Flying in narrow gorge, over water, with zero satellites

[Freddy K]

Hi everyone,
A few days ago, I launched my Mini 2 to try to get some shots from a waterfall. The launching spot was at the bottom of the waterfall, deep within a narrow gorge with streaming water (no wind at all). The drone was already 30m away (3m high) when I noticed that I had 0 (zero) satellites.
This makes absolute sense as there was hardly any visible sky there. And obviously my mistake for not having checked the number of satellites before liftoff.
I was flying very carefully towards the waterfall in cine mode to avoid branches when I noticed that the drone was drifting slightly and I had to continuously compensate. That's when I noticed the 0 satellites. I (slightly) panicked a little but managed to get the drone back safely.

My questions:
- When the drone has no gps lock, it flies in ATTI mode, right?
- When in ATTI mode, does it use the downward sensors for hovering in place or not? As I already said: height was +/- 3m.
- Could the fact that the drone was flying over rapidly streaming water be the cause of the drifting?
- if the downward sensors were the reason of the drifting, is there a way to "disable" them so I could have flown the drone completely manually without interference from the water below (if I'm not mistaken, the drone uses barometer readings to stay at the same height)?

Any feedback is greatly appreciated.

 

[Meta4]

- When the drone has no gps lock, it flies in ATTI mode, right?

Yes

- When in ATTI mode, does it use the downward sensors for hovering in place or not? As I already said: height was +/- 3m.
- Could the fact that the drone was flying over rapidly streaming water be the cause of the drifting

Yes, and yes.
The VPS sensors need good lighting and a definite pattern or texture to lock onto.
With moving water it can't work properly.

- if the downward sensors were the reason of the drifting, is there a way to "disable" them so I could have flown the drone completely manually without interference from the water below

DJI don't offer the option of disabling the downward sensors for any of their DJI Fly drones.

 

[Yorkshire_Pud]

To a certain extent the VPS will track an object in its field of view. I have slowly moved a box that was directly under my hovering indoors mini 2, the drone followed the box. This was not random drift, it was a definite response to the movement of the box.

You can disable the sensors, by putting tape over them.
However without out GPS you will probably have to accept/confirm-receipt-of/ok, several warnings before the drone will start its motors.
I see this ALL the time indoors and have to accept etc. the warnings, it's so routine I can't remember the wording of the warnings etc. or how many 'acceptances' I have to give.
But, in my case, as soon a the drone is airborne sufficient light reaches the 'ground' beneath the drone for the VPS to work and VPS then provides braking and position holding.

 

[ChrisOutdoors]

DJI don't offer the option of disabling the downward sensors for any of their DJI Fly drones.

I have all vision sensors disabled on my mavic, never needed them.

 

[Meta4]

I have all vision sensors disabled on my mavic, never needed them.

But your drone doesn't use DJI Fly.
Earlier drones using DJI Go 4 have a lot more settings and options.

 

[vandemonian]

The drifting was just local air currents - all air, even in an enclosed canyon is not stationary and the drone is flying in an air packet that has its own "life" (drifting) and plenty of things are acting on that packet of air to move it, including the drone itself and your drone just sits inside an almost discreet packet of air and moves because the air packet moves - maybe increasing heat or cololing, wind or small air currents, changing air pressures above and below.. all make the air move.. GPS is awesome at keeping the ship steady and maintain position.. when GPS is not available the other sensors only act when proximity limits activate so its a very course adjustment.

Go and fly your Mini in a safe place in a changing wind with good GPS and watch it or the attitude display and it will be constantly making rapid alteration of pitch and roll to fight the wind and maintain position.. without the GPS signal it would just start drifting with the packet of air until a proximity sensor activated and unless you had collision avoidance "on" or adjusted the path it would probably hit the obstacle.

Cheers,
Chris

 

[Yorkshire_Pud]

when GPS is not available the other sensors only act when proximity limits activate so its a very course adjustment.

