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RTH altitude above max - nearly lost my quad.

CrowsFeet

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I believe this is a major bug. But maybe I did something wrong.

I flew in an area with a restriction of 60m altitude. Did a hyperlapse. Quad was about 300m away. Was shooting a pier - so quad over the sea.

With 4 shots of a 250 shot video to go, I got a battery low warning and offer to RTH. I canceled to allow completion. I’d fly back in the next 10 seconds and there was enough battery for that easily.

It then quickly showed a forced RTH message. Battery seemed to stop quickly as it completed. Guessing processor usage when it renders the video onboard? So I let it auto RTH

It rose to 65m, turned towards me and - nothing. Just sat there warning me of the battery. I took over. Cancelled automatic RTH and stick forward to get home. I was over the sea.

Quad didn’t move. No matter which direction I went in. Then I got critical battery warning. But quad would not move. Hovering over sea. Maybe 100m from shore.

I noticed the altitude was red. It said 65. I realised I can descend. So went down to 60m and altitude went white again. Then I could move. Loads of beeping and warnings. Quad started descending by it’s self but I could fly toward. Maybe I cancelled the forced landing. Not sure. I was in panic mode. Made it to beach and landed on sand. Safe.

The issue is: why did it rise to above the maximum set altitude (set by the quad when it started up and warned that I was in a restricted zone)?? Because when it went into that area (above the max altitude set, and into a restricted area) - it would not RTH, and when I took over, it would not move. Except down. Which I realise later. Surely the RTH should be the set RTH value, or the max altitude for the area - which ever is lower. A useless RTH of 65 in a 60 is dangerous and neatly cost me my drone.

I opened settings after calming down and the RTH value was indeed 65 and the max altitude had been auto set to 60 based on my location.

Very scary when you quad is about to die - 100m out to sea over the waves! I’d hope DJI can update the logic on RTH altitude and max altitude. Seems very unsafe.
 
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If you go to
DJI Flight Log Viewer | Phantom Help
you will find instruction concerning how to retrieve the flight log. Upload the relevant flight log to that site and post the resulting URL here.
The answers might be in the flight log.

A few points,
if the drone was in critical-low-battery forced-landing mode you can not cancel that but you can keep the drone in the air, for a while, with significant throttle but you need to get the drone down and safe ASAP because, at some point, the drone will simply stop the motors even if the drone is in the air.

I would hand catch rather than land on sand.

From my messing with a Mini 1 or Mini 2 the RTH height can not be higher than the maximum maximum height set by you in the app.
When I reduced the maximum height to below the RTH height the RTH height was reduced to match the new maximum height.
If your RTH height was higher than the maximum set in the app then this is a new behaviour or perhaps something enabled by the restriction zone.
Do not confuse the restriction floor height with the drone's maximum height, they may differ.
Also, if my Mini was above the new maximum height it descended, on its own, to, or just below, the new maximum height.

I do not know if the floor of a restriction zone alters the maximum height setting in the app.
 
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You discovered the issue with the drone maintaining the height limits for you versus the other way around. You basically ran into the “shelf” that was limited to 60 from a spot that maybe was not. The drone was able to to fly upwards to the return to home elevation but ran into its internal rule for no flight at that elevation on the way back. I have seen others get stuck like you did. In a restricted space, you want to set your RTH just below the limit for the area and it will avoid the issue. Seems it would be smart enough to descend to the limit and fly home but it’s not. It will sit at the shelf wall which is unnecessary since it’s making this judgement based on the take off point and not its real height above the terrain. Glad you got your drone back.
 
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The RTH responses of DJI's drones vary depending on which model you're flying. My Mini just climbs to the configured RTH height and flies a straight path home. Others are capable of backing out and retracing the last portions of their flight path before RTH. It's best to study your user manual and run your own experiments in a safe environment to ensure you know what to expect when and if.

