Crashed my Mavic, but why? Can someone help?

[manuelk]

Hi guys!
It's my first post in this forum but I'm a silent reader (and admirer) since I got my Mavic in April this year.
So today it happened to me: I had my first crash. I just don't fully get what actually happened and that's why I need the expertise of more experienced pilots than me. Unfortunately I have no video of the crash itself ... next time I will always start video before take-off and landing ...

I'll put a video of the flight log here (it has also some voiceover of me to explain a bit further what happened):

Also I add the UAV Airdata link to examine more information: Airdata UAV - Flight Data Analysis for Drones

So what happened: I flew my mavic in a sports court with no people around (except my two friends who were with me) and it was quite an open field with like 5-10 meters in each direction. I waited until I had the green GPS status and it told me "ready to fly". I never fly with ATTi especially when surrounded by buildings.
Soon after I lifted off and rised a few meters my Mavic was drifting straight into the direction of the wall. I don't know why the log shows it goes backwards as a first move, because before that it almost went into the wall of the building in front of it.
So of course I panicked a little, I just wanted it to go down to check what's wrong so I pushed the left stick down to land it. While I did this I also tried to avoid flying into one of the surrounding walls but my Mavic hardly responded to my input except for the lowering altitude command. Weird thing is that going down was way slower than what I usually know from my mavic - usually it goes down quite fast until it stops shortly and goes to landing mode. But this time it just went down very slowly for the whole altitude. It didn't even realize the floor was that close in the end. I have been in P mode, not Sport mode, so the look-down sensors should have worked, right?
Anyway in the end it was going down but still drifting rapidly to the right side, shortly before it hit the wall it touched the floor and ripped away some rubber on one landing feet and lost one of the black round things that cover the screws on the backward legs. (Never to be found again)
The following crash into the wall scratched the plastic and the camera (not the lens fortunately), and also slightly damaged some of the props. I tried again to fly at the same area but after the crash I didn't get a green GPS status anymore, so I changed the location and tried again. Everything seemed fine, the Mavic hovered at place for 15 minutes and everything seems normal now. One of the propellers is not turning completely flat anymore - it looks like a very small unbalance or a slight angle at the rotation center. I dunno, as long as it flies it should be okay. But still I would like to know what happened and what I possibly did wrong. Would DJI come up with a free check and repair for that kind of stuff?

My god, I hope you understood my English. It's not my native language and speaking about such a specific topic like flying a drone and describing an accident is not that easy for me.

Anyway thank you for your help! You're the best!

 

[Ty]

My god, I hope you understood my English. It's not my native language and speaking about such a specific topic like flying a drone and describing an accident is not that easy for me.

I can only comment on this. Your English is great!

I hope the veterans and experts can chime in on your issue.

 

[james_mav]

Hi guys!
It's my first post in this forum but I'm a silent reader (and admirer) since I got my Mavic in April this year.
So today it happened to me: I had my first crash. I just don't fully get what actually happened and that's why I need the expertise of more experienced pilots than me. Unfortunately I have no video of the crash itself ... next time I will always start video before take-off and landing ...

I'll put a video of the flight log here (it has also some voiceover of me to explain a bit further what happened):

Also I add the UAV Airdata link to examine more information: Airdata UAV - Flight Data Analysis for Drones

So what happened: I flew my mavic in a sports court with no people around (except my two friends who were with me) and it was quite an open field with like 5-10 meters in each direction. I waited until I had the green GPS status and it told me "ready to fly". I never fly with ATTi especially when surrounded by buildings.
Soon after I lifted off and rised a few meters my Mavic was drifting straight into the direction of the wall. I don't know why the log shows it goes backwards as a first move, because before that it almost went into the wall of the building in front of it.
So of course I panicked a little, I just wanted it to go down to check what's wrong so I pushed the left stick down to land it. While I did this I also tried to avoid flying into one of the surrounding walls but my Mavic hardly responded to my input except for the lowering altitude command. Weird thing is that going down was way slower than what I usually know from my mavic - usually it goes down quite fast until it stops shortly and goes to landing mode. But this time it just went down very slowly for the whole altitude. It didn't even realize the floor was that close in the end. I have been in P mode, not Sport mode, so the look-down sensors should have worked, right?
Anyway in the end it was going down but still drifting rapidly to the right side, shortly before it hit the wall it touched the floor and ripped away some rubber on one landing feet and lost one of the black round things that cover the screws on the backward legs. (Never to be found again)
The following crash into the wall scratched the plastic and the camera (not the lens fortunately), and also slightly damaged some of the props. I tried again to fly at the same area but after the crash I didn't get a green GPS status anymore, so I changed the location and tried again. Everything seemed fine, the Mavic hovered at place for 15 minutes and everything seems normal now. One of the propellers is not turning completely flat anymore - it looks like a very small unbalance or a slight angle at the rotation center. I dunno, as long as it flies it should be okay. But still I would like to know what happened and what I possibly did wrong. Would DJI come up with a free check and repair for that kind of stuff?

My god, I hope you understood my English. It's not my native language and speaking about such a specific topic like flying a drone and describing an accident is not that easy for me.

Anyway thank you for your help! You're the best!

