Mavic mini moved alone without stick input

[fabri01]

Hi, yesterday during my flight I was above the sea and the MM started to fly backward at high speed alone. Fortunately i was able to recover it by using sport mode, but it was difficult to control. I didn’t receive any warning or message in the dji fly app. Now I am a little bit scared to fly. What might have happened? (Maybe wind, vps failure, need to replace propellerls?)
I attach here the txt and dat file. 14 minutes and 12 seconds
Dat file:

2022-08-09_09-49-40_FLY009.DAT

drive.google.com

Thanks

 

[GFields]

How high were the winds?

 

[fabri01]

How high were the winds?

Not so much, but the strange things is that I didn’t receive any warning in the app

 

[Yorkshire_Pud]

your log on Phantomhelp DJI Flight Log Viewer - PhantomHelp.com

Is the DAT file on a page that is public? It's asking me to sign in to google.

 

[fiberdude]

Not so much, but the strange things is that I didn’t receive any warning in the app

Nice island you are hanging out on. The home point on the beach seems to be shielded from wind, but when the drone was vertically above the highway (around 100m in altitude, 60% battery, see below), the wind could be strong. MM is known to be weak against wind in the normal mode.

It is probably a good idea to use a heavier drone (such as Mavic 2 Pro) for flights on a beach just below a cliff.

 

[Meta4]

What might have happened? (Maybe wind, vps failure, need to replace propellerls?)

None of those could cause the incident that's shown in the flight data.
It's a strange one that I've never seen before.
I'd suspect the IMU is involved, but can't see how it's had this effect.
Perhaps @slup or @sar104 might have an idea about it.

The speed indicated in the flight data was erratic, rapidly increasing and decreasing much quicker than can happen in normal flight.
At 14:13.6 the indicated speed jumped from 3 mph to 12.7 mph in 0.1 sec and things started going crazy with the speed jumping up and down from then until the end of the flight.

The data shows that the problem started earlier but the speeds were slower, so not so noticeable.

 

[FLDave]

Control stick movement seems a bit erratic as does the changes between GPS, Sport, and tripod modes.
I think it also suggests winds blowing off short. Your best information on wind is what you were feeling on shore, with a velocity number. When unsure about wind, get a handheld anemometer to measure wind velocity. Next, make sure you understand how terrain can impact on wind at higher elevations.
Control over water and uneven terrain needs special visual control. When in doubt get the drone back and land immediately.

 

[Meta4]

I think it also suggests winds blowing off short. Your best information on wind is what you were feeling on shore, with a velocity number. When unsure about wind, get a handheld anemometer to measure wind velocity.

There's nothing in this incident that's remotely like the effect of wind on a drone.
The speed was rapidly increasing and decreasing at a rate that's impossible in normal flying.

Here's a small sample of the speed variations.

Drones don't just jump from 3.4 mph to 17 mph in 1/10th of a second.
Clearly the speed readings can't be completely true and the Flight Controller must have been getting crazy speed data and responding to that.

 

[FLDave]

There's nothing in this incident that's remotely like the effect of wind on a drone.
The speed was rapidly increasing and decreasing at a rate that's impossible in normal flying.

Here's a small sample of the speed variations.

Drones don't just jump from 3.4 mph to 17 mph in 1/10th of a second.
Clearly the speed readings can't be completely true and the Flight Controller must have been getting crazy speed data and responding to that.

I take it, then that your conclusion is that wind and wind shear had no impact on flight controls for this flight?

 

[Meta4]

I take it, then that your conclusion is that wind and wind shear had no impact on flight controls for this flight?

There's nothing in this incident that's remotely like the effect of wind on a drone.
Nothing at all.

 

[fabri01]

There's nothing in this incident that's remotely like the effect of wind on a drone.
Nothing at all.

So what was the problem?

 

[fabri01]

I have read other threads and I find out this thing:

Mini 2 gimbal pointed straight down -- maximum speed reduced?

It seems like the maximum forward speed of the drone (in normal mode) decreases markedly when the gimbal is pointed straight down. Is this just me imagining things or is this a real phenomenon? If it's real, is it due to wind resistance or something? (That'd really be something such a small...

mavicpilots.com

If I remember correctly I was pointing the gimbal straight down in that moment, but as written in the drone manual, If the drone detect high wind it should remove the speed limitation. But during that flight I didn’t get any wind warning.
Moreover, I tried to analyze the dat file and I discovered that the wind detection in that moment seems to be stuck. So maybe this might be the problem?

Do you recommend me to calibrate the IMU?

 

[Meta4]

So what was the problem?

It's discussed in earlier posts.