If you're flying close to any DJI Flysafe geo-restricted zone, or under a height-restricted zone, the app usually pops up a warning to the effect that RTH may not work if the drone encounters the boundary of such a zone on its return path.

See this previous thread:

nfz-jpg.146233
 
The drone warning does NOT set the RTH or any other altitude maximum when you get a warning. It is just a warning. You flew out of the altitude zone and your RTH altitude took you out of the allowed height.
 
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Log uploaded.

That's pretty cool....
In it, I can see where I got the low battery warnings.... It was around 198 feet. Then it rose up to 207 feet, which it should not have. It did it in RTH. It rose it's self. When flying manually, I go to max height and it stays there. But in RTH, it broke the ceiling, which I believe it shouldn't.

The logic for RTH should be - Go to RTH altitude OR Max Allowed Altitude, whichever is lowest.

Anyway, at 23m 17s, I manually descended. But for a while before that, you can see my right stick trying to move, and it didn't.

At 23m.21, you can see the auto land kick in, over the water. Yet somehow, I managed to fly it to safety. Google earth seems to show low tide, as I had just cleared the water when it went down.

GPS-BRAKE comes in at 21m 24. Not sure what GPS-BRAKE is.... But it's the same time Return to home promptly (Code: 1B030014). is mentioned.

GO-HOME at 22.8. I guess that's when I told it to go home. But you can see no movement. It would not return.

At 22.30, you can see stick forward. But it wouldn't respond.
 
Interesting, did you change the MANUALLY maximum height limit during the flight?
You log shows a behaviour I have NOT seen before and, in my flying, has been IMPOSSIBLE.
If you down load and open the csv of the log you will be able to see what I am taking about.

Column EC shows what I believe to be the max height ceiling "HOME.heightLimit [ft]", at the start of the flight it was 196.9ft / 60m but at timestamp 18:49.6 it changes to 213.3ft / 65m BUT throughout the flight the RTH height, column EP "HOME.goHomeHeight [ft] is 213.3ft /65m.

As I mentioned earlier in my fiddling the set RTH height could not be greater than the set maximum height. Maybe the restriction zone hypothetically 'lowers ' the maximum permissible height to the floor of the restriction with out lowering the RTH height to match it.

When the drone RTH'ed it appears to have attempted to climb to the set RTH height, 213.3ft, and reached 211.6ft at 22:30.2 before perhaps the restriction zone stopped it.

If others concur this might be something you should raise with DJI, it would seem to be a programming flaw to allow a drone to climb INTO a restriction zone via RTH.

Where does the restriction cover?
 
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With regards to the behaviour during forced landing I added a bit to post #2, due to its being an add on you may have not seen it.
ou have control during a forced landing but horizontal speeds will probably be limited and a LOT of throttle will be required to maintain height.

You might like to read the low battery RTH section of the manual, page 16, it details most of the above.
 
At .38 and again at 2.38 there was a warning -
Current RTH route close to GEO Zone(s). Pay attention to the aircrafts position on the map to avoid RTH failure).
This is the first warning you should have heeded.
 
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At 0m 38.2s: Current RTH route close to GEO Zone(s). Pay attention to the aircraft's position on the map to avoid RTH failure).
Yup. It's a warning to check your map. GEO zones are displayed on the app map, even on a blank map if you haven't cached a map display. Your drone's position will show on the map either way.

The warning is so that you'll be aware there's a GEO zone nearby, and the aircraft will refuse to enter or cross any GEO zone it may encounter during an automated RTH procedure, thereby preventing a successful completion of a RTH.

If you still have a solid control signal, you can simply steer the drone around any such GEO zone to avoid a conflict. But, if you've lost control signal, and the aircraft is flying back in an automatic RTH, it may bump into that invisible wall marking the boundary of a GEO zone and go no further, until a depleted battery causes it to auto-land wherever it's at. That's what the warning is for.

