Hello community!
Today I experienced a big drop in altitude with my mini.
I was testing AC orientation after FW 1.0.4 update, so I did my pre flight check, waited for GPS lock over 10 sats and then did hoover checking the AC was responding correctly.
After this I just flew 100-150 meters away and left controls free, I then noticed how the AC was climbing, I repeated the same and then I noticed how it dropped quite a bit.

Thankfully I was always flying VLOS so  I push left stick up full throttle. Repeated the same twice with same results.
I took off from my backyard (up hill) and flew in to lower terrain, so altitude at take off is 2m but where the drop happened I was maybe 30-40m altitude. Thisis why altitude at some point shows negative numbers.

At 8:50 AC climbs.
At 9:50 AC drops
At 11:54 AC gains altitude and then drops.
At 14:20 AC drops.

Airdata fly log: https://app.airdata.com/share/SRsSvb/GENERALOverview

Phantomhelp fly log: https://www.phantomhelp.com/LogViewer/MGSQI90BHSLFHZK22O9U/

Thanks in advance for any help.

Seems there is a bug that still needs to be addressed. This is why I haven't flown mine until the bug is recognized and fixed. This appeared from what I can tell after the FW 1.0.3 update but from what I can tell hasn't been taken seriously by DJI nor the DJI community on the forums. I quit flying my mini after I saw multiple youtube videos of it and then the forum posts starting appearing. I hope they get it sorted soon.

The Watchman News Posted at 1-2 06:51
Seems there is a bug that still needs to be addressed. This is why I haven't flown mine until the bug is recognized and fixed. This appeared from what I can tell after the FW 1.0.3 update but from what I can tell hasn't been taken seriously by DJI nor the DJI community on the forums. I quit flying my mini after I saw multiple youtube videos of it and then the forum posts starting appearing. I hope they get it sorted soon.

I also noted a few guys saying the mini dropped in altitude but they were flying over snow and cold environments, I thought the two were related, but maybe no.

I hope somebody from DJI can answer, I suppose I should open a support ticket, but if they are gonna make me send it back and this is a known bug,I rather wait.

Both times 8.50 and 9.50 you were traveling backwards 100% and terrain is hilly, so this could explain this, however at 11.54 you were hovering and it appeared craft was lowering by a considerable amount , again at 14.20 there was some stick movements so craft was moving again if this was over hilly terrain altitude will fluctuate.

According to flight log, MM was in Sports mode.   Is problem repeatedable in regular mode?

hallmark007 Posted at 1-2 07:23
Both times 8.50 and 9.50 you were traveling backwards 100% and terrain is hilly, so this could explain this, however at 11.54 you were hovering and it appeared craft was lowering by a considerable amount , again at 14.20 there was some stick movements so craft was moving again if this was over hilly terrain altitude will fluctuate.

Yeah I was literally going away and quickly coming back, some times I left the stick go and noticed the climb or drop, it was at 11.50 when it really dropped, I didnt input anything before to see if it would recover the altitude alone, but it was going so fast down I had to make it ascend.

Just puzzled how the terrain would affect this, in theory it should hoover, how could the AC tell how high it is? Why would the terrain below make it drop that much?

HedgeTrimmer Posted at 1-2 07:33
According to flight log, MM was in Sports mode.   Is problem repeatedable in regular mode?

Correct AC was in Sports mode, I haven´t tried in P mode but I will. The behavior only happened when going full speed forward, then letting sticks go 100%, I wonder if this could be related to IMU and inertia.

Only 10 sats, shouldn't you wait until your have at least 11, this guarantees that you have at least 6 of the same type then.

hallmark007 Posted at 1-2 07:23
Both times 8.50 and 9.50 you were traveling backwards 100% and terrain is hilly, so this could explain this, however at 11.54 you were hovering and it appeared craft was lowering by a considerable amount , again at 14.20 there was some stick movements so craft was moving again if this was over hilly terrain altitude will fluctuate.

Hi, how does terrain affect altitude?

