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Return to home at low battery: max battery or max distance speed?

lomposlapos

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Drone (Mavic 2 Pro) is, for example, 5 km away and drone's battery is getting "low". You want to fly back the drone to you as safely as possible. Do you use the max battery speed or max distance speed?

Max battery speed 25 km/h = 7 m/s = 15.5 mph = 13.5 kt
2.4 min/km = 0.42 km/min
Max distance speed 50 km/h = 14 m/s = 31.1 mph = 27 kt
1.2 min/km = 0.83 km/min
 
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I think if it was 5 km away with a low battery it wouldn't matter, it isn’t going to make it

Doesn't the low battery alert take into account the distance from the home point? (but not any possible winds)
 
In my opinion I think max distance is the right answer. Also, the higher speed would help fight any wind encountered.
 
the drone will start a RTH when the battery level reaches a point, that it considers the battery only has enough charge remaining, to cover the distance back to the home point it is based on distance ,and does not take wind direction into its calculations, the problems happen when the drone is unable to sustain enough forwards momentum into the wind to make it back
it is up to you the pilot ,to be aware of the batteries remaining charge, and the distance from the home point so that you will have enough battery to make it home
 
Drone is, for example, 5 km away and drone's battery is getting "low". You want to fly back the drone to you as safely as possible. Do you use the max battery speed or max distance speed?

Max battery speed 25 km/h = 7 m/s = 15.5 mph = 13.5 kt
2.4 min/km = 0.42 km/min
Max distance speed 50 km/h = 14 m/s = 31.1 mph = 27 kt
1.2 min/km = 0.83 km/min
Why are you wondering?
The numbers tell you everything you need to know already.
One speed will keep the drone in the air longer (but not cover much distance).
The other speed will go as far as possible on one battery.
If you think that staying in the air longer but not going far is the answer, say goodbye to your drone.

In case you haven't worked it out, the speed that gives the most distance per battery is what you need when distance is the priority.
 
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Definitely consider RTH altitude and wind. I say this with recent experience of higher winds aloft ruining my flight plan on July 4th. Got it back undamaged the next day.
 
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In case you haven't worked it out, the speed that gives the most distance per battery is what you need when distance is the priority.
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So you are saying, from any distance, use the max battery speed 25 km/h to bring home the drone (instead of max distance speed 50 km/h).
Would you mind to detail the science behind it?
 
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So you are saying, from any distance, use the max battery speed 25 km/h to bring home the drone (instead of max distance speed 50 km/h).
Would you mind to detail the science behind it?
Quite the opposite.
To put it in terms you might find easier ...
If you are on the highway with your fuel tank running low and concerned you might not make it all the way home .... you should drive at the speed that gives the best fuel economy.
The speed that gives the most miles per gallon will give you the best shot at getting home, from any distance.
With the drone, the speed that gives the most miles per battery would be what you want.
 
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the speed that gives the most miles per battery would be what you want.

so it is at 50 km/h is the safest speed to bring the drone home

BTW, manual says:
· Max Flight Time 31 minutes (at a consistent 25 kph, no wind) [= 12.9 km]
· Max Flight Distance 18 km (at a consistent 50 kph, no wind) [= 21.6 min]
 
This is a very useful question to know the answer to. Please do not reply with your instincts. I am interested in the answer for this as well. A year or two back, I saw a video of someone doing a range test and wasn’t able to bring back his drone. He was returning back on sport mode and every single comment was claiming him crazy for returning home on sport mode and that he would’ve made more distance with regular mode on a slower speed.
 
This is a very useful question to know the answer to. Please do not reply with your instincts. I am interested in the answer for this as well. A year or two back, I saw a video of someone doing a range test and wasn’t able to bring back his drone. He was returning back on sport mode and every single comment was claiming him crazy for returning home on sport mode and that he would’ve made more distance with regular mode on a slower speed.
@Meta4 answered it spot on above. I have the Mavic 2 Pro and often do distance flights over wide open areas of ocean. Assuming no wind, the M2P in P mode with all OA sensors turned off cruises at 31MPH - which coincidentally, coincides with DJI’s Max Distance Speed for the aircraft. I do not use or allow RTH on a regular basis, but I do test its function anytime I get a new system. With the M2P, with no wind, the low battery RTH will return the aircraft with approximately 30% battery remaining upon landing, so one needs to decide for themselves how far they want to push it after canceling that warning. I never use Sports Mode for distance flights. It is very inefficient and IMO, a gimmick. Add wind to the mix, and that’s a whole other topic. I love wind as well, very high winds, but I also have ATTI Mode available as a flight mode on my M2P, so I go outbound low into the wind and then turn and climb into the typically higher velocity winds to come home. The combo of higher velocity tailwinds and switching to ATTI Mode can attain some crazy speeds.
 
Drone (Mavic 2 Pro) is, for example, 5 km away and drone's battery is getting "low". You want to fly back the drone to you as safely as possible. Do you use the max battery speed or max distance speed?

Max battery speed 25 km/h = 7 m/s = 15.5 mph = 13.5 kt
2.4 min/km = 0.42 km/min
Max distance speed 50 km/h = 14 m/s = 31.1 mph = 27 kt
1.2 min/km = 0.83 km/min
Are these measurements has factored in wind conditions - headwind or tailwind?
 
No, they don't factor-in any windspeed or direction. Forgive me y'all but I really am struggling to see the usefulness of this thread. Real world situations require different tactics, don't you think? The wind is seldom, if ever, at zero from the ground up to 400 feet, around here anyway. And what exactly do we mean by "low", as in battery % remaining?

Reducing a 3+ dimensional problem to 2 dimensions is a good start but no basis for decision making. You've still got to contend with the other dimensions.
 
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No, they don't factor-in any windspeed or direction. Forgive me y'all but I really am struggling to see the usefulness of this thread. Real world situations require different tactics, don't you think? The wind is seldom, if ever, at zero from the ground up to 400 feet, around here anyway. And what exactly do we mean by "low", as in battery % remaining?

Reducing a 3+ dimensional problem to 2 dimensions is a good start but no basis for decision making. You've still got to contend with the other dimensions.
I took “low” to mean the Low Battery RTH warning, but let’s call “low” just enough to get back and land at 0%. I think what we can learn from this thread is don’t use Sports Mode, and just turn straight toward home and go full forward with the right stick.

Wind is certainly a variable in the real world, but if you never head outbound with a tailwind on a distance intended flight, you should never have a problem. Depending on where you fly in Upstate, NY, I suppose there could be variations in wind direction around the mountains, but this is usually not an issue.
 
There are no guarantees the wind won't turn 180 degrees from the last prediction on your forecasting app. Not to mention that the forecasting app may not have been correct in the first place.

As an SOP, launching into the wind and returning with the wind is a good one, I totally agree. But the wind does tend to shift as you clear higher terrain, happened to me quite recently. I recovered it the next day on the forest floor, slimed by disappointed slugs. That one ranks as a 'gotcha' in my invisible log book.

So, that sort of thing being the case, what is the point of this thread other than pointing out there are two possible RTH scenarios when flying in non-existent zero wind conditions? :)

If I hadn't put it in sport mode and descended rapidly I'd have never overcome the wind and gotten it to 50 feet from my driveway.
 
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