In your case you took off within a Blue Authorization zone for the nearby airport. Why it allowed that, I don't know. There is a Red Restricted Zone over the airport's runway, but you're well clear of that. Your flight was conducted underneath the Grey fan-shaped extension from the runway which is a 60m Altitude Zone, again not a problem as long as you remain below 60m (197ft).

At 22m 11.2s: Aircraft entered Geo Zone. Return to Home may be affected. Exit zone promptly.

At that point the aircraft's height is shown as 200ft as it encountered the outer edge of the 60m Altitude Zone. The GEOfence system blocked further entry into that zone. All you needed to do was to descend to less than 60m altitude and the drone would have been allowed to return below that restricted height.

60mZone.jpg
 
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A useless RTH of 65 in a 60 is dangerous and nearly cost me my drone.

At the point where RTH was triggered the drone was still outside the 60m Altitude Zone. So nothing prevented the drone from ascending to its configured 65m RTH height.

But when coming home it encountered the outer edge of the Altitude Zone and was prevented from entering the zone at a height greater than 60m.

Lowering the drone to any height less than 60m would have allowed it to return to you underneath the restricted Altitude Zone of 60m or higher.

Always check DJI's GEO zone map beforehand, or study the map within your DJI Fly app to familiarize yourself with any potential conflicts. Note also, that DJI's maps very often do not correlate accurately with actual legal airspace restrictions. DJI may allow you to fly within areas where it's actually illegal, and/or prevent you from flying in areas where it's not illegal. The actual legalities are the pilot's responsibility to figure out. But it's DJI's GEO zones that will actively interfere with your aircraft's behaviour, which is why it's always important to realize where those zones are.
 
@Zbip57 if the max height change shown in the log is not manual is the restriction zone the reason for it and if so why doesn't it lower the RTH height accordingly?
Or do you happen to know if this i.e. allowing an RTH height that is higher than the set max height, is a new behaviour introduced with the mini 3?
 
@Zbip57 if the max height change shown in the log is not manual is the restriction zone the reason for it and if so why doesn't it lower the RTH height accordingly?
Or do you happen to know if this i.e. allowing an RTH height that is higher than the set max height, is a new behaviour introduced with the mini 3?
It’s been an issue all along. You have to manage your height for the area including return to home. Setting it to 300 feet when nothing in the area is taller than 50 is not reasonable either, even when in unrestricted areas. It’s part of the management of the drone. Restricted areas make it that much more important.
 
Thanks @Yorkshire_Pud
I am 100%sure I never changed the RTH height during the flight. When I fly, I fly very simply. I never change settings. I believe this is the bug. Somehow, the RTH altitude, which I have never changed, changed to 65m, and the maximum height was 60m. It gave me a message when I powered on and had to 'Authorize' the zone. I am in an area where there is a small airport.

At that point, it will set both RTH and Max Height to 60m. I think that is how it works.

After landing, I went into settings, and noted that the max alt was 60m, and the RTH height was 65m. So that's a state, I believe, the controller should never be allowed to get into, and that's the bug.

Here is the area I was flying and you can see the DJI GEO Zones. So as you can see, it's the Ovar area, with a limit of 60m, which covers the area I was in. Not close to any overlaps.

1672271792323.png

Here I am zoomed out a bit further.
1672271852785.png
 
At the point where RTH was triggered the drone was still outside the 60m Altitude Zone. So nothing prevented the drone from ascending to its configured 65m RTH height.
I'd say this is a bug. The drone should not be allowed to automatically fly into a restricted zone. When the drone is powered up, and IF (I didn't) I had the RTH set to 65m, and drone detects a restricted zone and puts up a warning about it, and automatically reduces the max alt to the restricted zone height, surly it should reduce the RTH alt to either the same value, it it was higher than the new max alt?
 
