Lost Mavic 2 Pro, battery depleted 1% very 2 seconds on return to home point

[paulatkin73]

I didn't know any of that. This is really useful information. Thanks for posting this!

it is just a consequence from the law of thermodynamics - more speed means more energy, more energy from the limited source means less time.
where it gets hairy is - more speed may not mean more distance - when we go against the wind, and, together with less time - it all fails.
plus, the stock computation for RTH is built based on the windless - i think - situation based on the anticipated rate of battery consumption - what did they put into that algorithm no one knows for sure as code is not open - but - as many had a chance to see - it is pretty far from perfect.

it is easy to start dealing with it, with time, but, as i stated many times before - the best approach is to know where wind blows and do not go too far downwind as getting back may get tricky if wind gets stronger. or, make sure you have a lot of battery left.

also, an important thing to remember - old lipos deplete not like new ones, they sag and loose voltage way faster. dji code is not aware of how old your lipo is - it is done from the perspective of the brand new lipo. so, the power reserve it shows may not be the one you actually have.

 

[globetrotterdrone]

[...] it is pretty far from perfect.

I agree with you, but it's pretty usable and I guess something achievable to implement without the need of a bigger drone for more sensors etc.
On the other hand, it may intensify users' perception of how far they can go. 55 % is good enough, no need to RTH, 30 % no need etc. There are countless videos of pilots who cancel the RTH as their experience say, it's too early etc. And while no one is indeed all knowning, I got the impression that it often has to do with your personal attitude towards safety. Some need to learn it the hard way (hopefully without involving third parties).

Having all this tech wizardry does not prevent of proper preparation or knowledge of other factors as you pointed out (wind direction, some basic understanding of the elements in general).

also, an important thing to remember - old lipos deplete not like new ones, they sag and loose voltage way faster. dji code is not aware of how old your lipo is - it is done from the perspective of the brand new lipo. so, the power reserve it shows may not be the one you actually have.

Really? Of course nobody really knows, what DJI implemented with their code, but I guess, as the charging cycle etc. is being displayed, they could also have specific lines of discharge based on that. No one knows for sure, but I think it's feasible although general again.

 

[paulatkin73]

Really? Of course nobody really knows, what DJI implemented with their code, but I guess, as the charging cycle etc. is being displayed, they could also have specific lines of discharge based on that. No one knows for sure, but I think it's feasible.

when your 3400mah lipo becomes efficiently a 2400mah lipo due to overabuse - you not gonna see that, and code not going to see that. all you will see that the expected curve of the discharge - voltage level - will drop down way before it was supposed to.

same way it is why all say same thing - if you take off with not fully charged lipo - then your estimates are all off as RTH estimate goes by the computation of consumed mAh compared to anticipated stock 3400mAh. it is all approximate. that is why you always have to have cell voltage indicator on the go4 app screen and pay attention to how fast it changes and where it is.

speaking about wind - DJI did do a computation of wind direction and its speed. it is in the .DAT file data. they just for, again, due to pure idiocy of developers, did not put this data on the screen.

 

[globetrotterdrone]

@paulatkin73
I get you buddy, all I am saying ist that DJI might have some alternative lines of discharge when the batteries have more cycles/have an older manufacturer date etc. If they have, they can only be quite general as well, as we both and others know, that the sag is individually and overabuse is hard to analyse beforehand.

it is all approximate.

Indeed, Einstein and other famous and clever thinkers have shown that.

 

[paulatkin73]

@paulatkin73
I get you buddy, all I am saying ist that DJI might have some alternative lines of discharge when the batteries have more cycles/have an older manufacturer date etc. If they have...

nope, they do not have. i looked at what i was getting starting with 40% and 50% depleted batteries - they seem to do some update of the time based on the starting voltage - but - it is as correct as a shot in the dark - when you get cells to the 3.8 or 3.9v - you have no idea what factual capacity is left in there. so what i think they did - they simply adjust starting capacity based on the level of the initial voltage and keep the curve the same.

 

[Gryphon962]

I might be the last to realize this, but one big impact to long range flying is that when downwind, the drone still limits its speed to the max for the mode selected. So you don't get the benefit of the wind behind you. For example, if your drone does 41 mph still air in S mode (MP1), then it will still do 41 mph with a 15 mph wind behind it. Ouch.

 

[PhantomFandom]

I might be the last to realize this, but one big impact to long range flying is that when downwind, the drone still limits its speed to the max for the mode selected. So you don't get the benefit of the wind behind you. For example, if your drone does 41 mph still air in S mode (MP1), then it will still do 41 mph with a 15 mph wind behind it. Ouch.

I am not sure that's totally true in all cases but even so, you are still getting the benefit of the wind. If you're moving at 41 MPH with a direct tailwind of 15 MPH then the motors are only doing the work necessary to propel the drone at 26 MPH in calm air.

 

[Andrewandron]

Wow! It flew over a mile, against the wind with 0% battery indicated! That battery deserves a medal of honour for it’s courage and valiant effort. Too bad it’s likely never to be awarded it.
Sorry for your loss but it was taken out by a strong headwind. I hope you do find it.

 

[Andrewandron]

I might be the last to realize this, but one big impact to long range flying is that when downwind, the drone still limits its speed to the max for the mode selected. So you don't get the benefit of the wind behind you. For example, if your drone does 41 mph still air in S mode (MP1), then it will still do 41 mph with a 15 mph wind behind it. Ouch.

True, although you do get the benefit of it using less energy to maintain that speed. And of course the drain of energy to go against it.

 

[Stephenmaycol]

I need to check the flight log regarding wind speed etc. Battery had recently been charged. Was at 100 or 99% no less. As I said I know I'm an idiot. The rth warning is there for a very good reason. Lesson learnt there. That very interesting regarding getting better distance on P mode than on Sport mode.

I have had a battery show full charge and after a couple minutes in the air I receive a message that it is self discharging... at this point I brought it back home landed and restarted the battery. I did notice that in the few minutes of flying the battery dained 10%. I think it was an error on startup. I think the battery had entered self discharge but did NOT indicate it for several minutes.