Monster X and TP4250, motor smokes during KV Test

[Lizard]

Finally tried the Monster X with a brand new TP4250 4Y 1570KV.

First test inside my apartment, started it twice and ran it for like 5 meters with 5kph. No problems.

Then did the Torque Control motor test, spinned it up, after 2 seconds or so, there was smoke coming from the motor cables :( Stopped immediately, touched the cables, they were _not_ hot, just slightly warm, also everything else was cool.

Data log shows 14A peak current, 10A after full RPM has been reached. Isn't 10A a little too much for a 42x81 420g motor? The detected kv value doesn't seem to match the RPM in the datalog, 1869 KV should give 42400 RPM with 22.7V instead of 37600 RPM. Maybe that is because the test was not completed?

Apart from that everything looks normal (?), no high currents, no big voltage drop, no big temp rise. Although the temps seem to be offset around 10C, it was 23C in the room when I started the ESC.

I am a little puzzled, I see smoke, but no high currents, I cannot feel anything being hot or even warm? What's this? Motor toast from the beginning?

Here is the datalog and a video showing everything:



[youtube]http://youtu.be/pL-jO18OHJA[/youtube]
http://youtu.be/pL-jO18OHJA

[phildogg]

Ive also noticed the esc temps are off by atleast 20 deg. its 72 degrees in my house and esc reads 92 or 93 degrees on start up. man you are having some problems lately with motors huh?

[Lizard]

Hmm, that would be about the same difference and temps, just in Fahrenheit.

Yeah, really no luck :(

[Dr_T]

Any word from TP about your motors?

[3905er]

i am curious as to what happened with your motor . I had a similar situation today with a tp 4250 sensored motor. Ran it outside for a few minutes , then gave it full throttle from a standstill and a puff of smoke and no movement ?? emailed tppower for a rma

[bdebde]

Being that many motor manufacturers have statements like this in their manuals "Never apply full throttle if the motor is not installed. Due to the extremely high RPMs without load, the motor can get damaged.", I have never used the torque control feature.

[Dr_T]

Originally Posted by bdebde

Being that many motor manufacturers have statements like this in their manuals "Never apply full throttle if the motor is not installed. Due to the extremely high RPMs without load, the motor can get damaged.", I have never used the torque control feature.

As long as "no-load kv" x applied Voltage does not exceed the motor's max RPM, revving unloaded for a bit shouldn't cause any problems, right?

[Lizard]

Still not sure about that. Have done the Torque Control tests many times with my motors though.

I have once read somewhere that the bearings don't like to be spun without load, they could vibrate or something.

The other thing is that the balls in bearings slip when accelerated too quickly which wears them down faster. The manual of my Novarossi 528XRP nitro motor stated that one shouldn't go from zero throttle to full throttle instantly because the motor spins up faster than the inertia of the balls in the bearing allows for. I.e. the balls don't 'roll' inside the bearing bur 'slide'. Not sure if that effect also applies to brushless motors (bearings being smaller, but motor can spin up even faster than a nitro), I just avoid to spin it up too quickly.

[Dr_T]

The acceleration difference between motor shaft and bearing balls (wtf did I just say, lol) is an interesting aspect, never looked at it like that.

[Pdelcast]

Originally Posted by Dr_T

As long as "no-load kv" x applied Voltage does not exceed the motor's max RPM, revving unloaded for a bit shouldn't cause any problems, right?

That's correct.

And you can always run the Kv test with a lower voltage too... it will still work correctly.

So, if the application is for 4S, you can run the Kv test with 2S if you are worried about overspeeding the rotor.

A lot of cheapy motors out there are skimping on rotor materials -- so the concern is not unjustified.

Patrick

[Lizard]

One more question: Since timing influences kv, do I need to do the Torque Control kv test again after changing timing?

[Pdelcast]

Originally Posted by Lizard

One more question: Since timing influences kv, do I need to do the Torque Control kv test again after changing timing?

Won't be necessary. The torque limiting algorithm compensates automatically.