I was very, very lucky ... (birdstrike?) on Mavic 2 Pro

[Ronny St.]

Yesterday I had a very frightening event. During my flight at 145 m height and a distance of 240 m my Mavic 2 Pro suddenly gave a warning of an upward obstacle. The sky was clear and almost no wind. Then the warnings cascaded with several side and backwards shocks. Seven seconds later the message 'propeller fell off' appeared and in 3 seconds later the drone plunged from 55 m height to the ground, sending several warnings again. I then lost connection since I was on a hotspot connection and had forgotten my smartphone at home (fortunately close-by).
The final height indicated was minus 5.1 meter(?!) and I rushed indoors to get my phone. Luckily, with the help of the blue dot indicating your position I was able to find the drone again. I found it in a field with high grasses due to the blinking red LEDs on the arms.
The left propeller was completely gone and the right arm was folded inwards with the tips of the propeller broken, so I replaced both the front propellers with the spare ones in the box and immediately ordered some extra pairs. I then did a test flight and everything seems to be ok again. But, and this is an incredible coincidence, during the test flight (about 30 minutes after the crash flight) the farmer suddenly appeared on his field with his tractor and a gigantic mower behind it. He started to harvest the high grasses directly in the line where I found the drone. So if I would have found the drone within 30 minutes, it would not only have been completely wrecked, but probably pulverised by the gigantic mower.
I assume it must have been a birdstrike, I don't see any other explanation.
This was my first crash and hopefully my last one, my heart skipped several beats and I realize that I was very lucky to find it again without irreparable damage. I am thinking of getting some decals on the drone, but I wonder if that would have helped to scare the bird(s), if there were any.
All details of the flight can be seen on

 

[Deleted member 77603]

I lost an MP2 to a crow strike. Still haven't found the drone.

 

[Ronny St.]

I lost an MP2 to a crow strike. Still haven't found the drone.

That I was afraid of. I only had 5 previous flights with my M2P (just bought it second hand) so it would have been horror to lose it during the 6th flight while still learning and getting acquainted with the drone.

 

[slup]

Nothing in the log indicates a bird strike... it's much more likely that the left front prop failed & the prop itself came withing the upward OD sensor indication area & triggered a UPWARD OBSTACLE DETECTED message coming at 476,5sec.

The AC attitude change comes very abruptly while you command the AC to fly sideways to the left (a full negative aileron command). At 476,4sec into the flight the AC pitch down & rolls over further to the left... both these movements indicate a thrust loss from the front left corner. This is also supported by that the AC starts to rotate CW, this as the front left should generate CCW rotational torque... so without a prop on the left front a rotational torque imbalance is created, 2 props torque CW & only one CCW... = the AC starts to rotate CW.

 

[Yorkshire_Pud]

Having had a Mavic 2 crash from 50ft I would suggest that you check the front arm pivots do not have a bent pin on their top.
You will need to remove each pivot to check it and I suggest you check them one at a time.
It makes removal and refitting of the pivot easier if the arm is positioned at the tipping point between its desire to spring into the flying position and the storage portion.
BE AWARE there is a black plastic thrust washer trapped between the top of the arm and the underside of the relevant part of the drone's body work, the pin mentioned earlier goes through this washer. With the pivot removed this thrust washer is easily displaced.
At the time of my crash the pivots where readily available and relatively cheap.

Also there is a lug on the inner end of each rear arm pivot, it appears these lugs are quite easy to break. They act as a travel limiter for the arm when the arm is in the flying position, if the lug is broken it CAN NOT BE SEEN during an external inspection but the arm can then rotate beyond the proper flying position.

Removing and refitting the front arm pivots is quite simple but broken lugs on rear arm require replacement of the arm and that meaning the drone has to be opened. If you are inclined to DIY rear arm damage you would do well to watch all the dismantling videos you can find the rear arms can only be refitted when the lug is aligned with a groove in the corresponding bore.

 

[Ronny St.]

Nothing in the log indicates a bird strike... it's much more likely that the left front prop failed & the prop itself came withing the upward OD sensor indication area & triggered a UPWARD OBSTACLE DETECTED message coming at 476,5sec.

The AC attitude change comes very abruptly while you command the AC to fly sideways to the left (a full negative aileron command). At 476,4sec into the flight the AC pitch down & rolls over further to the left... both these movements indicate a thrust loss from the front left corner. This is also supported by that the AC starts to rotate CW, this as the front left should generate CCW rotational torque... so without a prop on the left front a rotational torque imbalance is created, 2 props torque CW & only one CCW... = the AC starts to rotate CW.

View attachment 162765

Thank you very much for this elaborate analysis, Slup! It gives the incident a complete other dimension.
Btw: how did you retrieve that information out of the flight log?

 

[Ronny St.]

