Auto-landing when descending below take-off altitude.

[ManBearPig1989]

Hey all, currently getting an issue where my drone will auto-land when taking off from a lookout and then trying to descend down into a valley with a waterfall. Whenever I try to descend below the take-off altitude (i.e; anywhere below 0m height), my drone goes into auto-landing mode and the descent occurs extremely slowly. I don't remember it doing it anywhere else and the only times this has happened has been when recording big waterfalls. Does anyone happen to know why this could be? Any feedback on this would be hugely appreciated.

 

[Meta4]

Whenever I try to descend below the take-off altitude (i.e; anywhere below 0m height), my drone goes into auto-landing mode and the descent occurs extremely slowly.

Negative height makes no difference to the drone.
It's not programmed to descend on going negative.
Perhaps your recorded flight data could help solve the mystery.

 

[Deleted member 94047]

Are you by chance launching from outside of but entering into a restricted zone in the process? That would explain it.

 

[msinger]

@ManBearPig1989, it sounds like forced landing mode is being enabled due to holding the throttle in the full down position while the downward sensors are detecting something near the bottom of the aircraft. If you upload one of your TXT flight logs here and post the link back here, I can confirm whether or not that's happening.

 

[ManBearPig1989]

@ManBearPig1989, it sounds like forced landing mode is being enabled due to holding the throttle in the full down position while the downward sensors are detecting something near the bottom of the aircraft. If you upload one of your TXT flight logs here and post the link back here, I can confirm whether or not that's happening.

Not sure how I go about doing that... My only hypothesis is that DJI applies a countrywide restriction on flying in national parks rather than by the state laws. As it only seems to happen in the national parks - which, as far as I understand is allowed to be flown in in my state of Queensland but none of the other states.
Nevermind, found the flight log:

 

[Meta4]

Not sure how I go about doing that... My only hypothesis is that DJI applies a countrywide restriction on flying in national parks rather than by the state laws. As it only seems to happen in the national parks - which, as far as I understand is allowed to be flown in in my state of Queensland but none of the other states.
Nevermind, found the flight log:

Here's what your flight data looks like: DJI Flight Log Viewer - PhantomHelp.com
Your Forced Landing began at 2:16.5 when the drone was 17 feet higher than the launch point.
So you can scrub your idea about negative height being a factor.

Your suggestion of a DJI enforced ban on flying in national parks isn't correct either.
But if it was you wouldn't have been able to launch.

Do you have a gimbal guard etc that's blocking your downward facing sensors?
Because the VPS data shows that your drone thought it had landed almost all of the flight.

 

[Air_Joe]

Could it be the drone sensor is confused by the fast moving water below ?

Have u tried a short flight above land?

 

[Meta4]

Could it be the drone sensor is confused by the fast moving water below ?

Have u tried a short flight above land?

As in post #6, it was because something is blocking his VPS sensors.

 

[sar104]

The problem is that the aircraft bottom sensor is not working - it continuously reads zero height (red trace). As a result, every time you apply full down throttle (black trace) the aircraft enters forced landing mode (green trace):

 

[msinger]

The problem is that the aircraft bottom sensor is not working

That -- or some type of 3rd party accessory is installed near the sensors on the bottom of the aircraft.

 

[sar104]

That -- or some type of 3rd party accessory is installed near the sensors on the bottom of the aircraft.

Yes - that could cause the problem.

 

[msinger]

@ManBearPig1989, did you have any 3rd party accessories installed near the bottom of your Mavic?

 

[ManBearPig1989]

Here's what your flight data looks like: DJI Flight Log Viewer - PhantomHelp.com
Your Forced Landing began at 2:16.5 when the drone was 17 feet higher than the launch point.
So you can scrub your idea about negative height being a factor.

Your suggestion of a DJI enforced ban on flying in national parks isn't correct either.
But if it was you wouldn't have been able to launch.

Do you have a gimbal guard etc that's blocking your downward facing sensors?
Because the VPS data shows that your drone thought it had landed almost all of the flight.

No, definitely can't see any sensor obstruction, and I never take off with the gimbal on. As far as I can tell, the downward sensors were completely clear. This doesn't happen at any other location hence why I thought it might be due to the area. Are you absolutely certain that it's not due to the flight being listed in a national Park? That seems to be the only common factor.
Edit: just read the other replies given I just woke up. No accessories whatsoever have been installed on the drone. This doesn't happen anywhere else when flying and descending - Only over the two waterfalls listed in the national Park regions.

 

[msinger]

Are you absolutely certain that it's not due to the flight being listed in a national Park?

I am. Forced Landing mode was being initiated each time you had the throttle in the full down position while the downward sensors were detecting an obstacle close to the bottom of the aircraft (as it's designed to work).

You either have a problem with your downward sensors or you had some type of 3rd party accessory installed near the bottom of the aircraft. The latter is usually what causes this problem.

