In two of my last three flights (May 23, May 1, March 31), I encountered behavior that I had not experienced before. Both times were over water. I have been flying since January 25, 2021 and have 141 flights flying over water almost all of the time. Today, when I took off, I was able to fly to the spot that I wanted to take photos (H17ft D124ft). After about 10 minutes of holding at altitude and taking photos, I began to change altitudes to get different perspectives. When I increased altitude, the drone continued climbing after I released the stick to the neutral position. I noticed that my altitude was -0.3ft even though I am sure that I was higher than 20ft. To stop the ascent, I had to press the stick to the descend position.

The drone started to descend and would not stop even with the stick in the neutral position. I had to press the stick to the ascend position to stop the drop. Although I was able to stabilize the altitude, this happened several times. I landed and then tried to repeat the flight. This time, altitude was at 20ft when I really was at 20ft. This behavior was observed today and on March 31. I can’t remember if it happened on May 1 or not.

At DJI’s recommendation, I calibrated compass and IMU. I went back to the spot where I had the problem today. The drone flew beautifully for the first 7 or so minutes. After that, I saw the altitude reading drop to negative numbers while the drone was flying at 20 or so feet. It started to exhibit the same bad behavior when ascending and descending (although it was better than this morning). The ascending and descending problem seemed to be associated with or was worse over water. But, the altitude was wrong when I was over land.

Remote calibrated.

Flight okay over water May 24.

July 11. Second flight since May. Once again, the drone flew well over water for the first three minutes. Then it would not stop ascending or descending after the control sticks were released. Also, the altitude read out was not changing when the drone was ascending or descending. I had to return to over land. When I landed at home the altitude was reading negative.

I'd like to hear from you regarding this behavior.

It would be interesting to see the log files.  

ririlan Posted at 7-11 08:13
It would be interesting to see the log files.

DJI wants to check out the IMU. So, I'll be sending it back for repair.

Hi,

If you like post your log(s) on here for this issue....

Use this link > https://www.phantomhelp.com/LogViewer/Upload/
Post the upload link(s) on here.

Mayby logs will explain what happend, and you can compare this with the DJI findings....

cheers
JJB

JJB* Posted at 7-11 08:55
Hi,

If you like post your log(s) on here for this issue....

https://www.phantomhelp.com/LogViewer/4CYKC3QPBLBTBSAFWIZ7
https://www.phantomhelp.com/LogViewer/4EXDE1IBCJ3FDR22YGRU

Your drone has two different sensors that measure height.
One supplies the height relative to the launch point and comes from a barometric sensor.
This is the height you see on your screen and the sensor can show some drift over the time of a flight.

The second sensor is part of the VPS sensors.
It shows the height above what is below the drone and has a limited range, but does not drift over time.
The data from the VPS isn't shown onscreen, but it is shown in the recorded flight data.

Your barometric sensor was obviously showing drift that increased during the flight - showing -20 ft when you were well clear of the water.
But comparison of the heights in the data and your joystick inputs, indicates that the drone was holding altitude normally.

Then it would not stop ascending or descending after the control sticks were released. Also, the altitude read out was not changing when the drone was ascending or descending. I had to return to over land. When I landed at home the altitude was reading negative.
I can't find anywhere in the data for the 2nd flight where the drone continued to climb or descend after you released the throttle.
It seems to hold altitude well and respond normally to the controls.


Perhaps you were confused by the false height given by the barometric sensor?
Recalibrate the IMU and do some testing somewhere you can see the drone and how it responds to your control inputs.

Hello there. I am sorry for the trouble this has caused and thank you for reaching out.  Just a reminder that when flying above the water, the vision positioning function will turn off automatically and only the GPS and barometer are used for positioning, if affected by the accuracy range, and an accident might happen. In addition I will also post a DJI Forum thread below on How to Fly Safely Over Water. Thank you.

https://forum.dji.com/forum.php?mod=viewthread&tid=181878

DJI Stephen Posted at 7-11 19:02
Hello there. I am sorry for the trouble this has caused and thank you for reaching out.  Just a reminder that when flying above the water, the vision positioning function will turn off automatically and only the GPS and barometer are used for positioning, if affected by the accuracy range, and an accident might happen. In addition I will also post a DJI Forum thread below on How to Fly Safely Over Water. Thank you.

https://forum.dji.com/forum.php?mod=viewthread&tid=181878

Just a reminder that when flying above the water, the vision positioning function will turn off automatically
That's completely irrelevant to altitude holding, which is what the OP is asking about.

DJI Stephen Posted at 7-11 19:02
Hello there. I am sorry for the trouble this has caused and thank you for reaching out.  Just a reminder that when flying above the water, the vision positioning function will turn off automatically and only the GPS and barometer are used for positioning, if affected by the accuracy range, and an accident might happen. In addition I will also post a DJI Forum thread below on How to Fly Safely Over Water. Thank you.

https://forum.dji.com/forum.php?mod=viewthread&tid=181878

Hi Stephen,

And again you post this outdated link!!  why ?

