Sorry guys, what I may need to say here is when I said about gearing options, I'm potentially getting around a setup issue with gearing too, which I know is a bad idea!

Anyway, don't have a gearing chart here, but the car is the BMax, and I was running 21/81. As a guide with an LRP 6.5 23/81 was only getting normal temps, I took 2 teeth off as I went to the 5.5 Novak. By gearing options I've found I can't mesh a smaller pinion than 21 with the 81 spur, I'd have had to to to the 87 spur, but that won't let me use any higher than a 20 pinion. Off the top of my head I think that equated to knocking about 2.5 off the pinion itself. Correct me if I have that wrong!

Anyway, even on lowest ESC punch (I use LRP TC) I had bad rear traction and didn't like that lack of top end on 21/81 with the Novak, so given the gearing which worked on the 6.5, I decided not to change the gearing down even further!

To be fair to Yok, there will be a 84 spur soon, just not yet, and I don't know what other spurs may fit yet.

Finally, I always get more heat in my motors regardless of the car than most people, and use more current, as I have a nasty driving style!! I made 4600's dump on an astro track this summer!! So I wasn't that worried about the smell short term, recently I had a wheel bind during a heat with another car and melted the insulation tape on my connectors, without damaging the motor, so I wasn't that worried. I'll know better now!

[DaveG28]

Ooh, worth saying one more thing, didn't mean to sound like I was attacking Novak or Yok with my post, having ignored the temp I knew it was probably my cock up, just wondered if thats how a motor would temp fail or should I send it off!

So feel free to laugh at my setup stupidity, but like I say am blaming nothing but myself!!

[Northy]

So what are the overall ratio's on these gearing combinations?

G

[ben]

"how to kill a motor".... give it to rich lowe

[DaveG28]

Originally Posted by Northy

So what are the overall ratio's on these gearing combinations?

G

Northy, can't remember and as above haven't got the gearing chart here!

Based my starting point on Craggs Euro setup, 22/81 on Nosram 6.5 with sintered rotor (12.5mm). I have that same motor/rotor (well, Nosram and LRP are the same aren't they?) and started on the same gearing, but went up to 23t as could afford to lose some more punch and wanted more top end (worked fine!). I then moved down teeth as I moved to the 5.5 motor!

[DaveG28]

Overall ratio 9.06, oops!!! On Novak site they suggest gearing at 11.

[gets coat, closes door on way out]

[Northy]

A little low, but not drastic. I run 9.1 on my 6.5R. Maybe the marginal gear ratio and your aggressive driving caused it.

I'd only drop one pinion to 9.51 on a 5.5R.

Might be worth sending it back for a look at though in case it was a manufacturing fault?

G

[Chrislong]

Perhaps it was over geared, or perhaps you tend to get motors hot. The next thing worth asking is why didn't the ESC/motor thermal protect it, it seems strange to me that it didn't.

I have run a 4.5L and got it stinking hot in 2 minutes, and I just kept letting it thermal, wait 10-20 seconds, then carry on a bit, thermal, wait a bit longer, carry on - I did a full 5 minutes like this. I know I got the gearing completely wrong, and the motor was vastly too fast for the track on a particularly hot day - but doing this did no lasting damage to the motor or the GTB.

Im wondering if there is another fault? So it is certainly worth contacting CML with thorough information, and they will send it to Novak to evaluate.

Chris

[bert digler]

send it back it may be built dodgy as if that would happenafter all you have nothing to lose

[Mike Hudson]

i've done exactly the same with a 5.5L in my 4wd the L motors just get too hot in a 4wd, I fried mine in the wet at teeside regional this summer but the rotor still seem's well magnetised though I got it sent back to novak but they don't cover warrenty on motors that have been burnt out by not being geared correctly to the right temperature so looks you'll have to buy a new motor

[super__dan]

L's get hotter than R's no question, I guess it depends on how you drive, personally I've never had an issue (the exception with the 4.5L and 2wd when Rich Lowe and I were messing around at Teeside the other year). In normal use I've never had an issue running an L motor in 4wd and know lots of others who haven't either.