Please can anyone tell me if I must keep my vps on over water or off as I saw a video showing how it affected a mavic pro when left OFF.It nearly landed in the drink at a 2'' hover.Went up and down and sideways erractically with no wind over a still lake.

Some say off, some say on, I always leave vps on over water and have never had an issues. I primarily fly over water, sometimes as close as 3 feet above surface, in sport mode at full throttle.

Makes no difference if your drone is beyond the VPS range so if flying more than 10m above the water then it's up to you. If flying low over water (which is a risk in itself) I'd turn off VPS.

The usual story is that leaving it on when down low might be a problem.
Either your video is confused or you are.
Unless you are down within a few metres of the water it shouldn't matter.

Got a link to the video?

I say leave it on. I fly over water all the time with my P3A and MP sometimes meters
above the water without any issues.

My understanding is the VPS uses mostly visual but also a sonic method to measure the distance from the surface.  So it seems it's a combination of the two with an emphasis on the visual aspect.  But the visual aspect looks for differing texture/patterns on the surface.  Grass/gravel, etc is obviously perfect.  But water?  What texture/pattern is there?  The sonic aspect of it might work okay, but I can see why the visual aspect wouldn't work correctly.  So that would seem to indicate that we'd want to have it turned off.

OTOH, what does VPS do, exactly?  Doesn't it just help (with the aid of satellites) to hold the AC in position?  It wouldn't cause it to drop or rise, right?  The altimeter controls that.  So that would indicate it doesn't really matter.  Your VPS readout on your app might skip around, but the AC itself shouldn't be affected.

So I guess it's just a matter of personal preference.  

Strange that only one person Labroides mentions that it may not matter ...

VPS loses its effectiveness once you get more than 3m height ...  it is only really of use in that narrow height band of zero to 3m.

BUT even DJI warns that water surface ... and similar non-contrast non solid surfaces are not good for VPS and can lead to errors sent to Flight Controller .. it is recc'd to switch off VPS if you intend to fly low over water ... waving grass ... marshland etc. to avoid any errors it could lead to ...

As to the opening post saying :  " I saw a video showing how it affected a mavic pro when left OFF.It nearly landed in the drink at a 2'' hover.Went up and down and sideways erractically with no wind over a still lake. .... one I am skeptical of the 2" (inches).. should that be 2' (feet) ? And if it is 2 ft ... then it is the VPS was ON ... not OFF ... still water is exactly what they warn you about ...

I fly over water for possibly 70% of my flights ... I rarely get down to VPS height over it - so I leave VPS on .... but if I was to want to fly very low ... less than 6m above the water ... I would switch off VPS ...

Nigel

solentlife Posted at 11-4 06:12
Strange that only one person Labroides mentions that it may not matter ...

VPS loses its effectiveness once you get more than 3m height ...  it is only really of use in that narrow height band of zero to 3m.

I also wonder that with VPS turned on, the drone will act, seem more unstable when trying to land or is that more of a problem caused by the prop down wash turbulance?

Mark The Droner Posted at 11-4 05:58
My understanding is the VPS uses mostly visual but also a sonic method to measure the distance from the surface.  So it seems it's a combination of the two with an emphasis on the visual aspect.  But the visual aspect looks for differing texture/patterns on the surface.  Grass/gravel, etc is obviously perfect.  But water?  What texture/pattern is there?  The sonic aspect of it might work okay, but I can see why the visual aspect wouldn't work correctly.  So that would seem to indicate that we'd want to have it turned off.

OTOH, what does VPS do, exactly?  Doesn't it just help (with the aid of satellites) to hold the AC in position?  It wouldn't cause it to drop or rise, right?  The altimeter controls that.  So that would indicate it doesn't really matter.  Your VPS readout on your app might skip around, but the AC itself shouldn't be affected.

Hi Mark ...

We know that VPS is there primarily as an Indoor tool ... so when you are in that hall - you have a system to provide visual assistance to hover etc.

As you say - it needs contrast and also solid surface to work. Trouble is water is neither.

Why would VPS cause problems if we have satelites ? The big question indeed and simply answered by : The VPS provides input to the Flight Controller along with barometer and satelites. Combination arrives at stable hover and also altitude reading.
If the VPS is outputting varying data - as it would with water / waving grass etc. - you would have conflict in Flight Controller determining true data. At low levels - the VPS is supposed to be more accurate than barometer ... because it picks up not only sonic but also visual reference to the ground. That being so - if it says you are 10ft when hover was set at 3ft ... FC will then have to decide which is right ... barometer or VPS ... which can lead to it taking the VPS data to over-ride barometer ... model descends 7ft .... BHAM !! she's in.

OK ... I agree - that may be exaggerating the matter ... but an easy to produce example is - hover at 1 - 2m above waving grass ... and see what happens ... be ready to push left stick UP !!  The model gets unsteady in its hover quite quickly ... in fact we see it when we land ... once she gets close to the ground ... you can often get that wandering and jump ... before it sits down. Some claim its ground effect ... yes when its just the 'jump' .... but the wandering is particular to the VPS equipped machines.
I noticed it when I changed from P3S to P3P machine immediately.

Nigel

solentlife Posted at 11-4 06:36
Hi Mark ...

We know that VPS is there primarily as an Indoor tool ... so when you are in that hall - you have a system to provide visual assistance to hover etc.

Hi,

Okay I didn't realize VPS also had some control over altitude - sharing with the altimeter.  I guess that makes sense.  In that case, flying/hovering low over water, I would turn the damn thing off.  Haha  Thanks

Mark The Droner Posted at 11-4 07:32
Hi,

Okay I didn't realize VPS also had some control over altitude - sharing with the altimeter.  I guess that makes sense.  In that case, flying/hovering low over water, I would turn the damn thing off.  Haha  Thanks

Its how it was explained to me .. seemed to make sense. If you hover over waving grass with VPS and then do it without ... you see a difference.

Nigel

With the VPS turned on it probably also scares any nearby wild life and makes dogs look up and bark.

Air/America Posted at 11-4 06:23
I also wonder that with VPS turned on, the drone will act, seem more unstable when trying to land or is that more of a problem caused by the prop down wash turbulance?

Both.

Land a P3S and then a P3P .... there is a difference.

Nigel

Yes - I couldn't stand the way it lands with the VPS on.  I turned it off for that reason long ago.

You would think, when the left rc stick is pulled straight back, and the elevation is reducing, the VPS would auto shut off, on its own.

Perhaps this thought might be implemented in future firmware upgrades for the Phantom 4 series.

And any subsequent newer DJI models as well.


RedHotPoker

solentlife Posted at 11-4 08:06
Both.

Land a P3S and then a P3P .... there is a difference.

Thank you Nigel, for your advice and expertise.