Hep me figure out why impending water landing(sinking) wasn't detected

mz-in-cali · Jun 14, 2019

Hi. I was trying to take a picture of a reservoir, from a low angle as if I were on a boat, and ended up sinking into the water.

Previously I had experimented with my pool, and the drone detects the water and stays a few feet above the water. In this case, the drone gave me one warning which I saw very briefly before it disappeared and then I lost contact with the drone - probably at the moment it sank. I don't know what that warning was, so part of this exercise is to figure out what the drone just warned me about a second or two before disappearing.

I'm not trying to blame DJI, because they do warn you that water may not be detected properly, but given that it detects water over my pool, I am trying to figure out what the drone was seeing/reporting, and whether it did actually think it was over an obstacle, and was carrying out an order to land.

Here is a link to the logs:

Dropbox - File Deleted - Simplify your life

www.dropbox.com

I appreciate your thoughts and help.

Thank you.

mz

ps. here is a beautiful picture from the same flight.

Not A Speck Of Cereal · Jun 14, 2019

mz-in-cali said:
I'm not trying to blame DJI, because they do warn you that water may not be detected properly

I think the key is there: the water may not be detected. Which means that the confidence you gained with your pool experiments was unwarranted.

I flew over water a couple of days ago (a couple of feet) and did not take my eyes off the AC, even for a second, not giving trust in the avoidance systems.

Chris

mz-in-cali · Jun 14, 2019

I was looking at the water with the camera angled down, but the surface was so smooth I couldn't make out exactly how close I was. I think there was enough of a lag that at the point that I decided I was close enough, it was too late.

I'm hoping that the logs will have some teachable info.

Hauptmann · Jun 14, 2019

The downward sensor sees light reflected from the surface of the water, and "thinks" the A/C is further from the surface than it actually is. The A/C is then instructed to descend. Splash!
Floatplane pilots have the same problem when attempting to land on glass-smooth water--they don't know where the surface is!

Phantomrain.org · Jun 14, 2019

We fly over the water everyday, and we learned quickly , never fly with the sensors on when pretending you are on a boat.

Phantomrain.org
Gear to fly your drone in and out of the storm.

Meta4 · Jun 14, 2019

mz-in-cali said:
I'm not trying to blame DJI, because they do warn you that water may not be detected properly, but given that it detects water over my pool, I am trying to figure out what the drone was seeing/reporting, and whether it did actually think it was over an obstacle, and was carrying out an order to land.

I'm not trying to blame DJI, because they do warn you that water may not be detected properly

1. Your sensors aren't magic and various situations can make things tricky for them.
Here are the warnings from the manual.

2. Looking at your recorded flight data:
You flew the drone nearly a mile away and descended 200 feet toward the lake.
You would have had no visual on the drone and relied on the camera's view.
The water was dead calm with a surface like a mirror.
At 7:17.2 you went full down with your left stick from -20ft
The Mavic went down at 8 ft/sec
You kept the left stick full down for 22.2 seconds until 7:39.6 when the drone splashed.

There were no warnings as the sensors did not detect anything, as per the warnings in the manual.
You had no direct visual reference for the drone's proximity to the water.
The view through the very wide angle lens would have made the water appear further away than it was.
You drove the drone into the water.

RayOZ · Jun 15, 2019

mz-in-cali said:
I was looking at the water with the camera angled down, but the surface was so smooth I couldn't make out exactly how close I was. I think there was enough of a lag that at the point that I decided I was close enough, it was too late.

I'm hoping that the logs will have some teachable info.

The surface was so smooth you can’t tell with your own eyes how close to the surface it was. Don’t assume your drone could tell the difference too.

Hayabusa · Jun 17, 2019

I brought this up ages ago but I wish you could turn on minimum height restriction. In this case you could set it to whatever distance above water and the drone would not go below those numbers. I fly mostly over water and always looking for those real close shots or flyovers. I am always concerned that my big fat fingers might be slightly pulling stick down instead of just a yaw to right or left. I would love this feature. Would give me piece of mind knowing that it will not go any lower than what I set it at.
Thoughts

AMann · Jun 17, 2019

Hayabusa said:
I brought this up ages ago but I wish you could turn on minimum height restriction. In this case you could set it to whatever distance above water and the drone would not go below those numbers. I fly mostly over water and always looking for those real close shots or flyovers. I am always concerned that my big fat fingers might be slightly pulling stick down instead of just a yaw to right or left. I would love this feature. Would give me piece of mind knowing that it will not go any lower than what I set it at.
Thoughts

Since the drone cant measure its height AGL without the sensors operating normally, it would only be able to measure its height relative to the homepoint and not AGL somewhat accurately within +- a meter or so using it’s barometric pressure sensor.

Gazmg · Jun 17, 2019

Ive never had problems flying over water if it seems like its going to drop increase throttle (Hence in line of site).

Watch this experiment ...very informative.

Air_Joe · Jun 17, 2019

I would have use some floats on my bird if i wanna get a footage that near water.
Bird went for swim in salt sea water before, cant afford to take anymore risk.. [emoji846]
Good luck pal..

Hayabusa · Jun 17, 2019

AMann said:
Since the drone cant measure its height AGL without the sensors operating normally, it would only be able to measure its height relative to the homepoint and not AGL somewhat accurately within +- a meter or so using it’s barometric pressure sensor.

I don’t know how it all works but you would think if I was able to say no
Lower than 5’ or -45’ it would simply not go under that number. I would love to be able to film and not have to worry about it dropping lower than I want. I do a lot of flying with goggles over water filming moving boats etc...
but as you say, must be a reason not to add this safety measure.

AMann · Jun 17, 2019

Hayabusa said:
I don’t know how it all works but you would think if I was able to say no
Lower than 5’ or -45’ it would simply not go under that number. I would love to be able to film and not have to worry about it dropping lower than I want. I do a lot of flying with goggles over water filming moving boats etc...
but as you say, must be a reason not to add this safety measure.

Programs like Litchi have height settings for that, but with waypoints and AGL is based from the homepoint. There may be another program that will do it too for manual flights, someone will link it if there is.

Meta4 · Jun 17, 2019

Hayabusa said:
I brought this up ages ago but I wish you could turn on minimum height restriction. In this case you could set it to whatever distance above water and the drone would not go below those numbers.

Hayabusa said:
Lower than 5’ or -45’ it would simply not go under that number. ...
but as you say, must be a reason not to add this safety measure.

Must be a reason?
Post #6 explained the reason.
The sensors were unable to detect the water surface, so setting a minimum height above the water would not have helped.
Just as having collision avoidance sensors did not help.