Litchi locked me out, crashed!

[BudWalker]

I would turn all of the sensors off when flying litchi. I wouldn't want a programmed sequence to be effected by a false obstacle.




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I suspect that even if OA is turned off it won't be disabled during an RTH. I won't be trying to confirm this with my Mavic.

 

[znuttyone]

I would turn all of the sensors off when flying litchi. I wouldn't want a programmed sequence to be effected by a false obstacle.




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Not sure how many times people have to keep being correcting this for it to sink in, , but i will repeat what others have stated., this is a bug with the mavic / OA/ RTH feature.. so does not matter what app is in use if the conditions are met, you get a repeat. I tested this and see the same behavior just using the DJI Go app. Luckily I spotted this thread and have been watching out for this when flying into the sun ( morning or evening) . I will say I never saw this behavior with the P4, but I also did not test specifically for it, but I flew a ton of flights at sunset and sunrise and never experienced this. First day I got the mavic, I experienced it, seems it is more susceptible. BTW I have the latest firmware.. so it is not fixed yet.

 

[adiru]

Flying today with my VR goggles and the Litchi app. Flew for awhile back and fourth around my house. Went NE of my house over a hay field for one last pass. Wide open in the country, few houses, nothing else. Was headed back toward my house, probably about 200-300 yards out and about 200 feet high, I think. I got a low battery warning coming toward my house, battery was at 25%. Mavic just stopped in the air, wouldn't do anything. So I punched Return to Home and it started rising. My RTH height was set at 300 feet. But it just kept going.....up, up, up!! I know the height on Litchi app was set at Max, which was 1639 feet I believe, though I had no intention of climbing that high. But the drone did. As it got higher and higher I couldn't get any control, so I yanked the cord from the phone with the Litchi app and ran in the house and grabbed the phone with the DJI Go 4 app. Headed up the road in my truck as it was connecting, trying to get it do anything, but to no avail. Once I connected, I could see that it had risen all the way to 1639 feet and the battery was down to 9%!! Then it tried to emergency land, but 9% wasn't near enough, I believe it got to 400 feet or so and dropped. Into some soft grass, so the damage wasn't as bad as expected.

Broke one prop (No biggie), and it looks like one landing leg is a bit broke where it attaches to the body (No biggie), but the camera is trashed. Looks like it landed right on the camera (of course) and jammed it up into the plastic cage looking thing about.....the foil looking area under those plastic pieces is dented in and the camera is hanging loose and has a broken wire.

I had read somewhere that using the Litchi app doesn't void the warranty, guess we'll see what DJI has to say, can't understand why I suddenly had NO CONTROL at all when I tried RTH, still had plenty of battery for that. Why the heck would it lock me out, and climb to maximum height? One lesson is to make sure and set that to 400 feet, didn't bother to do it, wasn't planning on going very high. If that max height was set lower maybe when it locked me out it wouldn't have risen so high, then when it finally decided to land on it's own, it would have had plenty of juice to do so....then probably just a nasty landing and nothing else.

No DJI Refresh, State Farm insurance, but hope I don't have to make a claim less than a month into it lol.

Any thoughts on what the heck happened?

One nasty thing is notices is if you set critical to 15% on the DJI, Litchi will revert it back up to 25%, and then when using the Litch app you are stuck at 25%. this litchi bug is probably the first in a chain of events that caused your crash.

very first thing you should have done, before punching anything, is the red pause button, this would have overrode Litchi and should have overrode any bad RTH entirely. then you should have immediately disconnected the cord microusb to the app/phone/tablet and revert to rc only. Other's have suggested to toggle/cycle the sports mode switch and/or leave it in sports mode to disable any faulty OA.

at 250 years out and 200 feet in "wide open country" it should have been visible, at the very least you can use the crude rudimentary data values like distance, height, etc to find your way back manually without using any RTH at all.