I'm no expert but I imagine electrical interference was the cause of the crash. Have you used this location for previous flights?

 

[manuelk]

I'm no expert but I imagine electrical interference was the cause of the crash. Have you used this location for previous flights?

No, it was my first time. But I had no interference warning and if you check the Signal strength in the UAV flight data you see it is "good" all the way.

 

[james_mav]

No, it was my first time. But I had no interference warning and if you check the Signal strength in the UAV flight data you see it is "good" all the way.

Download the DAT file to this thread & one of the experts can give you more info. How to retrieve a .DAT

 

[manuelk]

Download the DAT file to this thread & one of the experts can give you more info. How to retrieve a .DAT

Good call! It should be the file I attached to this reply.

 

[manuelk]

Nothing new here? :-/

 

[facasi]

Apparently could be related to a magnetic interference or bad compass calibration around metallics or building with concrete rebar.

 

[manuelk]

Apparently could be related to a magnetic interference or bad compass calibration around metallics or building with concrete rebar.

Yeah I know about that issues – that's why I made sure to attach my UAV data where it can be seen that signal and compass was fine. Only the GPS was kinda ****** up, but before start it told me it's fine and it recorded the Home Point correctly.

 

[facasi]

Did you calibrated the compass before taking off in that area ?

 

[manuelk]

Did you calibrated the compass before taking off in that area ?

Nope, I didn't. Usually I assume everything is fine if my app shines the green "Ready to go" towards my face.

 

[geigy]

Wait and see what some of our experts say, but are my thoughts.

The nearby tall buildings reflected the GPS signal from some of the satellites, and the Mavic calculated an incorrect GPS location at take off time, and reported this to you as a green GPS lock. This is an unstable situation. A few seconds later, the calculated GPS position changed, the Mavic interpreted this as a position error and attempted to get back to where it thought it should be. Your controls had very little effect because they were changing the desired location, not the location of the actual drone. I hope this makes sense.

For situations like this, it would be good if the Mavic supported manual override - going to ATTI or OPTI mode. For some reason DJI has not done this. I suspect it is because so many crashes are caused by people using ATTI mode and losing their drone because they did not understand ATTI mode.

For now, all we can do is avoid tall buildings and cliffs, and do our best to make sure we have a good GPS lock. If your phone or tablet has GPS, make sure that the H symbol is where you expect it to be on the map, and the arrow representing the Mavic is located on top of the H. This is still not a guarantee, but it will help the odds.

 

[Lopez0015]

Hey do you unfold completely the propellers?
The way you said the drone behavior ..it touch the ground one side first ..

 

[manuelk]

Wait and see what some of our experts say, but are my thoughts.

The nearby tall buildings reflected the GPS signal from some of the satellites, and the Mavic calculated an incorrect GPS location at take off time, and reported this to you as a green GPS lock. This is an unstable situation. A few seconds later, the calculated GPS position changed, the Mavic interpreted this as a position error and attempted to get back to where it thought it should be. Your controls had very little effect because they were changing the desired location, not the location of the actual drone. I hope this makes sense.

For situations like this, it would be good if the Mavic supported manual override - going to ATTI or OPTI mode. For some reason DJI has not done this. I suspect it is because so many crashes are caused by people using ATTI mode and losing their drone because they did not understand ATTI mode.

For now, all we can do is avoid tall buildings and cliffs, and do our best to make sure we have a good GPS lock. If your phone or tablet has GPS, make sure that the H symbol is where you expect it to be on the map, and the arrow representing the Mavic is located on top of the H. This is still not a guarantee, but it will help the odds.

Yeah I definitely learned my lesson. It's hard to avoid buildings and stuff around you in HK but next time I will be more careful about the shown numbers and odd behavior. Also compass calibration. I just learned about the toilet bowl effect. I'm just glad this never happened before. I flew on some spots where this kind of behavior would have annihilated the drone for sure - and the destroyed drone alone would have be the best case outcome ...

 

[manuelk]

Hey do you unfold completely the propellers?
The way you said the drone behavior ..it touch the ground one side first ..

Of course, haha!
It touched ground one side first because it came down while still drifting to one side so the mavic was slightly tilted.

 

[geigy]

You have some beautiful areas out over the water there. Water is good for drone flying - clean GPS, good signal, lots of good things to see and very little chance of hurting anyone if you happen to crash.

 

[manuelk]

You have some beautiful areas out over the water there. Water is good for drone flying - clean GPS, good signal, lots of good things to see and very little chance of hurting anyone if you happen to crash.

Cool. I will consider that option.

 

[Mad_Angler1]

Good call! It should be the file I attached to this reply.

Thew dat file does not work for me.

can you post it not zipped up, just the file for that flight .

 

[manuelk]

Thew dat file does not work for me.

can you post it not zipped up, just the file for that flight .

Actually I can't. The forum tells me the file type is not supported. That's why I zipped it in the first place.

 

[BudWalker]

Good call! It should be the file I attached to this reply.

That's not the right .DAT. Look here to see how to pick the right .DAT. Even if it's zipped it may be too large to attach to a post. You'll have to Dropbox or GoogleDrive it and post a link instead.