Fried motors

Doomed flight is here:

Hobbypartz.com has great prices and great motors. I think. But for some reason I seem to be having some very bad luck frying motors lately.

I've been running one of their 450TH motors rated for 230 watts (http://www.hobbypartz.com/45oubrmo6.html) at exactly 230 watts, and haven't had much issue with very short bursts at the 230 figure of 40 seconds or less for takeoffs.

BUT-- For the first time I flew full throttle the entire flight, mostly due to winds, and the motor and controller both fried. That's 20 amps through at 25 amp controller, 3 cell lipo, which is roughly 230 watts. This outrunner motor is out in the open air, so it shouldn't be overheating.

I know the rule is probably to run way under the motor's rating, but what do you guys think? Is it unreasonable to expect a 230 watt motor should run 230 watts for at least a few minutes? This is the 3rd motor that has done this to me, and I am starting to think that I should be running 80% of maximum as a rule and see if that gets me any better luck.

One possibility though. I have to limit max throttle to 75% to keep the current at the maximum of 20 amps. Could running a controller in this way cause problems?

Thanks for any ideas!

Tj,

the motor in open space does not mean good cooling. Is it mounted on a firewall facing rear (EZ* I guess) ? The air choose the easiest way. The air has to pass through the motor, so better if it is mounted inside a tube, with full air flow forced around and inside it. The same for the ESC.
Anyway it sounds strange.
Do you know the 75% rule ?
ESC 75% overrated, motor 75% overrated (revving at 75% for cruise speed and 100% for reserve), battery rated at 75% C and capacity.
If you have space I would try a lower revs/V motor with bigger prop (or 2S with bigger prop).
I agree with Sys-Ak about Esc settings too : low timing and low PWM (if the motor works with them, but it should).

Best regards,

Ric

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Comments

Tj Bordelon September 27, 2010 at 11:53am

@Hooks - Good point. ESC in the controller would die and kill everything. Not so good. I actually rely on that to power my servos (not the AP). Maybe it's time to trust the controllers less. I'm lucky the internal BEC didn't go!!

@Riccardo - Thanks. I probably need to avoid running at 100% and give the 75% rule a go. I had heard that partial throttle heated the controller and motor but was unsure if this was the case. I think it IS the case.
Riccardo Kuebler September 27, 2010 at 11:34am

... forgot to say that the 60%-90% range is the heaviest range for an ESC, then heating, so it has to be oversised for this reason too.

Ric
Riccardo Kuebler September 27, 2010 at 11:31am

Tj,

the motor in open space does not mean good cooling. Is it mounted on a firewall facing rear (EZ* I guess) ? The air choose the easiest way. The air has to pass through the motor, so better if it is mounted inside a tube, with full air flow forced around and inside it. The same for the ESC.
Anyway it sounds strange.
Do you know the 75% rule ?
ESC 75% overrated, motor 75% overrated (revving at 75% for cruise speed and 100% for reserve), battery rated at 75% C and capacity.
If you have space I would try a lower revs/V motor with bigger prop (or 2S with bigger prop).
I agree with Sys-Ak about Esc settings too : low timing and low PWM (if the motor works with them, but it should).

Best regards,

Ric
Sys-Ak September 27, 2010 at 11:06am

Don't limit the throttle, it won't solve anything. Use a smaller prop instead.
I would also check the timing and PWM settings in the controller. If they are not correct, efficiency can drop and the motor will generate more heat, even with the same power consumption. Oversized prop have the same effect.
Tj Bordelon September 27, 2010 at 10:29am

@Brian - Lipos are Thunder power and I'm using ones I bought over a year ago. Those are running like champs.

I am wondering if the "in flight" load on the motor is higher now. I thought it went down with airspeed due to the decrease in AOA with forward flight. But who knows-- I should probably be logging that data. (I don't).

Thanks! That's a very good question.
Moderator

Robert Krogh (hooks) September 27, 2010 at 10:29am

Last flight I had! The ESC burned - result was very different from the recovery you had. :-(. Without power to the Rx and AP then Houston... we have a problem....l
Moderator

Brian September 27, 2010 at 9:58am

If you are running within the specs of your motors on the bench then it could be the underload numbers are higher and with you running at or near full th then you could be exceeding the specs of the motor for how long it can sustain max numbers. How are your lipo's doing?
Tj Bordelon September 27, 2010 at 9:13am

@Ground loop - I would tend to agree, but one was a Zagi TAZZ that smoked. I haven't ruled out that it isn't me :). Mind you 2 of them WERE the 450TH motors.

If I had to guess, running my motors at 75% throttle may be delivering the max 230 watts on the meter, but this is an average. If I went to 100% I would be at 30+ amps and that would be 300+ watts. Maybe the peaks matter.

It might be a 'me' problem.
Developer

Jani Hirvinen September 27, 2010 at 9:12am

What I have seen and also tested quite many motors lately due ArduCopter project, most of manufacturers gives higher ratings that they motor actually are. And also when you have identical motor from different vendors, values differs sometimes a lot.

So I would not trust so much on those tech details so much. Not even Kv values due even they can be easily -+15%. It's better to test those by your self or try to find test reports that are made by someone else than manufacturer.
Ground Loop September 27, 2010 at 9:06am

If that's the third motor that's done it, I'd ditch that brand altogether!
Too much investment up there in the plane to trust it to a crappy motor.

That's just me.

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