I would have just pushed forward, and looked at my distance, if it was deceasing then I'd know that I'm flying in the general direction, you can use a simple version of "dead reckoning" to figure out if you are at least getting warmer or colder.(all else fails as last resort use the RTH but I don't think it would even have come to that)

then when it gets into visual range, just like it manually.

===


you wasted too much time trying to get the DJI app to work on a different device after the Litchi app failed you. time was of the essence, esp on a low battery and you knew it was climbing.

if winds were much faster at higher alts that day it could have also blown away since it seemed to have been climbing that whole time.

seems like automation (Litchi) already failed you, really not sure why you didn't take manual controls and landed it yourself instead of RTHing when the craft already probabbly got confused.

Always remember first priority is to fly the plane. Automation is only there to help, when it screws up, that is when you take over as the pilot.

And imho, as of now, Litchi is too buggy, I have it, used it, won't trust it for anything important if I didn't already have spare props and DJI Care.

 

[deltalimatango]

...

Hopefully DJI will fix it based on the fact that RTH did not function, chances are that since I was using Litchi, they won't. Then it's a State Farm claim after only a month of insurance.....and chances are they will either dump my Drone policy or ask for a deductible next time.

How is this DJI's fault to fix. You were not using DJI Go, but were using Litchi. The fault seems to on the fault of the Litchi app, not the DJI Go App.

 

[adiru]

How is this DJI's fault to fix. You were not using DJI Go, but were using Litchi. The fault seems to on the fault of the Litchi app, not the DJI Go App.

I'm no fan of DJI, but in this case, its almost 100% Litchi fault combined with user error.


it sounded like OP was already on the way back just about to land, merely 250 m out.
So whatever other factors might have contributed to this accident, it very well never would have come into play if Litchi didn't stupidly revert to the higher 25% and started this whole chain of events in the first place

then when it did happen, OP wasted too much time, precious moments that could have saved the flight. And he wasn't prepared, had to run to truck to get another device to get the DJI app after Litch app already failed him. He would have been better off giving up on trying to reconnect to any device/app at that point, and didn't realize the priority was to get the mavic down first, not let it continue to rise. He should have just taken manual controls at that point, the Mavic wasn't that far away at first, and with "wide open country" he could have landed it anywhere. by the time it hit critical bat level it was already too late since too much height and it takes Mavic way longer to get down than to get up.

 

[znuttyone]

And imho, as of now, Litchi is too buggy, I have it, used it, won't trust it for anything important if I didn't already have spare props and DJI Care.

There are for sure things that are buggy in Litchi, but this is not one of them.. as already pointed out before by others. I know this is a long thread but if you read it and pay attention there are key facts.
1- The analysis done by @BudWalker of the flight record data shows that the Mavic was in RTH mode and was climbing when it detected an obstacle and quit climbing when it did not detect and obstacle.
2- the Pilot @Jr. Stafford provided the context, he was in an open hay field with above any obstacle's late in the day and based on the flight data the AC was flying into the sun
3- DJI covered repairs under warranty
4- others including myself have seen this behavior using DJI GO.

So this is not a Litchi issue it is a bug in the mavic firmware in relation to obstacle avoidance and could happen no matter what app you are utilizing if you have RTH Obstacle Check set.
I preformed some test tonight will provide details on how to re-produce this .. tested it and 3 out of 3 times using DJI Go with the Mavic at the latest firmware. In all three cases, preformed the exact same way, climbed above the RTH height set in the app and the controller was flashing Obstacle. Turing off 'RTH Obstacle Check' flying under the exact same conditions did not exhibit this behavior.

 

[znuttyone]

I'm no fan of DJI, but in this case, its almost 100% Litchi fault combined with user error.


it sounded like OP was already on the way back just about to land, merely 250 m out.
So whatever other factors might have contributed to this accident, it very well never would have come into play if Litchi didn't stupidly revert to the higher 25% and started this whole chain of events in the first place

then when it did happen, OP wasted too much time, precious moments that could have saved the flight. And he wasn't prepared, had to run to truck to get another device to get the DJI app after Litch app already failed him. He would have been better off giving up on trying to reconnect to any device/app at that point, and didn't realize the priority was to get the mavic down first, not let it continue to rise. He should have just taken manual controls at that point, the Mavic wasn't that far away at first, and with "wide open country" he could have landed it anywhere. by the time it hit critical bat level it was already too late since too much height and it takes Mavic way longer to get down than to get up.

