Could someone please explain the "power levels are approaching the minimum to ensure a safe return" RTH of a Phantom 3 Adv?

[Deleted member 120647]

There is something about it that I am failing to understand, this is resulting in behaviour I am not expecting and that is not a good thing.

My understanding is that the drone monitors the energy left in the battery and compares that with what it 'thinks' it needs to get home safely. If it thinks it is approaching the cut off point it will give a warning that it is about to intiate an RTH and, unless stopped, do so. Let's call this the safe return process (SRP).The SRP can happen before any of the battery charge warning levels are reached.

I have been learning to fly/experimenting using a couple of P3 adv's and I have occasionally seen this warning and that is not a problem but I also have the impression that I have occasionally NOT seen this warning and have then flown 'into' the low battery warning level and continued flying expecting the drone to initiate the SRP. When it has failed to do so I have been left with the drone hitting the critical battery level threshold and telling me it is going to descend. Fortunately I bring the drone fairly close to 'home' at the low battery warning but two of these occasions have produced 'hairy' landings.

Tonight I deliberately set out to try and get an SRP and didn't.

I believe that if the drone is within 20m of the home point it will NOT attempt to RTH but simply land so I had the drone hovering at a height of about 5ft a little over 200ft away from the home point. The drone and I were in an empty grass field and it hovered quite happily into and though the low battery zone that I think I had set to 25%, when it crossed the critical battery level threshold, which I has set at 19%, it tried to land. I saw no SRP notification and I would not hear one if there is one as I am deaf. Now I admit I could have missed the warning on the screen but I don't think I did.

I am not certain if this behaviour is shown by just one of the drones I have been using or both.

So, my question is ...... do I misunderstand the SRP? IF so can someone please correct me?
What happens if the SRP is somewhere between the low battery warning level and the critical battery warning level?
Thanks

 

[solentlife]

mmm interesting.

OK - one thing to remember is that auto-RTH which should initiate when battery level is detected as minimum to get home, makes no allowance for wind / weather. This means that if it is flying INTO wind during that RTH - it will not get home , but will land out before. If its flying WITH the wind during RTH - then it will get home with a small amount to spare.
It also has to allow for climb to altitude ... descent from.

I do not think auto RTH is related to the settings we make for low and critical battery via the App. I have reason to believe that Auto RTH is based on default settings.

As to why you did not get warning ... I think is based on the default settings - not your user settings. Maybe put settings back to 30% / 10% and test again ?

But take care ... my P3S started auto-land at 14% and I could not deflect or alter its descent in any way at all ... it landed in the river and even though I recovered it - was totally shot.

 

[Deleted member 120647]

Thanks Solent, ahh it seems I had one thing wrong at least, I thought it was able to take wind into account.
Re "but take care" indeed, the behaviour during the cumpulsory landings is what made things "hairy".
Whilst it did respond to commands during this last night and I was actually able to bring it 'homish', ( I just wanted to see what I could do and what control I had) control was nowhere near as good as during normal flight.
I will see if I can have another trial today with 30% & 10% etc.


PS I forgot to ask, other than the wind thing is my understanding of the SRP correct or reasonably so?

 

[solentlife]

My understanding is that the drone monitors the energy left in the battery and compares that with what it 'thinks' it needs to get home safely. If it thinks it is approaching the cut off point it will give a warning that it is about to intiate an RTH and, unless stopped, do so. Let's call this the safe return process (SRP).The SRP can happen before any of the battery charge warning levels are reached.

In essence - yes.

If you look at your screen while flying ... you will see a line denoting battery situation ... (Page 13 of Adv manual ..)

The H in the circle that moves along the line is the point that if the Green reduces to will trigger Low Battery RTH.

You will note that the Low and Critical settings are not used in the Low Battery RTH. It is purely the STILL AIR calculation to ascend to RTH height - fly home - descend to land.

 

[Deleted member 120647]

Thanks, I will have a look.

 

[bsartist]

I believe it’s possible to turn low batt RTH off. At least I can on my P4P. May want to check that setting.