I think that is mistaken, I think VPS works perfectly well in the absence of GPS and, when in conditions that allow it to function, it controls position etc. much more accurately than GPS.
Having flown drones, Minis 1/2 & M2P/Z, from the same place, in the same conditions, except for day vs night, the drones' position holding etc., when low, etc. is much better in daylight than in the dark. The only difference between the flights is that VPS is available during the day and not available in the dark.
I would go so far as to guess that when VPS is available it is the primary source of position holding etc. but when VPS is not available the drone reverts to GPS position holding.

Indoors with no GPS but sufficient light my Minis are horizontally cm perfect in a hover, slightly more so than the M2P/Z.
I suspect that in Freddy K's flight the VPS was either confused by the water or trying to 'track' movements of the water or foam or debris on/in the water.

 

[Zbip57]

A few days ago, I launched my Mini 2 to try to get some shots from a waterfall. The launching spot was at the bottom of the waterfall, deep within a narrow gorge with streaming water ...

Without sufficient GPS reception the drone relies on the optical sensor of the VPS to maintain horizontal position in hover whenever the control sticks are centred. If the VPS is out of range because the drone is too high, or it's too dark for the optical sensor to see anything, or the surface that it does see has no distinguishable features (it's all one colour like a snow-covered field), then the drone reverts to ATTI mode.

It's not the end of the world. It's controllable and will still respond to all your stick inputs. It just won't automatically brake to a complete stop and hold position whenever the sticks are released. It will continue coasting along and drift with the wind, unless you use your control sticks.

But you can get unexpected results when flying without GPS, like in a deep gorge, over moving water. With sticks centred in hover, the VPS optical sensor will try to hold position on any distinguishable feature it sees. If that is bubbles or ripples on moving water, the drone will track those and move downstream all by itself, rather than hovering in one spot as you intended.

That once happened to me. Same scenario. Deep gorge, insufficient GPS, moving water. I left my Mini-1 hovering low over the water and looked away for a moment to change settings on my screen, then was startled to find the drone had drifted some distance downstream all by itself. Eek!

I later had a second eeek moment, also VPS related, when I was bringing the Mini back and down from above the waterfall, intending to land back at my launch location. The Fly app suddenly announced "Landing" and the Mini proceeded to descend toward the pool of water below the falls. EEEEK! That turned out to be because the Mini was descending through the mist off the waterfall. The VPS infrared sensors detected the mist as "something" closer than 2ft beneath the drone and, because I was holding the throttle stick down at the time, it interpreted that as the command to auto-land.

See this earlier thread, and follow links from there to detailed discussion.
mavicpilots.com/threads/les-chutes-coulonge.121162/

 

[Freddy K]

Thank you all for your thoughts and explanations.
I have only been flying drones for less than a year and don't consider myself experienced enough to handle these kind of situations with confidence.
So, I'm glad I made the decision to immediately return to my launch location (and successfully doing so).
Maybe, after having flown more hours and finding myself in a similar situation again, I will feel confident enough to go ahead and navigate the drone to where I want it in ATTI mode.
I still remember the first time I launched my first drone (Tello) with a pounding heart, minutes before I flew it into the nearest tree. Confidence and experience comes with practice.

 

[Brojon]

Thank you all for your thoughts and explanations.
I have only been flying drones for less than a year and don't consider myself experienced enough to handle these kind of situations with confidence.
So, I'm glad I made the decision to immediately return to my launch location (and successfully doing so).
Maybe, after having flown more hours and finding myself in a similar situation again, I will feel confident enough to go ahead and navigate the drone to where I want it in ATTI mode.
I still remember the first time I launched my first drone (Tello) with a pounding heart, minutes before I flew it into the nearest tree. Confidence and experience comes with practice.

lol - you actually did quite well in ATTI.
My MP lost GPS when I flew under a metal bridge (wasn't thinking).
It drifted UP and nothing I did affected the vertical.
I tried lateral and it wasn't fast enough - crashed into the bridge and fell into the mud.
I completely disassembled it, cleaned it and it's still flying.
I related the tale to illustrate you did fine and survived the "encounter".