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I am 100%sure I never changed the RTH height during the flight. When I fly, I fly very simply.
I was asking about the maximum height limit, it changed from 197ft 60m to 213ft 65m at timestamp 18:49.6.
Your set RTH height remained constant at 213ft 65m right the way through the flight.
At that point, it will set both RTH and Max Height to 60m.
Unless I am mistaken in the appropriate columns of the csv then I think you are mistaken in that the RTH height was not changed.
I suspect the maximum height limit of 60m was a nominal, automated thing caused by the restriction zone and that you did not manually change the maximum height limit to 60m.
I can not experiment with this as I know of nowhere accessible which is beneath the floor of a reach able flight corridor. But I can vouch for the fact that where I have reduced the maximum high limit to below the set RTH height the set RTH height was reduced to the new maximum height or slightly below it.
After landing, I went into settings, and noted that the max alt was 60m, and the RTH height was 65m.
I suspect you saw the influence of the restriction zone on the maximum height limit and not the 'real' height limit as set by you at some previous time.
From 18:49 to 23:21 the log show the maximum height limit to be 65m 213ft, from there on is drops to 60m 197ft, both changes occur around 1300ft from the home point. From 23:21 onwards the maximum height limit is 60m 197ft.

I stress, the affect of the restriction zone on the maximum height limit is guess work on my part and could be wrong,
.
 
It’s been an issue all along. You have to manage your height for the area including return to home. Setting it to 300 feet when nothing in the area is taller than 50 is not reasonable either, even when in unrestricted areas. It’s part of the management of the drone. Restricted areas make it that much more important.
I think you missed my point and question to Zbip57.
It is my experience that the RTH height can not be set higher than the maximum height limit. Additionally, if the existing maximum height limit is reduced to below the existing set RTH height then the set RTH height is automatically reduced to, or just below, the new maximum height.
In places in this flight the log reports that the set RTH height was above the maximum height limit, by 5m.

I am questioning why that happened and if the software should be altered to reduced the RTH height to below the floor of a restriction since the restriction is now being shown as the maximum height limit.
 
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However, see the map above. I was in a restricted zone of 60m the whole flight.
No, you weren't. That's the whole problem. Zoom in on my image in post#11 above.

You took off and flew most of your flight over the beach below the height and under the 60m Altitude Zone. That's all fine and good.

But a portion of your flight was far enough out to sea that it was out beyond the area covered by the Altitude Zone. Out there you received the low battery warnings and allowed the drone to go into automatic low-battery Return-to-Home. Your RTH height was and is configured to 65m for the entire flight (see column-EP in the CSV log file "HOME.goHomeHeight [ft]"). It was set to and remained at 213.3ft (65m) the entire time.

The drone behaved exactly as it programmed to do. Outside of any restricted zone it ascended to its configured RTH height of 65m before heading for Home, and then it encountered the edge of the defined Altitude Zone. At that point the drone again responded exactly as designed and refused to enter a Geo-fenced area.
I'd say this is a bug. The drone should not be allowed to automatically fly into a restricted zone.
But that's just it. It did NOT automatically fly into a restricted zone! It stopped at the boundary.

This is exactly what the warning messages were telling you. When in automatic RTH, the drone will stop at the boundary of any defined GEO zone and will not be permitted to enter or cross that zone and thus may fail to return home.

If you had been flying it manually at the time it would have behaved exactly the same way. You can always cross under the Altitude Zone as long as you stay below 60m. On either side beyond the defined edges of the Altitude Zone area you can climb to any height you like, but you cannot enter that zone from either side if you are currently flying higher than 60m.

[...] It then quickly showed a forced RTH message. [Low battery RTH ...] So I let it auto RTH
It rose to 65m, turned towards me and - nothing. Just sat there warning me of the battery. I took over. Cancelled automatic RTH and stick forward to get home. I was over the sea.
Quad didn’t move. No matter which direction I went in. Then I got critical battery warning. But quad would not move. Hovering over sea. Maybe 100m from shore.
I noticed the altitude was red. It said 65. I realized I can descend. So went down to 60m and altitude went white again. Then I could move. Loads of beeping and warnings. Quad started descending by itself [critical battery autoland] but I could fly forward...

There's no mystery here.
 
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