DAFlys Posted at 1-2 07:48
Only 10 sats, shouldn't you wait until your have at least 11, this guarantees that you have at least 6 of the same type then.

Minimum safe is 8, I took off with 10, at 0:20 11 sats.
At 1:45 12 sats. At 1:51 13 sats, I didnt go far until I had 12.
I would expect some drift sideways if it was GPS related but not height.

TDZHDTV Posted at 1-2 07:49
Hi, how does terrain affect altitude?

That´s what I wonder...
The 14:20 drop didn´t have any input from my RC neither.

Hiya,

Interesting to see what happend.

When flying full speed forward stick and change this into full aft stick the IMU has to work hard!

Forward thrust and lift must change from fwd to backward, resulting in a climb of a craft if nothing is done to lower the resulting lift component. The only way for a craft like this is done by reducing RPM of the motors. If processed quickly than no ascend or descent to be seen. The ascend en descend by changing rapidly stick inputs looks normal to me.

Its hard to tell on barometer height data if the amount ascending/descending is 100% accurate, but i normally believe that this sensor is quitte accurate.

At 8m30 in sport start to fly forward with 100% stick, baro height 2.6 meter
AT 8m45 with only 100% forward stick height is now 7.7 meter.  Did it really climb 5 meter??
Releasing stick, from 22 degrees pitch down to 32 degrees up ; little normal climb as decribed before.

Mayby do this again within VPS height range, than whe can see (in the log only) the real height fluctuations.


lower chart is 8m50 ; flying full forward, stop, full backwards
cheers
JJB

InspektorGadjet Posted at 1-2 07:38
Yeah I was literally going away and quickly coming back, some times I left the stick go and noticed the climb or drop, it was at 11.50 when it really dropped, I didnt input anything before to see if it would recover the altitude alone, but it was going so fast down I had to make it ascend.

Just puzzled how the terrain would affect this, in theory it should hoover, how could the AC tell how high it is? Why would the terrain below make it drop that much?

If your measurements are coming from vps which work from 0.5 to 10 metre then flying over hilly terrain will change altitude reading as sensor reads from what is under it .

TDZHDTV Posted at 1-2 07:49
Hi, how does terrain affect altitude?

If your flying 30ft or below vps takes measurements from what it’s flying over so over hilly terrain it will fluctuate.

hallmark007 Posted at 1-2 08:12
If your measurements are coming from vps which work from 5 to 10 metre then flying over hilly terrain will change altitude reading as sensor reads from what is under it .

I thought the displayed altitude was relative to the take off location / home point?  

TDZHDTV Posted at 1-2 08:19
I thought the displayed altitude was relative to the take off location / home point?

Mavic Mini does not show VPS height info in the FlyApp. Only barometric sensor data.

Go App does show both if within VPS height range.

cheers
JJB

Hi. I am sorry for the trouble this has caused. With regards to this concern. I would recommend to please refresh the firmware of the said drone using the DJI Assistant 2 and please calibrate the IMU and the remote controller to isolate the issue. Please keep us posted for further assistance. Thank you.

JJB* Posted at 1-2 08:21
Mavic Mini does not show VPS height info in the FlyApp. Only barometric sensor data.

Go App does show both if withing VPS height range.

I’ve noticed flying into wind the MM climbs steadily, the rate of climb is increased when cycling through the flight modes c - p - s,  would you say this is normal behaviour? Many thanks

JJB* Posted at 1-2 08:12
Hiya,

Interesting to see what happend.

Thanks JJB, yes, I´m guessing here I did some extreme speed movements and that is why.
When I just did the return and go without stopping it really climbed 5 meters.
Have to test in P mode or stopping progressively rather than let go sticks.

TDZHDTV Posted at 1-2 08:19
I thought the displayed altitude was relative to the take off location / home point?

Yes it is that’s barometer or barometric pressure it will measure ATO above 10m VPS measurements from 0.5m to 10m

hallmark007 Posted at 1-2 08:12
If your measurements are coming from vps which work from 5 to 10 metre then flying over hilly terrain will change altitude reading as sensor reads from what is under it .

