I have been flying my Mavic Mini for about half a year with no problems. Always did what I commanded from the controller; very stable and predictable... Until today.
I started drone to shoot my friends on motorcycles. After I change the mode for speed and was looking for spot Mavic Mini rapidly accelerated toward ground, hit it, bounce back at altitude and returned to work properly. I have never experienced such a strange behavior. Shouldn't proximity sensors stop Mini to hit a ground ? I attached flight logs. At some point altitude reads negative values. Isnt it faulty reading?

Hi Kedriik,

Had a look at your flight, see the chart.

MM is not the best drone to hold height with RC inputs (forward/aft, up/dn inputs)
In your flight, flying at low altitude your input was stick down, than both input to zero.
MM dropped in height (as commanded) but did not react fast enought to stop the descend.

In my experience this happens to a MM, normally flying higher you would not notice this in flight, i mean at 100 meters away and 50 meters height droping 2 meter is not seen (well, not by me)

a MA2 can do this much better (height stabilisation is very good), a MM will vary in height with (rapid) RC inputs.

I cannot say if your MM performed worse than other MM, so its a question for DJI i think.

Neagtive height values are normal to be seen; your takeoff height is the reference zero height. The barometric sensor will indicate the height, i.e.  start a flight, climb to 100 meters and land again where you started the flight. Zero is the value to be expected, but height value vary between 1-2 meter up (positive value) or down (negative value)

In the log you see the VPS height sensor value, this actually measure the height between drone<>surface below craft.In the chart see that the VPS height is indeed zero at 'touch down".

cheers
JJB

JJB* Posted at 9-13 01:12
Hi Kedriik,

Had a look at your flight, see the chart.

Hey and thank you very much for analysing my flight logs.
First of all I did not command descend when this happened. It was hovering while I was thinking how to make a shot.
The second thing is that if I'd commanded descend till the ground shouldn't it dispatch landing procedure?

Kedriik Posted at 9-13 01:56
Hey and thank you very much for analysing my flight logs.
First of all I did not command descend when this happened. It was hovering while I was thinking how to make a shot.
The second thing is that if I'd commanded descend till the ground shouldn't it dispatch landing procedure?

Hi,

The log shows that you commanded stick down for 0.7 of a second, craft followed this and descended, see the vertical speed values.It just did not stopped the descend quick enough.

For the automatic autolanding few conditions have to be met
1) VPS height of approx 0.5 meter [ your craft did fly at 3 meter VPS height)
2) short while 100% stick down [ your input less than 100%]

cheers
JJB

JJB* Posted at 9-13 02:40
Hi,

The log shows that you commanded stick down for 0.7 of a second, craft followed this and descended, see the vertical speed values.It just did not stopped the descend quick enough.

I see, thanks for information.
However this is my point, Iam pretty sure that I did not command descend. From where this command came from? Was this interference ? The drone was under electric cables but signal strength was strong. No other drones were flying near by.

Kedriik Posted at 9-13 02:58
I see, thanks for information.
However this is my point, Iam pretty sure that I did not command descend. From where this command came from? Was this interference ? The drone was under electric cables but signal strength was strong. No other drones were flying near by.

Mayby accindentally you move the down stick for short moment, not likely that any other reason would lower your MM.

If any signal was disturbed by elec cables or so...(i fly along elec cables and no interference ect)
than craft would moved etc  but ofcourse no RC stick input in the log present.

Mayby more info in the DAT file (FLY031.DAT), also on your mobile device (in the MCDatFlightRecords map)If you like put a cloud link to that file on here.

cheers
JJB

If it was solid ground it touched down on. You should open a ticket and have DJI check your log. The IR sensors next to the down camera should stop the descent at about knee height (50cm).

Hello there Kedriik. I am sorry for the trouble this has caused and thank you for reaching out. Since there was a crash that happened before on your DJI Mavic Mini and you are now experiencing this issue. It would be best to contact our DJI support team at https://www.dji.com/support for further assessment on the said drone . We have a team that will do there best to analyze and give out the best resolution for this issue. Again. I am sorry for this trouble and thank you for your understanding.

DJI Stephen Posted at 9-13 21:44
Hello there Kedriik. I am sorry for the trouble this has caused and thank you for reaching out. Since there was a crash that happened before on your DJI Mavic Mini and you are now experiencing this issue. It would be best to contact our DJI support team at https://www.dji.com/support for further assessment on the said drone . We have a team that will do there best to analyze and give out the best resolution for this issue. Again. I am sorry for this trouble and thank you for your understanding.

Hey,
What crash? I have never crashed it before. How do you know if it was crashed ?

Guorium Posted at 9-13 06:26
If it was solid ground it touched down on. You should open a ticket and have DJI check your log. The IR sensors next to the down camera should stop the descent at about knee height (50cm).

True, but not when rate of descend down is 2.4 m/s.

If you hover in sport mode at height, fully down (3 m/s down), than in reach of the VPS sensor you will see that the rate of descend is reduced to zero (at 0.5 meter vps height), this while you input 100% stick down all the time.

In this flight shortly pushing down at 3 meter fly height the result was more than normal rate of descend. Curious about the DAT, it looks like a height controlling error.

cheers
JJB

JJB* Posted at 9-14 00:04
True, but not when rate of descend down is 2.4 m/s.

If you hover in sport mode at height, fully down (3 m/s down), than in reach of the VPS sensor you will see that the rate of descend is reduced to zero (at 0.5 meter vps height), this while you input 100% stick down all the time.

Either way the sensor failed and the OP can get a replacement unit or at least a repair.

Guorium Posted at 9-14 06:34
Either way the sensor failed and the OP can get a replacement unit or at least a repair.

I just did test on my own good working MM.

Fly at 0,5 meter forward up a slope....only with low low speed (< 0.3 m/s) my MM started to climb up the slope.
If i fly faster the up steer command is to slow, so MM flys into the slope.

So i am not convinced that this sensor has the capability to steer up fast if drone descend rather fast.

cheers
JJB

JJB* Posted at 9-14 07:20
I just did test on my own good working MM.

Fly at 0,5 meter forward up a slope....only with low low speed (< 0.3 m/s) my MM started to climb up the slope.

Of course it take a while to react but the OP was not flying into a slope was he? I think he touched down on flat ground

Guorium Posted at 9-14 17:11
Of course it take a while to react but the OP was not flying into a slope was he? I think he touched down on flat ground

yes, i know    but imo this sensor is not for stopping a fast descend as in this OP flight.
My test just to prove that it does not react quick enough.

sensor doesnt know if the surface below is a slope or solid ground, the change (surfase closing in)  in signal will give a steer-up command  but really slow....

cheers
JJB

I have had the exact same problem on multiple times, and its not me crashing inti the ground, all of a sudden at 30m or higher, the drone starts decending at a rate far faster than normal, and I try control it up,  but it doesnt stop, it will still go sideways, while decending, but not up, until it crashes and if the ground is flat, it will bounce back up and then fly normally like nothing happened, but there was no obedience while it was decending like crazy