Nice work. So losing a phase causes much more rapid motor deceleration than grabbing the motor, or does it produce some kind of vibration that is more effective at loosening the prop?
P3P suddenly fell from the sky
- Thread starter Buddy Moran
- Start date
Nice work. So losing a phase causes much more rapid motor deceleration than grabbing the motor, or does it produce some kind of vibration that is more effective at loosening the prop?
I really couldn't say for sure...
Honestly, I have just as much a hard time imagining a birdstrike as I do spontaneous propeller fly off, but I have to imagine both are possible.
I know with certainty the self tightening action works so I can't imagine why, during a seemingly turbulent-free casual flight, that a propellor would fly off unless through failure... be that hub crack leading to separation or motor seizure, which now that I type this could be possible.
I just find it hard to believe, and I stand to be proven otherwise, that an insufficiently tight propellor would spontaneously fly off. Not after the self tightening double rev at startup and the continuing self tightening of the initial climb.
"Once you eliminate the impossible, whatever remains, however improbable must be true"!
Losing a phase instantly locks the motor up solid. If you look at how brushless motors and ESC's work, you will see that at any instant, only two phases are energized. One coil ahead of each magnet will be pulling it. The coil behind the magnet will be pushing it. The coil adjacent to the magnet is used like a sensor. As the magnet passes the center point, the induced voltage triggers the ESC to switch phases to the next set of coils to keep the motor turning. If one wire is disconnected, the signal never reaches the ESC to switch and all magnets and coils are frozen in their current position.
I think that @syotr has demonstrated one clear mechanism by which even a reasonably well tightened prop can be ejected.
I have found that if I installed props really loosely, with a gap between the prop and motor, that when started, the motor would spin up a few revolutions, picking up some speed before the prop bottomed out on the motor shaft. You would hear a satisfying "thunk" when that happened and the prop would be hard to unscrew.
Yep, read that after I posted... that's really what I mean when I say seizure, or motor failure, or some other contributing factor other than the propellor flying off because it wasn't tight enough.
Ive read of many who believe that's possible (simply flying off because it wasn't right enough). That's the one I have a hard time with.
I've posted that pulling your battery out causes two of the props that are rotating in the same direction to fly off. I have no verifiable proof but I'm certain that the sudden power loss contributed to motor behaviour in a way that made the propellers fly off, but I can't prove it.
Maybe the @stotr test replicates the same behaviour I'm trying to describe.
Yes. Like that. Exactly that.
I used to put my props on, snug them, and fly... then take them off. When they came off, they were same level or maybe a little more snug than when I started.
I've since gotten a case that allows me to leave them on all the time.
Since then I check them occasionally, and after a few flights, they are impossible to remove without the motor clamp that came with the package.
Clearly, they are tightening ALL THE TIME.
I've replicated this many time over.
Agreed, although for this, and other reasons, I much prefer the newer bayonet-style hubs.
I am not sure how phase loss would be detected and recorded in a flight log. As far as I know, there is no feedback from the ESC or motor to the flight controller. The flight controller commands a certain motor speed to an ESC to level the aircraft and if the aircraft does not respond accordingly, then it commands increasingly higher speeds until it reaches the maximum set value and then assumes motor failure or prop loss. The only feedback is from the gyros and IMU. I think the flight log only shows a "commanded" speed, not actual. Not sure if phase loss or a MOSFET failure would show up in the flight log.
It is always easiest to blame the pilot, but mechanical and electrical things do fail.
It is always easiest to blame the pilot, but mechanical and electrical things do fail.
Nice mythbusters-like video! Thanks.
My P3P is two years old and I have only ONCE installed the props fearing I might sometime not do it correctly. Fear no more about that.
I have a B&W type 61 DJI 3 hard case for the car and a Anbee Easy Carry Vest for the bike so I can always leave the props attached. So I don't need them to prevent the props-fly-off. But nevertheless I still like them because they save me some time to connect/remove the props.
I had two prop loss incidents on scatch built models. One was caused by a loose bullet connector, the other by a stray bit of solder that touched an ESC. I have a picture captured from video showing the prop spiraling off up into the air as the quad tumbled down. You can see the prop on the left side of the frame.
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Not just you. Shortly after they were released, I had one freak out on me. Confirmed by DJI that it was their technical glitch and they warranty repaired it for me at no charge. Edited to add that this was an area I regularly flew in.
The mode of operation you are describing is applicable to a brushless DC motor/ESC combination as is most commonly employed in the RC hobby. It is not applicable to phantom 3 (and later) AC which employ true sine wave drive, the motors themselves are true synchronous AC with rotation speed being locked to line frequency.
That looked like either an FC or ESC failure. It didnt' appear to lose a prop in the process though.
@jwmcgrath and @sar104, thank you very much for your analyses and hypotheses. They both sound like possible causes for the AC to suddenly drop. Do you think there is enough data to ask for a replacement, since it's still within the warranty period? There's no proof of a bird strike. From your feedback, there doesn't seem to be any definite proof of something external to the P3P that would cause the prop to fly off. A bird strike might be a possibility, but no definite proof.
Can you check if the front right ESC did fail? Even if you can't power up the aircraft, you can check if all the connections look good. If it was ESC failure then DJI may well be willing to repair or replace under warranty. You just need to be able to demonstrate that it was not user error, such as an improperly attached propeller. I'm not sure whether @With The Birds's observation regarding the motor design means that these motors behave differently than demonstrated by @syotr, but it's probably worth pursuing anyway.
Yeah. DJI didn't send me a detailed report as to what went wrong just a (paraphrased) "Ooops. Our bad. Here's a fixed one." note. Took 10 weeks but at least I didn't have to pay for it.
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