Why did my Mini 4 Pro crash?

[aeciolemos]

Hi everyone,

I was having so much fun flying my new Mini 4 Pro. I love everything about it. I watched countless videos of people having it follow them, avoiding all types of obstacles.

I had obstacle avoidance on, I was flying it relatively close to me, I engaged active track and I told the drone to stay at my 7-8 o'clock and follow. I started walking (I forgot to hit the record button) and after some 2 min, I hear the crash and see the drone in the grass.

I have no idea why it would crash since my left was clear of obstacles, except a few light poles, and I did tell it to stay to my left, since there were trees to my right. It is a pitty the camera was not recording (nor was I screen recording). I uploaded the logs and here is the link:


I have sent it back to DJI under both warranty and care refresh for their investigation. However, I wanted to know more before they come back to me.

Any comments are welcome.

 

[Yorkshire_Pud]

Make the entire Airdata page public or, better yet, download the "original" and upload it to DJI Flight Log Viewer | Phantom Help then post the URL here.

 

[aeciolemos]

Sorry, first time I use airdata
I think I clicked everything except serial numbers.
Here is the other data

DJI Flight Log Viewer | Phantom Help

Upload and view flight logs from your DJI drones

www.phantomhelp.com

I see these two errors towards the end of the logs:
Aircraft battery level low. Return to home promptly (Code: 1B030014).; Motor stuck. Check for objects blocking motor or contact DJI Support for assistance (Code: 30165).; Not enough force (ESC error).
and
Not enough force (ESC error).

I don't think it was my fault, I mean, I wasn't even piloting, so I am hopeful DJI will come back with no cost on the repairs.

Let me know if you see anything.

 

[slup]

The sad truth is that logs will be of zero use as you were in a automated mode... in those modes we can't tell why the program decides to act in a particular way.

The only take away from incidents involving fully automated modes is that you should stay far, far away from obstacles, always be prepared to intervene... & that DJI's marketing material & what you see on YT not necessarily needs to be true.

 

[aeciolemos]

Thank you, understood. I had the same impression, reading the logs. Nothing much there. Also, lesson learned on obstacle avoidance. Big things, sure, trees, not safe.

 

[Yorkshire_Pud]

I would ask where were you when it crashed and is the track accurate? In the satellite view it runs very close to those trees.
I am wondering if a prop blade clipped a branch or twig and then failed.
Did you hear any noises before the crash?

 

[Luckyguy9]

Sorry, first time I use airdata
I think I clicked everything except serial numbers.
Here is the other data

DJI Flight Log Viewer | Phantom Help

Upload and view flight logs from your DJI drones

www.phantomhelp.com

I see these two errors towards the end of the logs:
Aircraft battery level low. Return to home promptly (Code: 1B030014).; Motor stuck. Check for objects blocking motor or contact DJI Support for assistance (Code: 30165).; Not enough force (ESC error).
and
Not enough force (ESC error).

I don't think it was my fault, I mean, I wasn't even piloting, so I am hopeful DJI will come back with no cost on the repairs.

Let me know if you see anything.

I'm not an expert on flight logs, but your first warning was at 16 minutes and 25.1 seconds when your voltage dropped below 7 V. I think the return to home warning comes automatically when your voltage goes below 20%.
You flew for an additional 4 to 5 minutes after you got the low battery warning and I don't know if the motor stuck warning comes when the battery gets critically low and one of the motors just fails to spin.
You can't fly on three propellers, I have seen the motor stuck warning before and that usually means debris in the motor like particle matter, sand, etc. or if a motor stops due to hitting an obstacle.
I'm sure someone else here is better at interpreting these logs than I am. Let's see what they say.
What was the damage to the drone?

 

[aeciolemos]

Hi @Luckyguy9 I did indeed fly past the first low battery warning, but I have done that since the Mini 2. I usually go to the second warning, but never to the critically low warning. Unless the battery had some issue, it still had about 5min flight time until critical. I wanted a last shot But maybe I pushed the Mini 4 too far. I did that to the Mini 2 all the time.

Well, let's see if anyone else sees anything I could not see and I will wait for DJI to come back (I sent the drone in today) and tell me what happened. In any case, I will get a fixed or new drone back, since in the very worse case, I have the Care Refresh on it (I never leave home without it).

Thanks for your input!

