Strange behavior over water

[keith00]

I was in the woods yesterday trying to film a small waterfall. The trees are fully leafed out and I was down in a stream bed, but I had 8-11 satellites the entire time I was flying according to the logs. I was going to be flying over a small pool of water at the bottom of the waterfall, so I turned off the Landing Protection. I then hand-launched the Mavic from a height of about 6 feet. I flew the Mavic over the water in order to line it up with the waterfall, switched it to Tripod mode, and then tried to lower the Mavic to about three feet to begin filming. But when I pushed the stick down, it lowered a few inches and then raised up pretty quickly. I quickly countered by lowering it more, which stopped it from rising. I then tried to lower it again but got the same results. I decided I would catch it and try to figure out what was going on. When I pulled back on the right stick to back up so I could catch it, it again shot up a couple of feet.

I turned Tripod mode off and lowered it just enough to catch it, and then turned off the motors.

So, why was it doing that? I came home and tried to re-create the behavior, but I couldn't get it to do the same thing. If I turned off the Vision Positioning, it would give the same erratic behavior at home, but I had the Vision Positioning turned on while at the water. The only thing I had disabled was the Landing Protection.

It was my understanding that you only need to disable Landing Protection over water. Is that not correct?

Does the Vision Positioning still use the downward sensors when landing protection is turned off and get messed up by the water reflection? Is there a good way to mitigate that?

Thanks!

 

[msinger]

Does the Vision Positioning still use the downward sensors when landing protection is turned off and get messed up by the water reflection?

Turning off Landing Protection does not disable the downward sensors. It's usually best to disable the downward sensors when flying that close to the surface of the water.




Some guidance from the Mavic manual:

 

[keith00]

That makes sense. I've read lots of posts talking about flying over water, and I thought I had it figured out, but I guess I didn't. I guess turning off the landing protection keeps it from getting confused and "landing" too early when descending over water, but it's still using the downward vision sensors to steady itself, and those can be confused by the water reflections. I'm not sure I would totally trust myself that close to water with all of the vision sensors turned off, so maybe this is a shot I'm not ready to do just yet.

Thanks!

 

[msinger]

I'm not sure I would totally trust myself that close to water with all of the vision sensors turned off

That seems kind of backward. You shouldn't trust your Mavic with the downward sensors enabled when flying close to the surface of water. When flying that close to the surface of any obstacle, it's best to watch very closely with your eyes and adjust the sticks accordingly.

 

[Gary cato]

That makes sense. I've read lots of posts talking about flying over water, and I thought I had it figured out, but I guess I didn't. I guess turning off the landing protection keeps it from getting confused and "landing" too early when descending over water, but it's still using the downward vision sensors to steady itself, and those can be confused by the water reflections. I'm not sure I would totally trust myself that close to water with all of the vision sensors turned off, so maybe this is a shot I'm not ready to do just yet.

Thanks!

Take it slow from up high and just bring her down very very gently over the water, she will move around a little so do not get too nervous, here is what i dio when i do want to get close down to the surface and only ever in close VLOS as @msinger says.

try to get her up to at least 10 feet or 15 feet above the water minimum, then very slowly just ease her down and stop every foot or two let her hover and stabilise. then another foot or two and let her stabilise.

keep a watch and how she ascends/desends sometimes she will mover around a little, especially in wind, once you have a gauge of is she is rock steady or not then you know what room you have to play with.

dont make any sharp sudden movements that low keep it slow steady and tripod mode is not always better as sometimes u need to ascend quite qiuckly if you get into an uncomfortable situation. Once again as Msinger stated stick input is key.

i eventually got comfortable after one battery at staying at 3 to feet 5 above a fairly calm sea for long periods.

edited to say i got bored after that and decided to race Mavic against speed boats and jet skis (sports mode kept up with them all, NEVER use sports mode less than 30 feet above the sea and never at full stick unless its 60 feet).

 

[keith00]

That seems kind of backward. You shouldn't trust your Mavic with the downward sensors enabled when flying close to the surface of water. When flying that close to the surface of any obstacle, it's best to watch very closely with your eyes and adjust the sticks accordingly.

I'm sure I can trust myself to fly it without the vision sensors on, but I don't think I can fly it and film at the same time that close to the water. Without the vision sensors, my Mavic moves up and down quite a bit. If I were just 2 or 3 feet off of the water I couldn't afford to look at the phone to see what the camera sees without risking some downward drifting into the water. Maybe with a spotter I could handle it. But I was trying to move the gimbal while also flying forward, and I don't think I could handle that if I also had to worry about it drifting into the water while I was looking at the phone screen.

I'm very cautious, though, making sure I understand the behavior before I try something new with this. This was the first time trying it in these conditions, so I'm sure I'll get more confident with it once I've had some practice without the vision sensors.

 

[keith00]

Take it slow from up high and just bring her down very very gently over the water, she will move around a little so do not get too nervous, here is what i dio when i do want to get close down to the surface and only ever in close VLOS as @msinger says.

try to get her up to at least 10 feet or 15 feet above the water minimum, then very slowly just ease her down and stop every foot or two let her hover and stabilise. then another foot or two and let her stabilise.

keep a watch and how she ascends/desends sometimes she will mover around a little, especially in wind, once you have a gauge of is she is rock steady or not then you know what room you have to play with.

dont make any sharp sudden movements that low keep it slow steady and tripod mode is not always better as sometimes u need to ascend quite qiuckly if you get into an uncomfortable situation. Once again as Msinger stated stick input is key.

That's great advice. Thanks.

I just have to get more comfortable with those conditions. Up until now, I've been doing all of my flying in big, open fields, so now I just need to learn the behavior for the different conditions.

 

[Michael Ainsworth]

If you upgrade to a tablet/iPad then it's easier to control from the bigger screen.

 

[msinger]

If I were just 2 or 3 feet off of the water I couldn't afford to look at the phone to see what the camera sees without risking some downward drifting into the water.

Right on. The same thing could happen if you let the Mavic's automated system drive the Mavic when it's receiving bad data from the downward sensors. Flying that close to the surface of water is going to be risky no matter how you do it and/or which settings you configure in DJI GO.