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Erratic behaviour of MA2 over water
1219 18 2020-7-6
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Mirek L
First Officer
Flight distance : 609724 ft
Canada
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Hi,

I take my MA2 with me on canoe trips.
I have noticed that behaviour of MA2 over water, especially when there is a bit of light wind or waves, is quite erratic.
I used to fly Spark and land it with no problem on my canoe. The same feat with MA2 is a blood curling and hair raising event.

I suspect that MA2 downward facing sensors are extremelly sensitive to water reflections moving below causing unexpected and very sudden adjustments of MA2 position. This makes landing it on a canoe which is pushed by light waves, a very challenging and risky act.

Please see the following log around 21 min 38 seconds, 22 min 7 sec to 22 min 8.5 sec, 22 min 10 seconds, 22 min 13 seconds, 22 minutes and 15 seconds.
https://www.phantomhelp.com/LogViewer/8XI14QRM38CQ3GBDO5Z5/


I was directing the MA2 to my canoe which was being very gently pushed by waves. MA2 was flying few meters (perhaps 1.5 to 2) over water and I was trying to get it over the canoe, lower it and catch it (as I mentioned, I mastered this with Spark with no issues).
Here, you will notice, that MA2 makes quite sudden roll adjustments without any input from my sticks. This is not caused by wind - there is no wind. It may only be caused by waves moving beneath AC and AC firmware thinking that AC is drifting away and suddenly adjusting its position.
This makes directing and catching the drone quite difficult. It seemed as it was playing "catch me if you can" with me.

Spark was much better in this regard (perhaps because its sensors were less sensitive).

This is quite important usability issue. As a pilot, I should have full control of my drone and not be second guessed by its software making wrong decisions for me.

The easy fix would be for DJI to allow switching off the downward facing sensors. The same way they allow to switch off front and back sensors. Yes - you could display a warning but, after this experinece, I strongly believe that such feature is necessary for people using this drone in a bit less common scenarios.

Mirek


2020-7-6
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GaryDoug
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See this topic. I wonder if it is about being programmed to avoid anything that looks like a water landing at all costs.
https://forum.dji.com/forum.php?mod=viewthread&tid=218743
2020-7-6
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Rustic17
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I'm thinking out of the box here...brainstorming without any regard to science...what would happen if you put opaque tape over the down sensors???  Would it even let you fly???
2020-7-6
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GaryDoug
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Rustic17 Posted at 7-6 19:11
I'm thinking out of the box here...brainstorming without any regard to science...what would happen if you put opaque tape over the down sensors???  Would it even let you fly???

I think it would not stop you flying. I flew a bit a few nights ago with almost no light in the area and nothing stopped me despite the warnings. Landed ok too thanks to the light on the bottom, which was only turned on for landing.

On second thought, maybe there are IR sensors on this one. I know the Mini has them.

Nevermind, the IR transmitters are very bright on the bottom of this one too. I just tested it outside with my IR security cameras and they lit up extremely brightly.

2020-7-6
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Labroides
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GaryDoug Posted at 7-6 19:00
See this topic. I wonder if it is about being programmed to avoid anything that looks like a water landing at all costs.
https://forum.dji.com/forum.php?mod=viewthread&tid=218743

See this topic. I wonder if it is about being programmed to avoid anything that looks like a water landing at all costs.
Except that for the times he identified,  there was no joystick input to bring the drone lower and teh drone was just hovering.
The drone wasn't trying to avoid the water, it was trying to "lock on" to the surface texture below, and not having much luck.
Page 17 of the manual explains this:
The Vision Systems cannot work properly over surfaces that do not have clear pattern variations.
The Vision Systems cannot work properly in any of the following situations. Operate the aircraft cautiously
  a. Flying over monochrome surfaces (e.g., pure black, pure white, pure green).
  b. Flying over highly reflective surfaces.c. Flying over water or transparent surfaces.
  d. Flying over moving surfaces or objects.

Having an automated system that can't be turned off is the issue.
2020-7-6
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JJB*
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Hi Mirek,

Good you did not loose your MA2 due to this difficult cano hand-catch landing!

Agree, there should be an option in the app to disable the bottom height sensor. This option with a warning message ofcourse, so users know that there is a risk for disabling.