 

[Yorkshire_Pud]

let's see if anyone else sees anything I could not see a

post #6

 

[Meta4]

I don't know if the motor stuck warning comes when the battery gets critically low and one of the motors just fails to spin.
You can't fly on three propellers, I have seen the motor stuck warning before and that usually means debris in the motor like particle matter, sand, etc. or if a motor stops due to hitting an obstacle.

That warning message shows at the same time as other data which indicates a collision impact.
It's a symptom of a crash and not evidence of a cause.

 

[aeciolemos]

I would ask where were you when it crashed and is the track accurate? In the satellite view it runs very close to those trees.
I am wondering if a prop blade clipped a branch or twig and then failed.
Did you hear any noises before the crash?

Oh, sorry @Yorkshire_Pud , I had not seen your reply.
I was in front of the drone walking ahead and had active track on. It was a path through the park with trees to the right. I put the drone at my 7-8 O'Clock (southwest) so it would be clear from the trees.
I thought it had hit a branch but it should not have been anywhere near the trees. I did hear the drone crash to the ground but nothing like propellers hitting a twig or branch (snapping sound).


When it crashed, I was aproximately as in the picture above. I had put it to follow me behind left so it would not be near the trees.
I wish I had recorded it or screenrecorded, but it was the last thing I wanted to do that day and I was going to land shortly after this.

 

[aeciolemos]

That warning message shows at the same time as other data which indicates a collision impact.
It's a symptom of a crash and not evidence of a cause.

I guess it did crash into something. It is strange because I would expect the obstacle avoidance to have kicked in. Also, with the Mini 2, when the battery was critically low, it would force landing, not fall out of the sky, and I assume it is the same with the Mini 4. So, my conclusion is a colision with something, but I don't know why it would even have gone near the trees, if I selected it to follow over the part that has no trees. Since I had my back to it and I wasn't looking at the screen (so the video would look more natural), I can't say for sure what it did.
I found a photo of when I set it to follow me. Here you can see what position it was in. Nowhere near the trees! So unless it circled around behind me (on it's own will?) I don't see why it would be near the trees.

 

[Meta4]

I guess it did crash into something.

No guessing is required.
The pitch, roll and yaw data clearly shows a collision impact at 20:56.8

It is strange because I would expect the obstacle avoidance to have kicked in.

Obstacle avoidance is good, but it's not magic.
Page 59 of your drone's manual has a list of things that can be difficult for the obstacle avoidance system.

The vision systems cannot accurately identify large structures with frames and cables, such as tower cranes, high-voltage transmission towers, high-voltage transmission lines, cable-stayed bridges, and suspension bridges.​

• The vision systems cannot work properly near surfaces without clear pattern variations or where the light is too weak or too strong. ​

The vision systems cannot work properly in the following situations:​

a. Flying near monochrome surfaces (e.g., pure black, white, red, or green).​

b. Flying near highly reflective surfaces.​

c. Flying near water or transparent surfaces.​

d. Flying near moving surfaces or objects.​

e. Flying in an area with frequent and drastic lighting changes.​

f. Flying near extremely dark (< 10 lux) or bright (> 40,000 lux) surfaces.​

g. Flying near surfaces that strongly reflect or absorb infrared waves (e.g., mirrors).​

h. Flying near surfaces without clear patterns or textures.​

i. Flying near surfaces with repeating identical patterns or textures (e.g., tiles with the same design).
j. Flying near obstacles with small surface areas (e.g., tree branches, and power lines)

 

[slup]

Got the impression that you knew that the drone clipped a light post & wondered why as you had seen clips showing others flying in between far more obstacles than you in active track...

Where was the light posts located?

The drone slightly pitch down together with a slight roll to the left... & a slightly delayed CW rotation movement when the crash starts. Motors is reported to be on... & the drone don't go down rotating as if one corner doesn't generate thrust anymore (damaged prop or malfunctioning motor). All point to that something hits the front left corner.

All errors in the end relating to stuck motors & not enough force is related to the collision & not a cause to the incident.

 

[aeciolemos]

No guessing is required.
The pitch, roll and yaw data clearly shows a collision impact at 20:56.8

Obstacle avoidance is good, but it's not magic.
Page 59 of your drone's manual has a list of things that can be difficult for the obstacle avoidance system.