I would certainly agree the operator could have handled this situation and probably landed safely, but I have been in situations where something goes wrong and you sometimes do not have the muscle memory to react as you should, and besides he spent the money on the unit and has probably beat himself up on how he might have handled it better

In any case , I will say it again.. Litchi has its bugs and issues , but this one is not theirs. Its in the Mavic and its handing of "RTH Obstacle Check"

 

[adiru]

I would certainly agree the operator could have handled this situation and probably landed safely, but I have been in situations where something goes wrong and you sometimes do not have the muscle memory to react as you should, and besides he spent the money on the unit and has probably beat himself up on how he might have handled it better

In any case , I will say it again.. Litchi has its bugs and issues , but this one is not theirs. Its in the Mavic and its handing of "RTH Obstacle Check"

In that case the Mavic is not that smart for a so called smart drone.

RTH OA glitched, but a lot of other components were working.

Mavic knew the location of the RC, as well as GPS of its home point, and battery %, its height, etc etc etc
At some point, it should have figured out that if it kept climbing and climbing it would run out of juice before it could ever get down and thus fall out of the sky like a rock.
So between two competing conflicts, in such a situation, it should have overridden the RTH OA check automatically and slowly descended for a straight downwards landing right where it stood. This decreases the chance that it would hit anything even if the OA was working correctly, and since the alternative is that it would drop out of the sky anyway once battery was too low, the smart thing to do would be to stop climbing, and descend straight down, while alerting the owner what it was doing so that it can be located easily.... (and/or prompting the pilot to give him to option to take full manual control or to consent to either disabling OA for the remainder of RTH, or some other alternative)

Plus a truly smart drone with the telemetry that Mavic collects would have figured out that on the outbound there wasn't such obstacles at high alts, so why on the inbound suddenly it had to surmount a seemingly 1600 foot mountain? Doesn't even make any sense. should have at the very least recognized that possibly that OA glitched and asked pilot if he wished to consent to disable OA for the remainder of the RTH in order to get back down before battery went to nil.


and as for the whole "mavic flying into the sun" thing... Mavic has GPS, (Time via GPS TIME), knows altitude, has compass, has IMU, gyro, gimbals, so it knows exactly which way it is pointed in space, and all it needs is a simple star/planetary database so it can recognize where the sun is and where the moon is so it doesn't mistake these for obstacles it could hit. at the very least, it should be smart enough to know that "hey I'm flying into the sun, but I don't know for sure if there is an obstacle as well or if it is just the sun, maybe I should prompt the pilot for him to take manual control and/or give him the choice to decide whether or not I should disable OA" for remainder of this RTH."

Why can't this sort of logic be programmed into the firmware?

 

[znuttyone]

Ok so if anyone wants to duplicate the conditions to see this behavior, here are the steps.
Perform this test when the Sun is low on the horizon , 2 hours before sunset or less will do.
Steps
1- Set "RTH Obstacle Check" on.
2- Set a reasonable Return-to-Home Altitude above any obstacles that would be in the flight path (45M is what I had)
3- Set Max Flight Altitude to a distance higher than the RTH Altitude ( 200M is good for this test, unless you want to see what @Jr. Stafford saw and have the AC go to 1640ft, not advisable..
3-Set the home location
4-Fly the Mavic above your RTH Altitude, Fly East from your position 100ft or so, in my case it was 450ft.. and 150ft high
5- hit RTH.

Observations: as soon as I hit RTH the AC began to climb, the controller was cycling between obstacle and Going Home, but basically it was climbing vertically and not moving back to home.

I did this test 6 times, 3 times with RTH Obstacle check set, 3 times with it off. All 3 times with RTH Obstacle set performed the same.. Climbed well above the RTH Altitude. The 3 times with RTH Obstacle Off, AC rose to the predefined RTH Altitude and returned home.