FlyApp drones cannot disable the VPS bottem sensor!!

And the vision positioning is not turned off automatically flying over water!
And what do you mean with "...affected by the accuranct range, an accident might happen" ?? It is so wrong!

I fly many times low over water, VPS bottom sensor does sense alway the correct height.Only when flying slow or hovering low over streaming water the VPS downward sensor gets sometimes "confused"....
Well, just my experience flying many many flights low over water.
And, analyzing logs, you can see that the vision is not used for positioning when the GPS signals are oke. (see the manuals as well ....)

Best for DJI is to change the autolanding protection such that it will automatically turns off with some speed in any direction! This has caused many wet drones....

see https://forum.dji.com/forum.php?mod=viewthread&tid=268606 #11

Cheers
JJB

fans04398259 Posted at 7-11 13:00
https://www.phantomhelp.com/LogViewer/4CYKC3QPBLBTBSAFWIZ7
https://www.phantomhelp.com/LogViewer/4EXDE1IBCJ3FDR22YGRU

Hi,

Had a look at your 2 logs too.

In both flights i do not see uncontrolled ascent and/or descent.
See my charts of your data.

In both charts the upper grapgh > blue line = baro height, green line = bottom sensor height
Where the blue|green lines are coloured red = descent with no RC input, yellow = ascent with no RC input.
You can check the RC up|down inputs to the height changes yourself.

Your lines are normal, even coloured red/yellow as height need some time to  stabilize after releasing input to zero.  All red/yellow parts are only few cm so absolutely normal.

Hope you did not sent your drone already to DJI....as imo nothing wrong with your drone.
Why the Barometric height in both flights went into zero...no idea but few meters into plus or negative is 'normal' if the takeoff spot = landing spot ofcourse.
Check this in another flight ; takeoff - go to 400 feet - land ; check the baro height indication.


cheers
JJB

Thanks for all of the comments. If you look at 3min 28s to 3 min 35 sec in:

https://www.phantomhelp.com/LogViewer/4EXDE1IBCJ3FDR22YGRU

You will see me push the left joy stick down then quickly up. I did this to counter uncontrolled ascent or descent. I immediately aborted and flew back over land as I knew from experience that the behavior would continue.

fans04398259 Posted at 7-14 04:27
Thanks for all of the comments. If you look at 3min 28s to 3 min 35 sec in:

https://www.phantomhelp.com/LogViewer/4EXDE1IBCJ3FDR22YGRU

You will see me push the left joy stick down then quickly up. I did this to counter uncontrolled ascent or descent.
I see you had the throttle down, then left it centred for a second and then push up.
But there's no uncommanded descent in the second before you pushed the throttle up.
In fact the drone actually rose 1.3 ft.

I immediately aborted and flew back over land as I knew from experience that the behavior would continue.
There's nothing in that data from this flight to support what you are saying.
How about flying again, putting the drone 100 ft up and showing what happens when you descend for a bit and then centre the left stick.

Labroides Posted at 7-14 05:19
You will see me push the left joy stick down then quickly up. I did this to counter uncontrolled ascent or descent.
I see you had the throttle down, then left it centred for a second and then push up.
But there's no uncommanded descent in the second before you pushed the throttle up.

Thanks. I think that I need to have a screen recording which would provide direct info on the ascent or decent independent of the altitude sensors.

fans04398259 Posted at 7-14 04:27
Thanks for all of the comments. If you look at 3min 28s to 3 min 35 sec in:

https://www.phantomhelp.com/LogViewer/4EXDE1IBCJ3FDR22YGRU

Hi,

Had a another check on your flight, to find evidence of your uncontrolled descent.
Eye ball mark 1 vision is often correct watching drone close by  ;-)
See my chart of your data.

Interesting, as the baro height and bottom sensor height does not show any descent at all !, The vertical speed indicates 0.5 meters down speed, this for approx 1.5 second.
So this data match with descend you did notice and the reason you pushed your drone UP.
But this after pushing your drone down before....

btw  i ALWAYS fly with screen recording on,  very usefull in analyzing data. (plus to see messages wich dissapear quickly while watching drone not the screen)

cheers
JJB

fans04398259 Posted at 7-14 05:37
Thanks. I think that I need to have a screen recording which would provide direct info on the ascent or decent independent of the altitude sensors.

Do you have a particular reason to distrust the altitude sensing of the drone?
The barometric sensor is usually very reliable.

I have resolved the problem. DJI asked for the drone to be returned for repair. I did so and they chose to replace it. I took the new drone out for a flight this morning and it performed flawlessly. What a difference between this new drone and my old one. The old one gave me heart palpatations when I flew it over water. Here is a photo from this morning.

Enjoy your new drone and keep posting those fantastic pictures.