The vision systems cannot accurately identify large structures with frames and cables, such as tower cranes, high-voltage transmission towers, high-voltage transmission lines, cable-stayed bridges, and suspension bridges.​

• The vision systems cannot work properly near surfaces without clear pattern variations or where the light is too weak or too strong. ​

The vision systems cannot work properly in the following situations:​

a. Flying near monochrome surfaces (e.g., pure black, white, red, or green).​

b. Flying near highly reflective surfaces.​

c. Flying near water or transparent surfaces.​

d. Flying near moving surfaces or objects.​

e. Flying in an area with frequent and drastic lighting changes.​

f. Flying near extremely dark (< 10 lux) or bright (> 40,000 lux) surfaces.​

g. Flying near surfaces that strongly reflect or absorb infrared waves (e.g., mirrors).​

h. Flying near surfaces without clear patterns or textures.​

i. Flying near surfaces with repeating identical patterns or textures (e.g., tiles with the same design).
j. Flying near obstacles with small surface areas (e.g., tree branches, and power lines)

I trusted both the tracking and obstacle avoidance, after seeing so many on YouTube walk through woods with the drone following them, without a problem. I did position it far from the trees and thought it would follow from that side, as you can see in the picture.

 

[aeciolemos]

Got the impression that you knew that the drone clipped a light post & wondered why as you had seen clips showing others flying in between far more obstacles than you in active track...

Where was the light posts located?

The drone slightly pitch down together with a slight roll to the left... & a slightly delayed CW rotation movement when the crash starts. Motors is reported to be on... & the drone don't go down rotating as if one corner doesn't generate thrust anymore (damaged prop or malfunctioning motor). All point to that something hits the front left corner.

All errors in the end relating to stuck motors & not enough force is related to the collision & not a cause to the incident.

I am not sure how it crashed. I think it hit something but I can't understand why. I don't think it hit the light pole, it was between me and where the drone should have been. The issue is, I had my back. I did not see where it went and I did not record it. I wish I had.

I have been flying for 5 years. I never used anything with active tracking or obstacle avoidance, always flying on manual mode and I have never crashed. I know to avoid power lines and twigs. I trusted the obstacle avoidance and active track. I was playing around with it.

From your description it does seem it crashed into a light post, but wouldn't that be something it should know to avoid? Having said that, the greatest mystery for me is why it circled back behind me if I clearly set it to follow me from the southwest, as I put in the pictures. It should have stayed well clear of both the lamp posts and the trees.

In conclusion, my greatest question is why it crashed. Why did it go where it was not told to or not supposed to. And why did the obstacle avoidance not avoid the crash?

 

[aeciolemos]

Ultimately, I want to learn what not to do. I clearly did something wrong there and I don't know why it crashed.

I had seen this video and it seems to deal well with branches and twigs, contrary to my suspicions.

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Maybe the colours are the clue, this video was in very nice, green woods, not the monochrome area I was in.

 

[Luckyguy9]

I am not sure how it crashed. I think it hit something but I can't understand why. I don't think it hit the light pole, it was between me and where the drone should have been. The issue is, I had my back. I did not see where it went and I did not record it. I wish I had.

I have been flying for 5 years. I never used anything with active tracking or obstacle avoidance, always flying on manual mode and I have never crashed. I know to avoid power lines and twigs. I trusted the obstacle avoidance and active track. I was playing around with it.

From your description it does seem it crashed into a light post, but wouldn't that be something it should know to avoid? Having said that, the greatest mystery for me is why it circled back behind me if I clearly set it to follow me from the southwest, as I put in the pictures. It should have stayed well clear of both the lamp posts and the trees.

In conclusion, my greatest question is why it crashed. Why did it go where it was not told to or not supposed to. And why did the obstacle avoidance not avoid the crash?

In your photo, those trees have no leaves on them and the drone has a hard time seeing just thin branches with no leaves. It may not be the color it may be the volume the fact that the leaves are a lot busier than thin branches.

 

[aeciolemos]

In your photo, those trees have no leaves on them and the drone has a hard time seeing just thin branches with no leaves

That might be it. I guess I should stay clear of leafless trees and monochrome scenes, as Meta4 showed in the manual.

I still don't understand why it went near those trees. It should have stayed to the left.

 

[Luckyguy9]

That might be it. I guess I should stay clear of leafless trees and monochrome scenes, as Meta4 showed in the manual.

I still don't understand why it went near those trees. It should have stayed to the left.

What was the damage to the drone?