Well, it's true - Don't do this..

[Debel]

In the user guide for my Mavic Air 2 it clearly states. Do not hover low over water as the downward sensor will be disabled when detecting the water surface.

Well, I can say this is true.. I "parked" my MA2 around 1 meter above water and only 3 meter from land (Stupid me), because I was fiddling with some video settings, and suddenly the drone just dropped into the water with no sticker input. It just touched the surface without going under, and I was able to lift et up again and head towards land. But, just above land and around 2 meter up in the air, the drone simply shut down and fell to the ground as a rock. Gimbal destroy and drone soaking wet.

Sent it to DJI and just got the replacement, so all good for now.. But..

2 lessons learned;

1. Do not hover low over water
2. Read the user manual

 

[SmilingOgre]

In the user guide for my Mavic Air 2 it clearly states. Do not hover low over water as the downward sensor will be disabled when detecting the water surface.

Well, I can say this is true.. I "parked" my MA2 around 1 meter above water and only 3 meter from land (Stupid me), because I was fiddling with some video settings, and suddenly the drone just dropped into the water with no sticker input. It just touched the surface without going under, and I was able to lift et up again and head towards land. But, just above land and around 2 meter up in the air, the drone simply shut down and fell to the ground as a rock. Gimbal destroy and drone soaking wet.

Sent it to DJI and just got the replacement, so all good for now.. But..

2 lessons learned;

1. Do not hover low over water
2. Read the user manual

Yikes! Thanks for sharing! I'll add it to the list. I think I'm going to have to put all of these pointers on flash cards and go over them nightly.

 

[boblui]

I doubt very much if the bottom sensors are to be blamed as I frequently hover and fly my M2P very close to water surface with all sensors turned on. The craft just behaved as if it was over land with the exception that it would not go lower than 1 meter above the water surface compared with 0.5 meter over land.

If you can post the .TXT and .DAT log files of the flight in the phone by following this guide , the real reason can likely be identified.

My M2P below. You can see the VPS data at the bottom of the screen indicating the height above the water surface. Certainly the sensors are not " disabled when detecting the water surface. "

 

[bmwbob]

I think at a certain height they just decides to land by themselves. I had a Mavic mini try to do it once, but caught it in time.

 

[boblui]

I think at a certain height they just decides to land by themselves. .....

Only if you pull the throttle stick all the way down and hold it there for more than a second. I don't believe that's what the OP has done.

 

[vindibona1]

I believe that the MA2 and M2's have different sensor systems than each other. I know the Mini's are notorious for losing altitude when too close to water. In any case, I think I'm going to build some pontoons and maybe buy a wetsuit pack. I've already acquired a length of pool noodle that could be popped on the legs if in doubt. I'm still a chicken-sht when it comes to flying over water. If the thing had a floating water landing, even with pontoons I don't know how I'd recover it if II couldn't take off from the water again.

 

[boblui]

I believe that the MA2 and M2's have different sensor systems than each other.

They are equipped with the same set of sensors at the bottom. One pair of cameras + IR sensors. The camera is for detecting horizontal movement in OPTI/VISION mode and whether the ground is even in autolanding mode. The IR sensor is for detecting distance from obstacles / ground.

I know the Mini's are notorious for losing altitude when too close to water.

I dont recall seeing any any substantiated reports of such occurrence in this forum. The Mini does, however, have a well known problem of uncommanded descent due to propeller deformation and that can happen over land or water. One of the thread on the problem : Mavic Mini uncommanded descent tests

 

[vindibona1]

They are equipped with the same set of sensors at the bottom. One pair of cameras + IR sensors. The camera is for detecting horizontal movement in OPTI/VISION mode and whether the ground is even in autolanding mode. The IR sensor is for detecting distance from obstacles / ground.


I don't recall seeing any any substantiated reports of such occurrence in this forum. The Mini does, however, have a well known problem of uncommanded descent due to propeller deformation and that can happen over land or water. One of the thread on the problem : Mavic Mini uncommanded descent tests

The Mini props are very delicate and can cause instability and directional control problems as well as uncommanded descent. While my M2's props still need to be inspected before every flight, the Mini's need to be looked over extremely carefully as distortions that can be formed in the case can easily go unobserved if not specifically looking for the deformations. I was shocked when I saw what's in the photo below. The props on the M2 are far more robust underneath are protected by a two rubber bumpers, if the props are folded inside of them.

 

[RichR]

The issue with being close to calm water is well documented and not unique to DJI drones. The problem is that if the water is clear enough, under some lighting conditions the surface is very hard or impossible to determine. If the water is relatively shallow (say up to about 2 metres if it's really clear) then the sensor may detect the bed of the lake/river/sea as the surface and happily allow descent into the water. Drones with ultrasonic sensors won't have this issue, but they can be confused by other surfaces (eg ones that scatter the sound pulses rather than reflecting).

This is why most manufacturers of drones with downward facing sensors advise against flying low and slow above water. It's fine if you're aware of the situation and fly in a manner that means it won't be a problem and responding as soon as it appears to be descending unexpectedly. Drones with no sensors on the bottom don't have any warnings as it's your own fault if you go too low

 

[boblui]

The problem is that if the water is clear enough, under some lighting conditions the surface is very hard or impossible to determine. If the water is relatively shallow (say up to about 2 metres if it's really clear) then the sensor may detect the bed of the lake/river/sea as the surface and happily allow descent into the water.