This sensor did not always measured the distance drone>surface, see the missing values in the line.
Move heading red lines showing the actual moves of your drone, heading drone is steady.

cheers
JJB
analysis1.png
2020-7-7
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DJI Co-Pilot
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1.5 - 2m are too close above the water. Light on a water surface makes it strongly reflective and influences the vision sensors of the aircraft which leads to an unstable flight.
2020-7-7
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Mirek L
First Officer
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Canada
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DJI Co-Pilot Posted at 7-7 01:37
1.5 - 2m are too close above the water. Light on a water surface makes it strongly reflective and influences the vision sensors of the aircraft which leads to an unstable flight.

DJI Co-Pilot,

Of course what you are saying is right.

My point was different. We fly above water and we land in moving vessels above water. Spark, with its less sensitive sensors was able to handle it. MA2 struggles.

I know exactly why MA2 is unstable (which I described in my post above) and I am pointing out to DJI that providing us with an option to turn off downward facing sensors is required. In my opinion, in their quest to improve sensitivity of the aircraft (over what was available in much less sophisticated Spark) they inadvertently worsened MA2 behaviour over moving water.

Mirek

2020-7-7
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Mirek L
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Rustic17 Posted at 7-6 19:11
I'm thinking out of the box here...brainstorming without any regard to science...what would happen if you put opaque tape over the down sensors???  Would it even let you fly???

Rustic17,

Blinding downward facing sensors does not seem like a good idea.
We had discussions and cases on this forum before where obstruction of downward facing sensors caused near fly-aways.
When MA2 sees dark below while its camera and other sensors show it is a day, it assumes that it is too close to the ground and starts raising up.
I remember a case from few weeks ago, were problem with downward sensors caused MA2 to fly up and up while the pilot was struggling to force it down.

The problem is that sensor input and software instructions go hand in hand. If sensor input shows black, software says - fly up becasue you are going to hit the ground.

I believe the only sensible way to deal with this situation is for DJI to provide an option to disable downward facing sensors. I do not expect them to improve their sensing technology to recognize that it is moving water and not moving ground. Not in this price range anyways.

Mirek
2020-7-7
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Mirek L
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Canada
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Labroides Posted at 7-6 22:32
See this topic. I wonder if it is about being programmed to avoid anything that looks like a water landing at all costs.
Except that for the times he identified,  there was no joystick input to bring the drone lower and teh drone was just hovering.
The drone wasn't trying to avoid the water, it was trying to "lock on" to the surface texture below, and not having much luck.

Labroides,

Yes - you are absolutely correct.

I do not blame DJI for this at all. They did their best and the behaviour I described is caused by MA2 mistaking moving water and water reflections with moving ground and trying to stay put. DJI increased sensitivity and improved algorithms over what they had in Spark which, unfortunately in situations like I described, make situation that much more problematic.

If their sensors cannot reliably distinguish between water reflections and moving water and moving ground (which I do not expect in this price range) DJI should give pilots in more advanced situations like this, an ability to turn off downward facing sensors and rely 100% on stick input and GPS.

I remember the days when my only problem flying Spark above water was to watch it and react when it wanted to go for a sudden swim. Spark's sensors could miscalculate height above water and cause it to rapidly change altitude (it was very rare but it did happen) but I never saw Spark erratically adjusting its horizontal position because it felt woozy by water movement below.

Perhaps DJI did improve AC ability not to dunk in water - I have not seen any forum articles on MA2 going for a sudden swim because it confused its height above water. And we all have seen the video where a pilot was trying, unsuccessfully, to land on water and could not. This is good. But it created other issues described by me.

Mirek
2020-7-7
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Mirek L
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Canada
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JJB* Posted at 7-7 00:17
Hi Mirek,

Good you did not loose your MA2 due to this difficult cano hand-catch landing!

JJB,

Thanks for your graphs.

I am wondering about missing VPS data. Perhaps it is a good thing and an improvement? Perhaps, when MA2 is confused enough with water reflections, it simply stops measuring height to avoid mistakes and suddenly dunking into water? Perhaps it is a sign of "I am confused, cannot visually measure height accurately, so I will stop it and try to not go up or down without input from sticks"? The measurement returns moments later when MA2 is certain enough that it can measure the distance between itself and water.

Of course the above are mere speculations but, if I were a software developer for MA2, I would have certainly considered doing something like this and warn the pilot if the situation does not rectify itself for a few seconds or so.

Now, if this is really what is happening and how it was designed, we could apply similar logic to horizontal movements and turn off horizontal adjustments (for very short periods of time) when situation is unclear and dynamic (water reflections). Of course, this is asking for much more sophisticated software algorithms. The easy solution is - allow pilots to turn off downward facing sensors, warn them when they do and reset to a default (sensors on) for the next flight.