Having had a Mavic 2 crash from 50ft I would suggest that you check the front arm pivots do not have a bent pin on their top.
You will need to remove each pivot to check it and I suggest you check them one at a time.
It makes removal and refitting of the pivot easier if the arm is positioned at the tipping point between its desire to spring into the flying position and the storage portion.
BE AWARE there is a black plastic thrust washer trapped between the top of the arm and the underside of the relevant part of the drone's body work, the pin mentioned earlier goes through this washer. With the pivot removed this thrust washer is easily displaced.
At the time of my crash the pivots where readily available and relatively cheap.

Also there is a lug on the inner end of each rear arm pivot, it appears these lugs are quite easy to break. They act as a travel limiter for the arm when the arm is in the flying position, if the lug is broken it CAN NOT BE SEEN during an external inspection but the arm can then rotate beyond the proper flying position.

Removing and refitting the front arm pivots is quite simple but broken lugs on rear arm require replacement of the arm and that meaning the drone has to be opened. If you are inclined to DIY rear arm damage you would do well to watch all the dismantling videos you can find the rear arms can only be refitted when the lug is aligned with a groove in the corresponding bore.

Thank you for contributing to this topic, Yorkshire_Pud. I must admit that some of the technical terms here make it difficult for me to follow your advice. As my native language is Dutch, I do my best to express myself in English, but if it gets more specific it is not easy for me to grasp what is meant.
I dare to say that I am quite handy to repair stuff myself but I must know what I am doing before making it worse than it was before I have been searching for it, but I only find videos how to remove and replace the front arms, as there is e.g.

at 1 min 30 sec or

Is there maybe some YouTube where it shows how to remove the front arm pivots to just check them without having to remove the complete front arms?
At this point, I don't dare to fly it again as long as I'm not sure that everything is ok and that I'm not risking to have the same bad experience again.
Thanks for helping me, I know you also reacted in my other topics, so I am very grateful to experience your kindness again!

 

[Yorkshire_Pud]

Incidentally what controller do you use? If you DO NOT sync your logs and use either the smart controller or the RC1A controller then there should be a DAT log on the screen device and the DAT records motor speeds. If you use an RC1B controller and or sync then I think there will be no DAT on the screen device.

 

[Ronny St.]

Incidentally what controller do you use? If you DO NOT sync your logs and use either the smart controller or the RC1A controller then there should be a DAT log on the screen device and the DAT records motor speeds. If you use an RC1B controller and or sync then I think there will be no DAT on the screen device.

I am using a smart controller.

 

[Yorkshire_Pud]

I must admit that some of the technical terms here make it difficult for me to follow your advice. As my native language is Dutch

ahh ok. You English is fine.
I will break this into two or three posts the first of which deals with the front arm pivot.
In the first video you might have noticed that around 3:50 the guy twists the base of the front arm pivot relative to the silver bit so that the assembly sort of sticks 'midway' between the two positions the spring inside the pivot tends to force the assembly to take. He then positions the arm partially open and the pivot more or less drops into place. I call the 'sticking point' the tipping point. I do not like the tool he used to grip the silver bit, the tool appears to be too thin for my liking and might dent the silver bit.
I used either
a) two proper pliers, one pair to grip the silver bit and the other pair to twist the base
or
b) I pulled the arm slightly out of the drone and dropped the pivot into the 'square' hole in the arm itself, I then held the arm and twisted the base of the pivot with pliers.

To remove the pivot remove move the arm to the approximate position shown at around 4:11, if you get the position correct the arm will sit there and NOT want to move to the storage position or the flying position. It will probably take a bit of trial and error to get the position correct but do not let the arm jump to either the storage position or the flying position when 'testing' whether or not you positioned it correctly, I do not think the thump at the end of a jump is good for the drone.
In the 1st video he does not need to do that because the pivot is broken and 'falls apart'.

That I can see he does not check whether or not he has displaced what I called the "black plastic thrust washer" (it's just a black plastic washer, of a certain size, that fits between the the two of the arm and the drone's body.)

 

[Yorkshire_Pud]

With regards to the second video, you will notice that he fits the new arm with the arm more or less in the storage position, this is so that the lug /bump/ protrusion on the male part of the arms pivot aligns with groove that runs down the bore / inside of the female part of the pivot in the drone. I will leave it there for the moment and see if I can dig out some bots to photograph and show you what I am taking about but that may take a couple of hours, bear with me

 

[Ronny St.]

Super! Thanks for the compliment on my English, I am doing my best
I will wait until further info and start with the procedure from the moment I know for sure what I am doing. Thank you again for your help and cooperation!

 

[Yorkshire_Pud]

Note. I spotted what turned out to be the bent pin on the pivot of one front arm because the affected arm drooped when compared to the other arm. If both front arms are symetrical post a photo of them looking front the front and at the drone's nose.
If you end up having to replace rears arms and also replace the female half/halves of the pivot/s watch you do not displace the rear ventilation grills, I noticed recently that I have displaced/rumpled the one by the female pivot I removed and refitted. If the rear arms DO NOT rotate upwards from their flying positions then it is likely the "lugs" are ok. My rear arm rotated upwards slightly when I throttled up to make the drone climb.