I also tested Flying west so return was not into the sun, in this case the controller never flashed Obstacle and the AC came home at the RTH altitude.

I suspect that if I did this right after sunrise and reversed the direction Fly west, RTH to the east, I would see the same behavior.
If I get time will test that as well.

Ok I realized I should probably advise those that want to test this how to get the AC home if you test this..
Simply go into Sport mode and fly it home.. or cancel call him, go into the advanced settings under visual navigation settings in the DJI Go app and Turn off "RTH Obstacle Check" , then go back and hit RTH.. the AC will fly back home and land on its own.

 

[adiru]

Ok so if anyone wants to duplicate the conditions to see this behavior, here are the steps.
Perform this test when the Sun is low on the horizon , 2 hours before sunset or less will do.
Steps
1- Set "RTH Obstacle Check" on.
2- Set a reasonable Return-to-Home Altitude above any obstacles that would be in the flight path (45M is what I had)
3- Set Max Flight Altitude to a distance higher than the RTH Altitude ( 200M is good for this test, unless you want to see what @Jr. Stafford saw and have the AC go to 1640ft, not advisable..
3-Set the home location
4-Fly the Mavic above your RTH Altitude, Fly East from your position 100ft or so, in my case it was 450ft.. and 150ft high
5- hit RTH.

Observations: as soon as I hit RTH the AC began to climb, the controller was cycling between obstacle and Going Home, but basically it was climbing vertically and not moving back to home.

I did this test 6 times, 3 times with RTH Obstacle check set, 3 times with it off. All 3 times with RTH Obstacle set performed the same.. Climbed well above the RTH Altitude. The 3 times with RTH Obstacle Off, AC rose to the predefined RTH Altitude and returned home.

I also tested Flying west so return was not into the sun, in this case the controller never flashed Obstacle and the AC came home at the RTH altitude.

I suspect that if I did this right after sunrise and reversed the direction Fly west, RTH to the east, I would see the same behavior.
If I get time will test that as well.

So what is the best procedure to correct this for those with OA already on at the time of the incident?
I read about the cycling of sports mode
Have you tried the red pause button, does it stop the Mavic from climbing when in critical bat RTH + OA, until user can figure out what to do?

 

[BudWalker]

There are actually two max Heights. There is the one that the pilot sets, but, there is also an absolute max height set when the flight controller is configured during start up. That absolute max height is 500 m. During an RTH the Mavic will climb past that pilot set max height to the absolute max height if it is trying to avoid an obstacle.

 

[znuttyone]

In that case the Mavic is not that smart for a so called smart drone.

Although I do not like this behavior and agree it is not very smart logic, overall Mavic is pretty smart, has big improvements in its ability to land softly and in the same position it took off. So although it has it's negatives, overall it's still a great unit.

RTH OA glitched, but a lot of other components were working.

Agree..

So between two competing conflicts, in such a situation, it should have overridden the RTH OA check automatically and slowly descended for a straight downwards landing right where it stood.

I think that is what is would do once you cross the critically low battery threshold, but the operator can modify this to a level that would not allow you to descend in time, and you can cancel the action, so ultimately you need to know how to operate the unit. I will say DJI does not do a good job documenting a lot of these nuances.

Plus a truly smart drone with the telemetry that Mavic collects would have figured out that on the outbound there wasn't such obstacles at high alts, so why on the inbound suddenly it had to surmount a seemingly 1600 foot mountain? Doesn't even make any sense. should have at the very least recognized that possibly that OA glitched and asked pilot if he wished to consent to disable OA for the remainder of the RTH in order to get back down before battery went to nil.

