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Is it ok to cancel drone initiated low battery RTH

bartjes

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Where did you find this gem of information?
I have used an unbalanced battery (one my drone refuses to fly with) as a power bank and I also have been trying to revive it by letting the drone drain it whilst just on the ground. After draining a full charge did not revive it though. At 8% it shuts down
 

JSM

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I have used an unbalanced battery (one my drone refuses to fly with) as a power bank and I also have been trying to revive it by letting the drone drain it whilst just on the ground. After draining a full charge did not revive it though. At 8% it shuts down
Very strange, never come across this with the Platinum or Pro 2, can run down to nearly 0% (override landing with stick up / forward) so not sure whats going on here?
 

sar104

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I have used an unbalanced battery (one my drone refuses to fly with) as a power bank and I also have been trying to revive it by letting the drone drain it whilst just on the ground. After draining a full charge did not revive it though. At 8% it shuts down
That maybe due to the problems with that particular battery - they don't normally shut down at 8%.
 

Hawkwind

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@Mr. Salty
I almost ALWAYS cancel RTH and fly back manually. This is my SOP. A great aid to getting you back home is to note the green line on your map for your RTH straight line. You can use this line and guide your aircraft back to home without any delays in determining your aircraft's orientation (which is also indicated at your aircraft position).

With my Spark, I can go MUCH further in sports mode even though it is consuming more power (but I'm also covering more ground). I haven't compared this difference with actual flights with my MP, but I would expect you can cover a lot more ground in sports mode. If you are avoiding the RTH altitude climb and decscent (if you don't need it) that will help also.

But of course, your mileage may vary. :)
 

GadgetGuy

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I have used an unbalanced battery (one my drone refuses to fly with) as a power bank and I also have been trying to revive it by letting the drone drain it whilst just on the ground. After draining a full charge did not revive it though. At 8% it shuts down
Here is your original post,
"The Mavic 1 battery shuts off at 8% so if the drone has not yet landed at that point it will fall from the sky."
It's a completely speculative statement about a single, clearly defective M1 battery, turned into a blanket FALSE statement about all Mavic 1 batteries shutting off in the air at 8%! The original statement is clearly completely false.

Any DJI battery with unbalanced cells will trigger an emergency response when any one cell voltage drops below 3.0V. Your drone is smart enough to refuse to fly with such a battery with grossly unbalanced cells. In flight, the Mavic 2 battery never shuts off until well below 2.5V on the lowest cell, which does not take place until at least two minutes of flight after it has already reached 0% remaining, at around 3.62V per cell. Fully charging your batteries before flight rebalances all cells, but not on clearly defective batteries! Never fly with a battery with unbalanced cells. Always top off the battery to a full charge before flight, if it has been stored for anything close to your specified storage mode setting, which defaults to 10 days on the M2.
 

Drgnfli

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depending on the wind direction but just for the sake of this thread, then if you have VLOS and are trying to get back directly into the wind
apart from reducing height you could use the same method as a sail boat uses and tack across the wind to make better progress
this would lessen the forces being applied to the drone to some extent, and of course would be dependant on terrain and amount of battery remaining
What? That is not a "sailboat" up there! No way can you "tack" a drone & save on battery...
 

Drgnfli

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A sail boat does not make better progress by tacking. What tacking does is, it allows the sail boat to make forward progress when sailing into a head wind. The closer to the wind you sail, the less time it will take to get from point A to B. However too close to the wind and you chance the occasional luff, due to being too close to the head wind. Also tacking is not going to make it less time because you are covering a greater distance by constantly tacking. If you have to sail into a wind, the ONLY way you will be able to do this IS by tacking because a sail boat by design, can not sail directly into a head wind, it MUST sail at an angle towards the wind, deflecting it off its sail and thereby propelling itself forward, moving left and right into the direction of the wind, over a period of time.

As for flying back to home, if you think of the drone letting out a long string behind it as it goes about flying home. A straight A to B will be the shortest route and the shortest time. A zig-zagging A to B to C to D to E to F for example, will let out a lot of string behind the drone and when you lay those two piece out straight, you will see the length you flew in the zig-zag or tacking route is far, far greater than the straight line A to B route and obviously the time to travel that distance is longer than the shortest, straight A to B route.