That can be true but even under that circumstance, the drone will not go into the water unless commanded by throttle stick inputs. It definitely will not " shut down and fell to the ground as a rock " as reported by the OP.

 

[RichR]

That can be true but even under that circumstance, the drone will not go into the water unless commanded by throttle stick inputs. It definitely will not " shut down and fell to the ground as a rock " as reported by the OP.

Very true. I was just qualifying why the manual advises against it in general.

 

[Debel]

That can be true but even under that circumstance, the drone will not go into the water unless commanded by throttle stick inputs. It definitely will not " shut down and fell to the ground as a rock " as reported by the OP.

Sorry for not getting back to you guys, some work took my time.. the drone did not "shut down" when hovering, it just lowered it self into the water. I have tried to recall my actions again and again, but even if I for some reason should have hold the down stick down, it normally don't just land in the second.. It usually take some time to invetigate the ground before lowering.. This time it went from hover nice and fine, and then just dropped and touche the surface of the water. It was first after I have raised the drown from the water with my controller, and flew towards land, that the drone shut completely down in mid air, when I was trying to find a suitable place to land. It was flying for around 20-30 seconds or so after it touched the water, before some water inside caused the shut down. Hope this clears things. I will try to extract the flight log, also for my own curiosity, to see what actually happened. I have got a new drone from DJI by now, so I will definitely take my precausions next time over the lake

 

[DanMan32]

Even with ultrasonic in P3 days, DJI training videos recommended caution flying low over water. I believe though it was more for the vision position sensor (bottom camera) having issues detecting a pattern to lock onto, or moving waves being tracked as a stationary pattern.

 

[boblui]

....even if I for some reason should have hold the down stick down, it normally don't just land in the second.. It usually take some time to invetigate the ground before lowering.. This time it went from hover nice and fine, and then just dropped and touche the surface of the water. ....

There can be many reasons for drones to go down on it's own. Only the flight log can tell the actual reason. This is a recent report on such incident : Lost Drone Not Sure Why . It turns out that the controller was faulty.

 

[hiflyer201]

liked all the comments. Very interesting subject.

 

[Otisangb]

I was messing around with low flight over water and my results were very similar to the below video.
This Video
I plan on doing this experiment again when I get a chance because I did not document it at all as my wife was flying around and I just jumped in for a couple of minutes to test this out. What I found was that with the downward vps disabled the ac wanted to descend on its own into the water and I had to keep adjusting height. With the downward vps enabled the ac fluctuated in height but was more reluctant to just drop. I kept landing protection off for both flights. The water was very clear with small waves coming in.

When I repeat this I will better document and will start a new thread and post the findings. I would post the data I have but we made three flights that day and really am not sure which one it was or at what time and was not video recording. In the past I was given and gave the recommendation to turn off vps but after what I physically saw I am not so sure anymore. The one thing I do is turn landing protection off so I don't auto land.

 

[Capt KO]

The search function here will show Many uncommanded decents into water while hovering. Give it a look. Scary. Bottom sensors unable to distinguish solid flat non contrasting surfaces. Including snow and sand. Mavic Mini most susceptible to this problem.
OP thank you for the reminder. ? it happens

 

[boblui]

What I found was that with the downward vps disabled the ac wanted to descend on its own into the water and I had to keep adjusting height. With the downward vps enabled the ac fluctuated in height but was more reluctant to just drop.

With VPS off, the craft will not be able to detect the height over the water surface so all it can only rely on will be the barometer which is less precise. In such state the craft will drift upward or downward randomly with equal probability. There should not be any biased tendency to "descend on its own into the water ".

I kept landing protection off for both flights. The water was very clear with small waves coming in.

If landing protection is off, the drone will go straight towards the water if down-throttle is applied. This is obviously not desirable. I always keep landing protection on so that the craft will automatically keep a safe distance ( 1 meter for M2 ) from the water surface even if the throttle stick is moved downward unintentionally. With that setting you can fly the drone at maximum speed and maintain a height of 1 meter above the water surface without risking the craft getting wet due to momentary wrong stick inputs.

 

[boblui]

The search function here will show Many uncommanded decents into water while hovering.

Among all the ditching cases reported here with flight log supplied, I have seen none caused by the bottom sensors not working over water surface. The uncommanded decent problem of the Mini is due to wrapped props. DJI has subseqently enhanced the FLY app to help detecting which props are bad. Since then the number of reports on uncommanded decent has dropped substantially.

Bottom sensors unable to distinguish solid flat non contrasting surfaces. Including snow and sand. Mavic Mini most susceptible to this problem.

There are two sensors at the bottom, an IR sensor and a pair of cameras. Only the cameras need to see images with sufficient contrast in order to work ( performing vision-based XY positioning ) . If the image is not good for the purpose, the worse thing that can happen is the craft drifting horizontally. It will NOT go into the water becasue of that.

There is no evidence that the Mini's bottom sensors are poorer in any regards.

 

[kidroc]

It’s the nature of the way they work there not perfect they can and will move up down side to side as the systems are not exact give it a good meter in all a uses to move next time