If I remember correctly I was pointing the gimbal straight down in that moment

Your gimbal pitch was varying between 70° and 84° when things were acting up

I didn’t get any wind warning.

The flight data shows wind was very light.
This is confirmed by pitch and roll data.
Wind had nothing to do with the incident !!

Do you recommend me to calibrate the IMU?

Perhaps it would help ... do some test flying afterwards to confirm that the drone is flying properly.

 

[BudWalker]

There's nothing in this incident that's remotely like the effect of wind on a drone.
The speed was rapidly increasing and decreasing at a rate that's impossible in normal flying.

Here's a small sample of the speed variations.

Drones don't just jump from 3.4 mph to 17 mph in 1/10th of a second.
Clearly the speed readings can't be completely true and the Flight Controller must have been getting crazy speed data and responding to that.

That's due to a known problem caused by aliasing. Better results can be obtained from time differentiating Lat/Long data. In CsvView this computation is provided as ImuCalcs:velH. Here is the interval you referenced.


I've only looked at this briefly but, so far, I'm suspecting that the erratic flight was wind related.

 

[BudWalker]

Hi, yesterday during my flight I was above the sea and the MM started to fly backward at high speed alone. Fortunately i was able to recover it by using sport mode, but it was difficult to control. I didn’t receive any warning or message in the dji fly app. Now I am a little bit scared to fly. What might have happened? (Maybe wind, vps failure, need to replace propellerls?)
I attach here the txt and dat file. 14 minutes and 12 seconds
Dat file:

2022-08-09_09-49-40_FLY009.DAT

drive.google.com

Thanks

I found one interval in the flight that matches your description (there may be other matching intervals). At 854 full positive elevator was applied while in P-GPS mode. In response the MM pitched down to -11°. Then at 856 the MM went to Sport mode and the MM pitched down to -27°.



Yet the MM was moving backwards in this interval


I think this has to be caused by the wind

 

[slup]

...At 854 full positive elevator was applied while in P-GPS mode. In response the MM pitched down to -11°. Then at 856 the MM went to Sport mode and the MM pitched down to -27°.

Still haven't a computer so can't dig in myself ... but a pitch to only -11 degrees in P-mode with full elevator stick caught my eye.

In P-mode the MM should be able to achieve a tilt of -20 degrees according to the specs ... is this again a case where the rear props is slightly flattened & can't tilt the AC properly forward but not yet have developed to a full uncommanded descent?

What was the RPM's on the motors during that interval ... close to max?

I think this has to be caused by the wind

If this was a case of flattened props the wind is a cause ... but it's not the root cause, if the AC can't tilt according to spec it will "blow away" even in very light winds.

 

[Meta4]

I think this has to be caused by the wind

Can you explain what causes the crazy indicated speed changes?

 

[BudWalker]

Still haven't a computer so can't dig in myself ... but a pitch to only -11 degrees in P-mode with full elevator stick caught my eye.

In P-mode the MM should be able to achieve a tilt of -20 degrees according to the specs ... is this again a case where the rear props is slightly flattened & can't tilt the AC properly forward but not yet have developed to a full uncommanded descent?

What was the RPM's on the motors during that interval ... close to max?


If this was a case of flattened props the wind is a cause ... but it's not the root cause, if the AC can't tilt according to spec it will "blow away" even in very light winds.

You're right, -11° pitch is too shallow for P-GPS mode. I don't have access to the .DAT. The GoogleDrive link posted in post #1 requires that @fabri01 grant access to the .DAT.

I had to go back and take a look at the uncommanded descent issue. Your supposition that this may have been a partial UD seems plausible to me. I didn't see any indications in the height data to indicate UD. The MM was being blown towards the HP - maybe the FC was smart enough to allocate thrust to maintaining altitude instead of allocating it to returning to home.

@fabri01 I would be interested in seeing the .DAT. It would show how thrust was being allocated. Some may find this post relevant.
Mavic Mini uncommanded descent tests

 

[Yorkshire_Pud]

I LOVE how deep a seemingly simple problem can lead. Just shows how complicated these things are yet normally so seemingly simple.

 

[fabri01]

You're right, -11° pitch is too shallow for P-GPS mode. I don't have access to the .DAT. The GoogleDrive link posted in post #1 requires that @fabri01 grant access to the .DAT.

I had to go back and take a look at the uncommanded descent issue. Your supposition that this may have been a partial UD seems plausible to me. I didn't see any indications in the height data to indicate UD. The MM was being blown towards the HP - maybe the FC was smart enough to allocate thrust to maintaining altitude instead of allocating it to returning to home.

@fabri01 I would be interested in seeing the .DAT. It would show how thrust was being allocated. Some may find this post relevant.
Mavic Mini uncommanded descent tests

I have made the link public