I ve been experimenting a lot in the same spot, mainly using P mode and C and never experienced this regardless of the hilly terrain, it´s all the same around where I live.

I even flew over a 300m cliff drop and AC hoovered correctly.
Not sure the VPS was taking over since it had plenty GPS and height was over 30m.

TDZHDTV Posted at 1-2 08:27
I’ve noticed flying into wind the MM climbs steadily, the rate of climb is increased when cycling through the flight modes c - p - s,  would you say this is normal behaviour? Many thanks

So speed of AC is affecting the accuracy of the height hoover.

DJI Paladin Posted at 1-2 08:26
Hi. I am sorry for the trouble this has caused. With regards to this concern. I would recommend to please refresh the firmware of the said drone using the DJI Assistant 2 and please calibrate the IMU and the remote controller to isolate the issue. Please keep us posted for further assistance. Thank you.

Thanks @DJI Paladin I will and report back.

InspektorGadjet Posted at 1-2 08:37
Thanks @DJI Paladin I will and report back.

I'm starting to sound like their suggestions aren't I?? ROFL!!!!

Don't know if that's a good thing or not!!!

TDZHDTV Posted at 1-2 08:27
I’ve noticed flying into wind the MM climbs steadily, the rate of climb is increased when cycling through the flight modes c - p - s,  would you say this is normal behaviour? Many thanks

yes, its in the specs of the MM  in sport mode the ascend/descend rate it the highest value

InspektorGadjet Posted at 1-2 08:29
Thanks JJB, yes, I´m guessing here I did some extreme speed movements and that is why.
When I just did the return and go without stopping it really climbed 5 meters.
Have to test in P mode or stopping progressively rather than let go sticks.

uhm, that 5 meter climb is weird or mabyb not so...
If the pressure measuring is affected by the forward speed than its possible ; bit higher airpress in the sensor and this measured higher value means lower altitude thus imu correcting to climb.

JJB* Posted at 1-2 08:46
yes, its in the specs of the MM  in sport mode the ascend/descend rate it the highest value

Sorry, I wasn’t clear, without any ascend up stick movement the AC climbs if I attempt to only fly horizontal full speed into the wind.

InspektorGadjet Posted at 1-2 08:32
I ve been experimenting a lot in the same spot, mainly using P mode and C and never experienced this regardless of the hilly terrain, it´s all the same around where I live.

I even flew over a 300m cliff drop and AC hoovered correctly.

AFAIK baro height is always measured and use for height hold.
Only within VPS sensor range this measuring is used for landing protection.
That`s why you can fly over an object and remain at fly altitude when VPS is indicating  i.e.  4 meter > 2 meters > 4 meters.....  2 meters when over the object.
Only when lower than VPS 0.5 meters the craft will fly up little.

If you fly not MM, and flying low steady altitude you will see baroheight steady indicating and VPS height fluctuating if the distance craft-ground is changing.

TDZHDTV Posted at 1-2 08:51
Sorry, I wasn’t clear, without any ascend up stick movement the AC climbs if I attempt to only fly horizontal full speed into the wind.

oke, see #28

JodyB Posted at 1-2 08:45
I'm starting to sound like their suggestions aren't I?? ROFL!!!!

Don't know if that's a good thing or not!!!

Lol no it makes sense, you are getting naturally DJIfyed
Have to do the whole DJI Assistant thing tonight.

JJB* Posted at 1-2 08:50
uhm, that 5 meter climb is weird or mabyb not so...
If the pressure measuring is affected by the forward speed than its possible ; bit higher airpress in the sensor and this measured higher value means lower altitude thus imu correcting to climb.

I normally fly very soft and cautious, I try to stop gradually too, today was the first time I went full on Sports mode doing quick tests, so probably this was the reason.
Thanks for the input JJB.

InspektorGadjet Posted at 1-2 09:32
I normally fly very soft and cautious, I try to stop gradually too, today was the first time I went full on Sports mode doing quick tests, so probably this was the reason.
Thanks for the input JJB.