Therefore, tacking (zig-zagging) with a drone is not something you want to do when trying to get home the quickest and tacking in a sail boat is not the quickest way either to get from A to B, it is simply done out of necessity. If you have a headwind to fly against, then simply drop to as low an altitude as safely possible to diminish that head wind component. In general, the wind is always at a lower speed, the closer to the ground you get.
You said it better than I did - I just stated a fact... LOL!
 

DanMan32

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There's no default days to discharge on an M2. It's fixed at 10 days.
Well, I suppose it's a default if you manually discharge it after fewer days. ;)
 

GadgetGuy

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There's no default days to discharge on an M2. It's fixed at 10 days.
Well, I suppose it's a default if you manually discharge it after fewer days. ;)
Correct. I'm sure that fixed 10 days was to prevent flying on a partial discharge to storage mode, with unbalanced cells, within 10 days, which is what was happening when people selected 3 days, and didn't recharge before flight. Unbalanced cells showing a high remaining battery percentage are the kiss of death under load!
 

dannybgoode

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I cancel battery low RTH from time to time. It is by design fairly conservative so sometimes I’ll spend an extra couple of minutes pootling around.

Very much depends on circumstance though. Yesterday I was put flying over the mountains and the sea of Cyprus so I was heading home way before I was close to forced RTH - not the time nor place to take risks.

If I’m in an area I’m familiar with or it’s clear the drone would be recoverable if it landed short then I’ll cancel the rth and bring her home on manual.

I think it’s important to understand how your drone responds in certain situations, low battery being one of them, and to learn how to beat react in any given scenario and practice every so often.

Of course I fully accept the increased risk I am sometimes taking and for me it’s all about overall situational awareness.
 

dannybgoode

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Agreed - it would not be that difficult to incorporate the wind speed and direction, since the aircraft calculates those anyway.

Does the flight controller calculate wind speed as such or just respond to gusts dynamically and adjust motor rpm to maintain the current flight status without actually working out the wind speed per se. It is simply responding to a force acting on the craft.

The reason I ask is that as far as I understand it Airdata uses algorithms to calculate wind speed based on the aircraft’s angle of attack and velocity but it does this in software and does not read this data from the flight log.

I guess the other reason for not using wind speed could be that this could vary quite considerably during a flight back and may well have changed from the outward leg. It could therefore be a) inaccurate and b) the battery required could be constantly changing. At one point it might show battery critical but then the gusts drop and it shows plenty of power remaining.

Worse still it may show plenty of power remaining but then the craft clears say some trees and is no longer shielded from the wind and in fact you don’t have nearly enough power to get home. Perhaps better therefore to have a known, consistent measure which with experience a pilot can interpret?

The RTH cutoff is conservative enough I think to account for the kinds of winds people *should* be flying in and if they are flying in high winds then they should also have the experience to know they should head back with plenty in the tank.
 

Meta4

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I guess the other reason for not using wind speed could be that this could vary quite considerably during a flight back and may well have changed from the outward leg. It could therefore be a) inaccurate and b) the battery required could be constantly changing. At one point it might show battery critical but then the gusts drop and it shows plenty of power remaining.

Worse still it may show plenty of power remaining but then the craft clears say some trees and is no longer shielded from the wind and in fact you don’t have nearly enough power to get home. Perhaps better therefore to have a known, consistent measure which with experience a pilot can interpret?
The battery level does not vary significantly when flying in a varying speed wind.
It just shows how much is "left in the tank", the same way your car's fuel gauge doesn't give confusing readings when you accelerate and slow down.
The rate the amount of "fuel left in the tank" decreases will change with how hard the motors are working, just as it does in your car.
 

dannybgoode

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The battery level does not vary significantly when flying in a varying speed wind.
It just shows how much is "left in the tank", the same way your car's fuel gauge doesn't give confusing readings when you accelerate and slow down.
The rate the amount of "fuel left in the tank" decreases will change with how hard the motors are working, just as it does in your car.
I appreciate the battery level does not vary much but the distance the remaining power can take you is very much affected.

Using your analogy and applying it to a case study; when I am commuting to work - a relatively short distance in commuter traffic - with 1/4 of a tank left my trip computer shows say 60 mile before refuel. If the next journey I take is a nice motorway cruise at a steady 70mph then the distance to refuel can easily increase to 150 miles as my economy is so much better.

