Lucky save

Was flying around taking some photos and heading towards the shore to take pictures of an abandoned boat midning my own business. Got close to the beach and suddenly an alert for magnetic perturbance popped up.

I still had some control over it trying to fly it back and change altitude in a hope that it would stabilise. I was worried it’ll fall in the water, but I did manage to bring it inland. Changing altitude (what little I had control over it) didn’t make any difference either, poor little thing was going all over the place. Luckily it then decided to make an uncontrollable slide along the footpath until the crash right next to it. I knew roughly where it landed but not how far from the path until I heard the distress signal and found it right by the path.

Damage? One broken propeller and couple scratched. Interestingly, the log shows “motor broken” alert, but after replacing propellers I made a test flight and everything is okay.

The logs make no mention of a “magnetic perturbance” … only “motor broken”.


I don’t know how old the drone is, but that - mid flight - might be a warranty claim.

I certainly wouldn’t put new props on and fly it again.

Yeah, that’s the baffling bit. The rermote threw magnetic perturbance alert a second before it went out of control, and the logs say that the motor is broken. Also there is that “Unknown or Undetermined” error. I’m not really sure which one to believe so I think I’ll just fly for now. When I got home, I flew about 10 minutes without any issues leading me to believe the motor broken warning is incorrect.

I bought this used and it wasn’t very expensive so monetary loss will be neglible if I lose it.

I’m new to all this airdata stuff, but it seems wierd that your altitude shows as continually climbing, even at the end when it came done the barometer alt is 800+ meters.

The altitude is way off for some reason, my guess is the perturbance caused it. When the trouble started, on the controller, it showed correct altitude however (I was about 15 metres up).

After it went mad, I was still able to steer it somewhat, for example when I pressed RTH, it started to gain altiude (I’ve set mine to 50 metres) and turned towards home point for a second or two. When that failed, I tried first to gain more altitude (it was never higher than about 30 metres) to get away from the perturbance and pull it back towards me. It was pretty impossible however, the drone was going in all directions spinning and going up and down randomly so I gave up when I saw it was heading north over land.

The motor failure alert is really weird, I would assume the thing would fall down more or less like a rock if one of them cuts off, but you can see it flew quite a distance in steady(ish) downward slope.

It’s a shame I didn’t have time to switch to recording and film the whole episode, I was too busy to try to gain control over it.

In the end of the day, I was lucky it landed near the footpath and on a thick layer of whatever them plants (sea purslane I guess) are growing on the marsh.

I suspect it thought it had a magnetic perturbance when the prop started failing due to uncommanded yaw showing on the compass.

Ah! That could be it. Still, doesn’t quite explain the distance it flied after the alert. Do you think if a propeller is loose could cause a motor failure alert? When I replaced them, two screws weren’t quite as tight as on other propellers.

The drag, lift, and weight characteristics of that rotor (the whole prop and motor assembly) will change when a prop fails and the RPM of the motor will also change as a result. The firmware might detect that as a motor failure. I’ve seen it happen on videos of DJI drones where a prop has failed and it’s shown as a motor fail. I don’t think the motor fail warning shows on most drones after a total failure of the motor but when it’s not performing as the firmware expects.

That would explain it then, and the distance it managed to fly after the alert. Especially since there were no issues after I replaced the propellers and flew test flights. A lesson to learn.

Have to add “check propeller screws” to my pre-flight check list :grinning:

Make sure they’re secured with a small dab of locktite too. Many replacement screws come with some already on though.

You always learn something new! Thanks for the tip.

I would suspect a bird strike, it would explain why the drone is ok now

Possibly lost part of a prop when you hit the bird :man_shrugging:

look at this video

If there had been them around, yes, it could have been. In this instance there was only one bird that flew past it, below and about 50 metres away so that couldn’t have been the cause. The loose propeller explanation by @Dorje seems to be the most likely reason. The propeller most likely broke at landing (it was hard enough to push one arm to storage position).

Was the screw loose when you changed it?

Did you watch the video?

As I mentioned in earlier post, screws for couple propellers weren’t as tight as the others. Now, I don’t know what is the correct tightness, but I think they could have been loose enough to allow propellers to “slip”.

I did watch the video and apart of the drone on it being sligthly more stable than mine, the behaviour at the half way mark is pretty much the same. Mine went from smooth flying to completely uncontrollable in a split second. Also, even when I let off the sticks, the drone kept going all over the place.

Only warning I got was the magnetic perturbance alert (of course, different make drones have different features). There are couple spots I can fly over and I know I will get that warning no matter the weather so I know to steer well away from them.

Could the propeller have snapped in flight by itself? I guess it is one possibility too although none of them had any visible markings (never hit a thing).

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If they’re loose they’ll experience more shear stress and vibration, so yes. Couple this with how drones like this use centrifugal force to lock the props in position for flight and two loose props knocking against each other will do some damage over time.

Loctite Blue, it’s what they use on glasses screws and I’m sure DJI prop screws are coated with it. Designed to be released with common tools. Loctite red is a more permanent fix.

I would say yes, looking at the picture that prop does not look loose and if it had become loose I suspect it wouldn’t take long at the rpm until it turns to detach. Also from experience, if it broke on landing you usually find it nearby

but I guess you will never know!

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Have you contacted the manufacturer? Reading the replies to your query it seems you have the answer but perhaps Parrot can confirm (or not!) if the drone can differentiate between magnetic interference and a broken prop.

Possibly too much to do every time but dare I suggest flexing the props lightly to check for hairline cracks before and after every flight.

Thanks! I was about to go and get a bottle from Toolstation tomorrow, but that is red of course. Another mistake avoided.

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