 

[old man mavic]

there is one thing that stands out to me as i read this thread,and that is why would anyone descending their Mavic have the throttle stick in the full down position,unless they were landing,you do not need to go full down to get the Mav to descend no matter where you are flying it just seems strange to me

 

[ManBearPig1989]

I am. Forced Landing mode was being initiated each time you had the throttle in the full down position while the downward sensors were detecting an obstacle close to the bottom of the aircraft (as it's designed to work).

You either have a problem with your downward sensors or you had some type of 3rd party accessory installed near the bottom of the aircraft. The latter is usually what causes this problem.

There is absolutely no accessory on the drone. I should note that the drone descends just fine anywhere else. Also, with my throttle fully down elsewhere it doesn't land until close to ground - as it should. Is the sensor sonar or something? I am genuinely confused as to what on earth would be causing the sensors to randomly start glitching only in those 2 locations.

 

[Meta4]

As far as I can tell, the downward sensors were completely clear.
This doesn't happen at any other location hence why I thought it might be due to the area. Are you absolutely certain that it's not due to the flight being listed in a national Park? That seems to be the only common factor.
No accessories whatsoever have been installed on the drone. This doesn't happen anywhere else when flying and descending - Only over the two waterfalls listed in the national Park regions.

Look at the VPS data here: DJI Flight Log Viewer - PhantomHelp.com
For most of the flight VPS altitude is showing numbers close to 1ft.
If the ground below the drone is further than 10 metres, the sensors should read nothing and show NA.

Was the drone over a cliff edge with the ground a long way below?
If so it should have shown NA for most of the flight.
That is the issue.
It has nothing to do with national parks or your location.
If you think it only happens in national parks you should do some testing at home and put the drone up more than 10 metres above the ground and see how VPS is working.
Does it give believable readings from 0-10 metres and then show NA when above 10 metres?

 

[ManBearPig1989]

Look at the VPS data here: DJI Flight Log Viewer - PhantomHelp.com
For most of the flight VPS altitude is showing numbers close to 1ft.
If the ground below the drone is further than 10 metres, the sensors should read nothing and show NA.
That is the issue.
Was the drone over a cliff edge with the ground a long way below?
It has nothing to do with national parks or your location.
If you think it only happens in national parks you should do some testing at home and put the drone up more than 10 metres above the ground and see how VPS is working.
Does it give believable readings from 0-10 metres and then show NA when above 10 metres?

The drone was over a valley with the valley floor a long way down. At home the drone flies normally with the altitude reading and bottom sensor functioning normally - that is it detects ground when in close proximity and lands, yet when at height it functions normally. Hence why I'm extremely confused as to why it only has this issue in these two locations. I'm not at home currently but I can upload a log from a home flight if it helps.
Edit:
Just checked the log in the site you linked for my home flight and it is functioning as intended. This reinforces my point that this is only occurring at Kondalila and Mapleton falls. Are the bottom sensors sonar or something?

 

[Meta4]

[QUOTE="ManBearPig1989, post: 756931, member: 90219"At home the drone flies normally with the altitude reading and bottom sensor functioning normally - that is it detects ground when in close proximity and lands, yet when at height it functions normally. Hence why I'm extremely confused as to why it only has this issue in these two locations. I'm not at home currently but I can upload a log from a home flight if it helps.
Edit:
Just checked the log in the site you linked for my home flight and it is functioning as intended. This reinforces my point that this is only occurring at Kondalila and Mapleton falls. Are the bottom sensors sonar or something?[/QUOTE]
Correction ... It used to fly normally at home.
You need to do some testing now, after the problem flight rather than relying on a flight done a week ago.
The bottom facing sensors are ultrasonic and as shown were giving a false reading for the Kondalilla flight.
That is indisputable as it's clearly shown in the data.
The important question you need to find an answer for is: Are the VPS sensors still giving false data?

 

[ManBearPig1989]

[QUOTE="ManBearPig1989, post: 756931, member: 90219"At home the drone flies normally with the altitude reading and bottom sensor functioning normally - that is it detects ground when in close proximity and lands, yet when at height it functions normally. Hence why I'm extremely confused as to why it only has this issue in these two locations. I'm not at home currently but I can upload a log from a home flight if it helps.
Edit:
Just checked the log in the site you linked for my home flight and it is functioning as intended. This reinforces my point that this is only occurring at Kondalila and Mapleton falls. Are the bottom sensors sonar or something?

Correction ... It used to fly normally at home.
You need to do some testing now, after the problem flight rather than relying on a flight done a week ago.
The bottom facing sensors are ultrasonic and as shown were giving a false reading for the Kondalilla flight.
That is indisputable as it's clearly shown in the data.
The important question you need to find an answer for is: Are the VPS sensors still giving false data?
[/QUOTE]
The Kondalila flight was not the first time this has happened. Every single Mapleton falls flight this has occurred. The home flight was after all the Mapleton falls flights which gave the exact same issue. Every single flight away from those two problem locations function absolutely fine. I actually had a flight on my tablet when I got home, I'll upload that when I get home. The entire reason I uploaded the other home flight was to show that the sensor issue only occurs at the falls. Given the sensors are ultrasonic is there a possibility of the falls sound bouncing off the valley and disrupting the sensor?