This is exactly the point I am making. It is perhaps unwise to have the battery low RTH to factor in wind speed as someone suggested it might as this could give an entirely false expectation of range.

As with my car I know what 1/4 of a tank left means and don’t rely on the trip computer. Just as I know that under benign flyingconditions the battery low rth can be ignored and at other tones it should be obeyed at worse as it will generally get you home in anything up to moderate winds.

EDIT: So, if the RTH low point was dynamically linked to wind speed it would be changing all the time of the inward leg, perhaps to the point of being worthless.
 

sar104

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Does the flight controller calculate wind speed as such or just respond to gusts dynamically and adjust motor rpm to maintain the current flight status without actually working out the wind speed per se. It is simply responding to a force acting on the craft.

The reason I ask is that as far as I understand it Airdata uses algorithms to calculate wind speed based on the aircraft’s angle of attack and velocity but it does this in software and does not read this data from the flight log.

I guess the other reason for not using wind speed could be that this could vary quite considerably during a flight back and may well have changed from the outward leg. It could therefore be a) inaccurate and b) the battery required could be constantly changing. At one point it might show battery critical but then the gusts drop and it shows plenty of power remaining.

Worse still it may show plenty of power remaining but then the craft clears say some trees and is no longer shielded from the wind and in fact you don’t have nearly enough power to get home. Perhaps better therefore to have a known, consistent measure which with experience a pilot can interpret?

The RTH cutoff is conservative enough I think to account for the kinds of winds people *should* be flying in and if they are flying in high winds then they should also have the experience to know they should head back with plenty in the tank.
The Mavic 2 FC computes wind speed - those data are recorded in the DAT file.
 
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dannybgoode

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The Mavic 2 FC computes wind speed - those data are recorded in the DAT file.
Thanks for the response :). Think I’m going to have to have a dig around the dat files etc. Be interesting.
 

Meta4

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Using your analogy and applying it to a case study; when I am commuting to work - a relatively short distance in commuter traffic - with 1/4 of a tank left my trip computer shows say 60 mile before refuel. If the next journey I take is a nice motorway cruise at a steady 70mph then the distance to refuel can easily increase to 150 miles as my economy is so much better.
The battery % indicator is not like your trip computer.
It's like your car's fuel gauge.
50% is just like half a tank.
How hard you drive or fly determines how quickly you run out of fuel.
 
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dannybgoode

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The battery % indicator is not like your trip computer.
It's like your car's fuel gauge.
50% is just like half a tank.
How hard you drive or fly determines how quickly you run out of fuel.
Yes I know that. Apologies I have perhaps not explained what I’m trying to say very well.

Someone suggested that the RTH battery low trigger point could be improved by having it dynamically linked to current wind speed.

I have tried to put forward a suggestion as to why this perhaps it not the way to go. When I talk about wind speed interfering with something I am referring to the RTH battery low trigger and not the % power remaining.
 

sar104

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Yes I know that. Apologies I have perhaps not explained what I’m trying to say very well.

Someone suggested that the RTH battery low trigger point could be improved by having it dynamically linked to current wind speed.

I have tried to put forward a suggestion as to why this perhaps it not the way to go. When I talk about wind speed interfering with something I am referring to the RTH battery low trigger and not the % power remaining.
There's no doubt that the smart RTH calculation could factor in wind speed and direction. I would expect that in a future firmware version.
 

dannybgoode

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There's no doubt that the smart RTH calculation could factor in wind speed and direction. I would expect that in a future firmware version.
Would it be desirable though given the extra variables it could introduce? One minute it could calculate you need to return home *now* due to winds and then a few minutes later decide you could pootle around for another few minutes. Then a really big gust and it decides its going to suggest auto landing.

Is it not better to have a fixed, known reference than one that is constantly fluctuating on the return leg?
 

sar104

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Would it be desirable though given the extra variables it could introduce? One minute it could calculate you need to return home *now* due to winds and then a few minutes later decide you could pootle around for another few minutes. Then a really big gust and it decides its going to suggest auto landing.

Is it not better to have a fixed, known reference than one that is constantly fluctuating on the return leg?
If I were programming that functionality I would use a time-weighted and height dependent wind average so that it was not unduly affected by gusts.
 

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