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Crashed my Mini, Need Help Analyzing Flight Data

icecoldgin

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I was out on a late afternoon flight and horror of horrors, the Mini crashed.

Last message I saw on the Fly App was "motor unable to rotate...." (EDITED AFTER REVIEWING FLIGHT PROFILE) and saw the video on my phone of the Mini out of control then coming to a rest among what I could discern are tall grasses.

I was in Sport Mode at that time as it was a bit windy and actually on the way home and descending when this happened.

I am attaching the flight record for help from the kind expert souls here in analyzing the data and letting me know what happened. It is still under warranty so if this is, ehem "not pilot error", there is a chance I can make a claim.

Good news is that it is just nearby, about 800 meters away only from the home point. Bad news is I tried retrieving it this afternoon but the grass was too long and it was getting dark

Will try again to rescue it tomorrow. Hopefully, there will still be enough battery for the drone to flash and beep.

Since the area was very grassy, best case scenario is that the Mini is not too damaged and still a-ok

Worse case scenario is that it is a total loss.

Alternative best case scenario is to use this as a reason to get the Mini 2 or Mavic Air 2, hehehehe. But I digress ;)
 

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  • DJIFlightRecord_2020-11-18_[16-42-32].txt
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icecoldgin

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whilst waiting for analysis try replaying the flight in the "me" section on the front page of the app, you may see your "motor overload...." message etc.
Got it. Replayed the flight and here are some details:

Battery - 51% 10'27"
Alert: "Motor unable to rotate. Check for objects blocking motor or contact DJI Support for assistance"
Height: 167 meters
Distance: 781 meters
S Mode
In Flight
GPS satellites - 16

Last messages were:
"Max power l...ith caution" then "RC not conn ... obile device"
 
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msinger

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Last message I saw on the Fly App was "motor unable to rotate...."
I don't see this message in your flight log, but it does show a motor was blocked at 10m 47s into your flight.

1605698581227.png
 

msinger

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Was it a bird strike? Or some debris being blown towards the Mini?
Both possibilities. You should go retrieve your drone so you can see if there is any evidence of what might have caused it.
 
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Meta4

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I was out on a late afternoon flight and horror of horrors, the Mini crashed.

Last message I saw on the Fly App was "motor unable to rotate...." (EDITED AFTER REVIEWING FLIGHT PROFILE) and saw the video on my phone of the Mini out of control then coming to a rest among what I could discern are tall grasses.

I was in Sport Mode at that time as it was a bit windy and actually on the way home and descending when this happened.

I am attaching the flight record for help from the kind expert souls here in analyzing the data and letting me know what happened. It is still under warranty so if this is, ehem "not pilot error", there is a chance I can make a claim.

Good news is that it is just nearby, about 800 meters away only from the home point. Bad news is I tried retrieving it this afternoon but the grass was too long and it was getting dark

Will try again to rescue it tomorrow. Hopefully, there will still be enough battery for the drone to flash and beep.

Since the area was very grassy, best case scenario is that the Mini is not too damaged and still a-ok

Worse case scenario is that it is a total loss.

Alternative best case scenario is to use this as a reason to get the Mini 2 or Mavic Air 2, hehehehe. But I digress ;)
Your flight data looks like this:

You flew the Mini out 2800 ft, took it up to 640 ft.
At 10:37.3 you started bringing it down with full stick in Sport Mode.
At 10:47 (558 ft up), something goes wrong and the Mini starts spinning anti-clockwise.
The spinning speeds up and the descent speed increases from 3 m/s (normal max descent speed) to 9 m/s and the Mini is tumbling.

The data stops at 11:02.3 (146 ft up).

As power stayed on for most of the fall, it appears that the incident was due to either the loss of a motor or a prop.

The wreckage should be fairly close to 14.19074 121.07110
 
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icecoldgin

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Both possibilities. You should go retrieve your drone so you can see if there is any evidence of what might have caused it.
Operation Rescue Drone will be launched tomorrow.

Hopefully, the grasses cushioned the Mini's fall and it survived.

By the way, will the drone still have battery power for it to flash and beep when I press the "Find My Drone" button?

I have not looked into this but does the Mini automatically shut down if it is not flying or moving after a certain period of time?
 

msinger

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By the way, will the drone still have battery power for it to flash and beep when I press the "Find My Drone" button?
No chance.

I have not looked into this but does the Mini automatically shut down if it is not flying or moving after a certain period of time?
No. But, it will shut down when the battery is depleted.
 

icecoldgin

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Your flight data looks like this:

You flew the Mini out 2800 ft, took it up to 640 ft.
At 10:37.3 you started bringing it down with full stick in Sport Mode.
At 10:47 (558 ft up), something goes wrong and the Mini starts spinning anti-clockwise.
The spinning speeds up and the descent speed increases from 3 m/s (normal max descent speed) to 9 m/s and the Mini is tumbling.

The data stops at 11:02.3 (146 ft up).

As power stayed on for most of the fall, it appears that the incident was due to either the loss of a motor or a prop.

The wreckage should be fairly close to 14.19074 121.07110
Thanks for this analysis.

Loss of prop is another possibility.

Hmm, if this is the case, I could make a warranty claim since I have not changed the props since I flew this.