 

[Yorkshire_Pud]

With regards to the smart controller and the DAT, if you manually uploaded that txt flright log to Airdata then have a look in the folder where you found the .txt flight log.
In that folder you should find a folder with the name "MCDatFlightRecords". If the DAT still exists it will be in that folder and have a name that probably contains FLY006.
If you uploaded the txt flightlog to Airdata via some other means you might need to have a look at post #2 of Download logs from Mavic 2 Pro & SmartController for instructions concerning where to flind the logs, I do not know if the procedure layed out there is still correct.

 

[Ronny St.]

Wow, what an effort you made for me: thank you!
I took a photo from the front as you requested:



I must say everything 'feels' ok, that is, the arms nicely 'click' into place when opening or closing them, but one never knows if there is something wrong that can not be seen from the outside.
Could it be that I did not attach the front propeller properly and that this was the reason he just released during the flight? In any case it could of course damage the arms or other parts during its fall and collision with the earth. Fortunately the drone fell in high grasses and not e.g. on hard concrete.
And the test flight I made with the spare set of propellers that came with the drone did not indicate anything wrong.
But I will follow your recommendations you will give me, as I have all confidence in your motives

 

[Ronny St.]

With regards to the smart controller and the DAT, if you manually uploaded that txt flright log to Airdata then have a look in the folder where you found the .txt flight log.
In that folder you should find a folder with the name "MCDatFlightRecords". If the DAT still exists it will be in that folder and have a name that probably contains FLY006.
If you uploaded the txt flightlog to Airdata via some other means you might need to have a look at post #2 of Download logs from Mavic 2 Pro & SmartController for instructions concerning where to flind the logs, I do not know if the procedure layed out there is still correct.

I'm afraid I had the flight logs set to synchronize automatically... Should I turn it off for future flights?

Edit: I checked it and found a DAT file with FLY006 in the name, as you told me
I will attach it here. I had looked to those files before, but it automatically opens Cyberlink Photo Director 8 and tells me the file cannot be opened. So I do not know what software I have to use to open it nor what can be found in DAT files

 

[twickers14]

This thread personifies the fantastic support those of you who know what’s what and those of us who fly but with little if no knowledge of how everything works (or doesn’t work). Thanks all.

 

[FLDave]

@Ronny St. Everyone has a preference for managing flight log files: synchronize or not. My preference is total control so I download the .txt and .dat files each day from my device (smart phone) to my computer and then upload the .txt files to AirData. That way I have the files on my computer and know exactly where they are and can be easily accessed if and when needed.
The .dat have no value to me as they are encrypted but I keep them anyway.

 

[Ronny St.]

This thread personifies the fantastic support those of you who know what’s what and those of us who fly but with little if no knowledge of how everything works (or doesn’t work). Thanks all.

True, but I am willing to learn as much as possible from those who know a lot more of that matter than I do

 

[Yorkshire_Pud]

Should I turn it off for future flights?

It's personal preference, I want the DATs and I don't want someone else holding my flight history so I have only synced a very few logs.

To me your drone appears to be low on its right hand side and it looks as if the right rear arm is touching the table whereas the left rear arm is not. A quick glance at mine suggests that both rear motors should be clear of the table top.

Though I would wait and see what others think.

With regards to what happened to the prop,
It's difficult to say, do you normally remove the props at the end of a day's flying?

If the props are not properly fitted, meaning they have not been rotated far enough for them to lock into place, then the shaft that runs through their centre sticks up above the top of the prop's hub.
When the prop is correctly fitted then the top of the shaft is flush with, or perhaps slightly below, the top of the prop's hub.

Also for an incorrectly fitted prop to be thrown in the release direction, let's call that forward, the motor would have to deccelerate very rapidly. Plus the drag (air resistance) of a spinning prop would tend to move it 'backwards', in the direction to make it 'lock' as would motor accelerations.

Given that the props can 'bite' I am not inclined to try incorrectly/ incompletely fitting a prop to see whether any deccelerations are strong enough to throw a prop forward.
Could the catches of a prop break?
I have had one out of the three catches on each M2P/Zprop break in an indoor mishap but when inspecting the drone the motor of that prop felt rough and I think the catch fragment was catching on the motor windings.

There are at least two threads where 'mavic' props broke, at the hub, in mid air but they were/are, I think, Air or Air 2 or Air 2s and I think they have only to catches per prop. The M2P has three catches so might be more secure. At least one of those 'Air lodt a blade but remained airborne and with difficulty controllable and it was brought home. I did test a M2P with half a blade cut off, from memory the drone remained controllable if the butchered prop was on the rear but was uncontrollable if that prop was on the front. Those tests were indoor flights and literally take off or try to take off, climb to a height of a couple of inches see how it handled for a few seconds then land. The upward looking vision sensor registered the ceiling and kept the drone low.