I was playing around with sport mode yesterday out by the house. We have a street that is barely used and I was showing the mini to my son-in-law. He asked how fast it would go and I thought a demo would be in order. I had the mini about 3-4 meters altitude and ran it down the street and turned and came back a couple times in sport mode. It did well actually. He was impressed as well. Now he thinks he might want one too.

JodyB Posted at 1-2 09:38
I was playing around with sport mode yesterday out by the house. We have a street that is barely used and I was showing the mini to my son-in-law. He asked how fast it would go and I thought a demo would be in order. I had the mini about 3-4 meters altitude and ran it down the street and turned and came back a couple times in sport mode. It did well actually. He was impressed as well. Now he thinks he might want one too.

Oh dear, not sure if that is good or not lol
Sports mode is great, I used it a few times to return home manually and when birds git dangerously close or even attacking, you can come back very safely and fast.

However momentum an inertia increases so much, it takes a good amount of distance to stop, something to consider while flying near stuff.

I think my drop issue is related to high speed and quick stop, will update all, calibrate and repeat same test tomorrow.

InspektorGadjet Posted at 1-2 09:45
Oh dear, not sure if that is good or not lol
Sports mode is great, I used it a few times to return home manually and when birds git dangerously close or even attacking, you can come back very safely and fast.

Speed does affect stopping distance. I remember the law of physics, an object in motion wants to stay in motion unless influenced by an outside force. Like vehicles, the faster you go the more it takes to stop. Definitely gives credence to objects near by. When I was showing to my son-inl-law, we were standing in the flight path and when I would bring it back I was able to judge the distance and stop about a meter in front of us.

JodyB Posted at 1-2 10:18
Speed does affect stopping distance. I remember the law of physics, an object in motion wants to stay in motion unless influenced by an outside force. Like vehicles, the faster you go the more it takes to stop. Definitely gives credence to objects near by. When I was showing to my son-inl-law, we were standing in the flight path and when I would bring it back I was able to judge the distance and stop about a meter in front of us.

Absolutely, basic law of physics. I also managed to tell distance of near objects and stop accordingly.

Even though DJI Assistant 2 told me everything was correctly updated to latest version, I did refresh the update again just in case... Too late to test out again but I will tomorrow with sun light.

I will perform IMU and Compass calibration as suggested first thing in the morning to see if problem persists or it goes away.

InspektorGadjet Posted at 1-2 10:28
Absolutely, basic law of physics. I also managed to tell distance of near objects and stop accordingly.

Even though DJI Assistant 2 told me everything was correctly updated to latest version, I did refresh the update again just in case... Too late to test out again but I will tomorrow with sun light.

Man, I really hope it fixes this for you!!!! I know you will keep us updated my friend!!

JodyB Posted at 1-2 10:29
Man, I really hope it fixes this for you!!!! I know you will keep us updated my friend!!

I will, I may try to record video of the action, hopefully if the drop happens again it can be recorded.
It was quite obvious and drastic maybe too small for camera to pick it up.

InspektorGadjet Posted at 1-2 09:32
I normally fly very soft and cautious, I try to stop gradually too, today was the first time I went full on Sports mode doing quick tests, so probably this was the reason.
Thanks for the input JJB.

no thanks,   ido fly cautious as well but its fun to see what is possible to do.
Flying full speed forward, up  and than quickturn to fly forward and decscending again....good fun to do  ;-)

cheers
JJB

My mini dropped today too, and it never happened before. I thought wind mustve been the problem, but usually during windy flights drona changes its x y rotation a bit but today it waant like that, so I think it was not the wind that caused it. I was going back to my position at around 20m hight, not more than 50m distance, iflying n P mode and it just dropped like 3-4m down. I thought it was a gonner-it was across water.
I have it on video , gonna post  tomorrow .

JJB* Posted at 1-2 12:32
no thanks,   ido fly cautious as well but its fun to see what is possible to do.
Flying full speed forward, up  and than quickturn to fly forward and decscending again....good fun to do  ;-)

I think we all like to do "tricks" on occasion. They are very much good fun!! Just got to know your limits, but how else to learn them?