Guess I will find out when I retrieve the drone tomorrow.
 

msinger

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I could make a warranty claim since I have not changed the props since I flew this
Perhaps, but I don't know if DJI would be too quick to cover a lost prop issue. If you don't protect the props while the drone is in storage and/or don't inspect them pre-flight, you really cannot be sure the props are in good condition and/or properly secured.

The data in your log doesn't indicate the drone lost a prop. I guess it'll all make more sense once you find the drone.
 
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Meta4

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Was it a bird strike? Or some debris being blown towards the Mini?
The pitch and roll data didn't show any sudden drastic changes, so a birdstrike is unlikely.
Blowing debris sounds even more unlikely.

Loss of a motor = loss of the thrust from a motor, rather than physically losing a motor.
 
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icecoldgin

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The pitch and roll data didn't show any sudden drastic changes, so a birdstrike is unlikely.
Blowing debris sounds even more unlikely.

Loss of a motor = loss of the thrust from a motor, rather than physically losing a motor.
Thanks for this analysis.

If this is related to the motor, this could help in a warranty claim.
 

icecoldgin

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Perhaps, but I don't know if DJI would be too quick to cover a lost prop issue. If you don't protect the props while the drone is in storage and/or don't inspect them pre-flight, you really cannot be sure the props are in good condition and/or properly secured.

The data in your log doesn't indicate the drone lost a prop. I guess it'll all make more sense once you find the drone.
Thanks for this analysis.

I guess we will know when I retrieve the drone.

So far with your analysis and that of Meta4, I am getting more clarity on what happened Thumbswayup
 

slup

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... I guess we will know when I retrieve the drone.
The log you attached in your first post is paired with another log ... a .DAT log, also stored in the mobile device you flew with. The mobile device DAT log contains all motor data, with access to that it's usually fairly easy to conclude if it's a prop or a motor failure.

The correct .DAT log for this flight ends with FLY091.DAT ... go here & read up on how to retrieve it under section 3. --> Mavic Flight Log Retrieval and Analysis Guide

Attach it then in a new post here.
 

PhiliusFoggg

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The correct .DAT log for this flight ends with FLY091.DAT ... section 3. --> Mavic Flight Log Retrieval and Analysis Guide

Attach it then in a new post here.
For the OP the above mentioned DAT log should be in the "MCDatFlightRecords" folder. The "MCDatFlightRecords" folder is in the folder where you found the "DJIFlightRecord_2020-11-18_[16-42-32].txt" file
 

slup

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Got it.

Here it is

Thanks and looking forward to the analysis
Mmm ... this doesn't look like a lost prop or a motor that have been blocked (even though it is indeed a lost thrust incident). Furthermore the AC movements when the failure occurs isn't straight forward pointing to the side with the failure ... so it's not easy to pinpoint the correct side by only looking at the .TXT log which only give leads coming from the movements ... but more regarding that further below in the end.

The side that failed was the right front ...

Here below all motors rpm's, something clearly happens at 645sec into the flight where the right front motor (blue graph) rapidly falls from nearly 9000rpm to 1700rpm ... have placed the sudden up pitch in the graph as a time reference (thin black graph).

(Click on all charts below to make them larger)
1605776908694.png

At the same time the flight controller commands that motor (blue graph) full 100% ... so the drop in rpm shown in above chart isn't what the FC wants at all ...

1605777416455.png

All this says that we are dealing with a motor failure & not a lost prop ... with a lost prop we would have seen a max revving motor on the failing side together with a FC command going high in percentage.

The last thing now in order to say it's a seizing motor is to also having a spiking current on the right front motor ... but we don't find that in this case, the current draw (blue graph) is on par with the other 3 motors?

1605777738155.png

So this starts to smell like an electrical fault out to the right front ...

Checking off the voltage out on the motors reveals a really low voltage there at 645sec compared to the others (blue graph) ... So with this I think that we can conclude that your Mini suffered from a electrical fault out to the right front motor making it drastically slow down & start up the falling "death roll".

1605777884420.png

Then lastly (just as a comment) a bit about why it's somewhat difficult to judge which side that fails just out from the AC movements in this case ... Yaw, Pitch & Roll.

As seen in below chart where I have pinpointed the rpm drop for the right front ... we have just 0,5sec before a pitch change up (black graph) which should mean a lost thrust in the rear. At the same time a roll change to the negative side = left ... which should point to a lost thrust on the left side. The last axis, yaw ... move slightly positive = CW which should mean that a CCW torquing side (either right rear or left front) have been lost. So in the end by just looking at the AC movements you're stuck with conflicting data regarding which side that failed.

The sudden AC movements that happens just before the right front fails originate instead from the pilot maneuvering, releasing the elevator stick (right stick full forward) from full in Sport mode & at the same time keeping max negative throttle (left stick full backwards) for max ascent.

1605778581918.png
 
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icecoldgin

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Wow, what an analysis. It will take me weeks to understand this thoroughly.

Tak so mycket Slup. Much appreciated. Jattebra!

One thing that stuck to my mind is that it was the front right motor that failed.

Could this be caused by the reported design flaw where at sport mode, it has been reported that the propellers would hit the body of the Mini at a certain pitch?

Curiously, I rarely use sport mode and only had to do this at that time due to the constant strong wind warning.
 
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