Mirek
2020-7-7
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JJB*
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Mirek L Posted at 7-7 06:55
JJB,

Thanks for your graphs.

Hi Mirek,

Seen few cases where MA2 hovering low above moving water dunked into to river due to yes/no vps height measuring values.

DJI did their best to stabilize their craft  using GPS and assistent by the vision sensors when within their range, normally software does a great job!

But not always, that`s why so many cautions in the manual.

So this leaves DJI only one option for some users, disable this downward sensor (advanced fly mode?)  and let the user  decide if and when this mode is used. (+ default after power on drone = enabled).
BTW same for the forcelanding, fly at 0.5 meter with speed and try to lower craft (>80% down stick) , after short moment it will autoland!!
This also when VPS sensor is measuring 0.5 meter flying high altitude.
DJI should change this also in their sw, no one wants to land their craft flying with 8 m/s forward speed.


cheers
JJB


2020-7-7
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DJI Paladin
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Hi. I am sorry for the trouble this has caused. With regards to this concern. First, the Vision Positioning System is a safety feature of the drone which helps stabilize the drone during flight it is not advisable to disable this feature for safety reasons. Second, please fly with caution above bodies of water the reflective surface may affect the performance of the drone during flight. Please refer to the image posted below the more information about the Vision Positioning System. Thank you.



DJI MA2 VPS.JPG
2020-7-8
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JJB*
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DJI Paladin Posted at 7-8 20:49
Hi. I am sorry for the trouble this has caused. With regards to this concern. First, the Vision Positioning System is a safety feature of the drone which helps stabilize the drone during flight it is not advisable to disable this feature for safety reasons. Second, please fly with caution above bodies of water the reflective surface may affect the performance of the drone during flight. Please refer to the image posted below the more information about the Vision Positioning System. Thank you.

Hi Paladin,

Not sure if what is in the manual is the whole truth.

Flying low with enough and good satelittes reception and within reach of the downward sensor, the downward vision system works as an aid to the GPS stability. That`s why drones are acting funny flying low above water when the downward vision sensor is measuring yes / no values.

If your statement is correct than, in this flight post #1, drone would not drifted and move away ; enough light + GPS oke = stabilized flight!  

I live in a country with lots of waterways, flying low over moving water is tricky  cause the vision sensor does not always measures correct ( i have read and understand all cautions ] + moving water disturbs the hover accurancy as that info software-wise indicates that the craft is 'moving'....if hover stability is only depending on GPS data than this behaviour is not seen.

cheers
JJB
2020-7-8
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DJI Paladin
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JJB* Posted at 7-8 22:55
Hi Paladin,

Not sure if what is in the manual is the whole truth.

Hi. Thank you for the additional information and your personal insights regarding the manual. I will forward this detail to our designated DJI support team for further evaluation. Thank you.
2020-7-9
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fansee45372e
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Be super careful flying low on reflective water surfaces, I was flying over a river with a lot of trees along the banks. My MAV2 was constantly making roll corrections which put it dangerously close to getting caught in the trees. I immediately found a clearing and adjusted my altitude.
2020-7-10
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Mirek L
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Canada
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fansee45372e Posted at 7-10 07:44
Be super careful flying low on reflective water surfaces, I was flying over a river with a lot of trees along the banks. My MAV2 was constantly making roll corrections which put it dangerously close to getting caught in the trees. I immediately found a clearing and adjusted my altitude.

Yes - it was these roll corrections which contributed to my troubles with catching my MA2 while being in a moving canoe.

I asked DJI to consider disabling downward facing sensors as an option.

Mirek
2020-7-10
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joesadelin
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Pakistan
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Something about water spooks a lot of flyers.
Most of my flying is over the ocean and back in the Phantom 3 days, all drones had only a single compass and IMU.

It made no difference then and it shouldn't now.
2022-3-20
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Yaros1
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joesadelin Posted at 3-20 23:30
Something about water spooks a lot of flyers.
Most of my flying is over the ocean and back in the Phantom 3 days, all drones had only a single compass and IMU.

When flying over water higher than 8 meters everything is fine, but with the new drones, they have the cheaper IR sensor, that isn't very accurate above water. Phantoms have ultrasonic sensor which make it more stable over water on low altitudes. For me, the issues happen only when hovering, I flew over water pretty low but was constantly moving, and no issues.
2022-3-20
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