Agee, they need to improve the logic of RTH with OA, and OA overall, it is really sensitive compared to P4 to the point I have been turning off more often with the mavic vs P4 where I left it on a lot of the time as it did not impact smooth video shooting.

and as for the whole "mavic flying into the sun" thing... Mavic has GPS, (Time via GPS TIME), knows altitude, has compass, has IMU, gyro, gimbals, so it knows exactly which way it is pointed in space, and all it needs is a simple star/planetary database so it can recognize where the sun is and where the moon is so it doesn't mistake these for obstacles it could hit. at the very least, it should be smart enough to know that "hey I'm flying into the sun, but I don't know for sure if there is an obstacle as well or if it is just the sun, maybe I should prompt the pilot for him to take manual control and/or give him the choice to decide whether or not I should disable OA" for remainder of this RTH."

Why can't this sort of logic be programmed into the firmware?

Excellent point and suggestion.

 

[znuttyone]

So what is the best procedure to correct this for those with OA already on at the time of the incident?
I read about the cycling of sports mode
Have you tried the red pause button, does it stop the Mavic from climbing when in critical bat RTH + OA, until user can figure out what to do?

You could as you suggest, just go into sport mode and fly it home manually using the console view (radar/compass view) or you can cancel RTH, AC will hover, go into settings and disable RTH Obstacle Check , then hit RTH again.

 

[znuttyone]

There are actually two max Heights. There is the one that the pilot sets, but, there is also an absolute max height set when the flight controller is configured during start up. That absolute max height is 500 m. During an RTH the Mavic will climb past that pilot set max height to the absolute max height if it is trying to avoid an obstacle.

I did not see this when i tested it, it seemed to honor the pilot max altitude, I will test this again to be sure.

 

[znuttyone]

I suspect that even if OA is turned off it won't be disabled during an RTH. I won't be trying to confirm this with my Mavic.

I tested it if you turn "RTH Obstacle check" off in the advanced settings screen,

I did not see this when i tested it, it seemed to honor the pilot max altitude, I will test this again to be sure.

Ok tested this again this morning, so at sunrise flew AC west, RTH towards east, facing sun. Same behavior, and BTW @BudWalker , you are correct it ignores the pilot set-able Max Altitude and keeps climbing.. I had 250M set, but it keep climbing well past that to 304M ( 1000ft) when I decided to cancel and override the RTH, flipped it into sport mode and flew it down manually .

Also a friend of mine pointed me to another thread Forward Sensors and Glaring Sun , where someone had stated they used the DJI Assistant to re-calibrate the sensors and it resolved the sensitivity. I decided to try that , but no help. Still reacts the same as before calibration.

Summary:
Until DJI issues a fix ( tested 01.03.0400) , no matter what app you are using (DJI or Litchi) If you are going to fly when the sun is low on the horizon and your RTH path will be into the sun, plan ahead.
Either
1- be prepared to take manual control and bring it back home manually ( flip to sport mode)
2- or disable 'RTH Obstacle check" in the advance settings of the Visual Navigation Settings
Attached is a picture of what the Mavic was seeing.

 

[rydfree]

Just read this thread and when I first got the Mavic I flew with the DJI app for the first few flights . This happened to me late in the day on about my 3rd flight when I purpously hit RTH at 1500' out and around 100' high just to see if it was going to work correctly . I switched to sport mode and took over from about 1000 feet out and 350' high and flew it back by watching the distance and altitude telemetry. I switched to Litchi and have never had a problem although Obstacle Avoidance has never been turned on in the menu. I really have no use for it unless I were to be flying low around trees or buildings . I have never had that feature on any of my other drones so I just never use it . It was turned on in the DJI app though. I read that evening while searching the forums and saw where it was an issue . LItchi has been flawless so far and all I ever use. I've flown multi-rotors since 2010 and planes/helicopters before that so flying a racing drone in full manual with no self leveling is no biggie so that helps . You have full control over the craft without a phone attached or the app . Never let automation be a crutch . Learn to fly the plane is the best advice .

 

[TheoMatthias]

Any update on this issue? I know there have been several Mavic firmware updates since znuttyzone tested this earlier in the year with version 01.03.0400. BTW - this thread should be required reading for any Mavic pilot regardless of the app they are using.

Theo