One engine's magnetic resistance feels slightly different...

[Hionimi]

Hi, I'm working on an completely geniune DJI Flame Wheel F450 at the moment, so using the DJI 2212 engines, though I noticed just one feels, different. Not overtightened or bad, just different. Most notable when mounting the propellers and gently pushing them with your finger, the other three engines you get this skipping resistance from the magnets inside, but one engine this seems less. Yet when I test it out (no props for safety) all engines sync nicely during initialization and all seems dandy when I spin them up, but it's hard to tell if the engine in question spins with any less revolutions per minute. Could it indeed be that this engine is less and might need to be replaced or is this nothing to worry about? Don't really want to risk just letting it take off, it might flip...

 

[Cyberdactyl]

You could always do a "String Test".

On my first quad I was pretty much over-cautious and did the test. I have to say, it does give you a bit of confidence during your first true maiden.

 

[Hionimi]

Yeah, I just wish to make sure, this quad is triple the price of my previous one with a completely different controller, crashing is not an option.

 

[Craftydan]

Another thing you can do is a vibe test -- there are some smartphone apps or the laser method -- restrain the copter, disconnect all but one motor, mount the sensor on the boom (mirror or phone), and slowly throttle up. If the motor in question is vibing stronger than the others, it should be pretty obvious.

I had a motor with a berring going out (didn't know that at the time). You could see the vibe in the onboard video, but they all spun and sounded fine. Ran this with a laser, and the troublemaker popped up. Knowing the source (and I could ignore it) I let her continue, keeping watch. After a dozen or more flights, that motor started to get stiff and swapped the motor -- vibe testing can pick up problems long before they become trouble.

 

[Hionimi]

Ah awesome, will try both these test, thanks.

 

[Tritium]

My 6 DJI motors were different too. Made no difference in flight.

Thurmond

 

[Hionimi]

Ah, and it didn't matter if they were connected to the ESC or not? (As, I believe the ESC can change an engine's magnetic strength a little after each run.)

 

[Tritium]

Nothing except heat is likely to cause a change in the flux density of NdFeB magnets. Excessive heat will kill NdFeB magnets.

No change whether hooked up to an esc or not and mine remain the same after many hours of operation.

Thurmond

 

[Hionimi]

Well this is good news then, will keep an eye on that engine just to be sure though, but can just go flying hopefully once the weather allows it.