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Is it ok to cancel drone initiated low battery RTH

Gizmo6257

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Faster you fly the faster you burn your battery up. Not a good idea at all.
As a general rule if I I have VLOS and the Battery is low , will cancel RTH and fly back, however if VLOS is sketchy will allow RTH to do its magic until clear VLOS has returned and than cancel RTH.

Low battery for beginners is scary: RTH gives you the confidence that your Drone can even make it back .

In order to cancel the RTH with low battery and you have to be confident that your Orientation is correct , you have to be able to see the Screen clearly and if there is Glaring Sun on you screen it can really alter that confidence.

For me RTH is giving me the Quickest Orientation possible and low battery is the signal for me to cancel it and Speed on back in linear fashion.

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Gizmo6257

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Faster you go, the higher rpm the motors go, and use more battery.
As I posted on that thread:

One certainly should not ignore the smart RTH function but, as @Meta4 pointed out, if the aircraft has enough reserve to return home under FC control then it obviously has enough to return under pilot control. He is also correct in pointing out that flight efficiency peaks at a higher speed than the default RTH speed and so, in general, you can do better than auto RTH, especially if you don't need to ascend to the preset RTH height.
 

Meta4

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Faster you go, the higher rpm the motors go, and use more battery.
If it was that simple, the slower you fly, the better mileage you would get.
But that's obviously not the case.
Your drone burns battery just to stay in the air at any speed.
There is a "sweet spot" between slowest and fastest where you will get the most miles per battery.
That sweet spot is just a whisker below top speed in P-GPS mode with obstacle avoidance disabled.
It's close enough to max speed in P-GPS, that the difference doesn't matter.
 

sar104

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Faster you go, the higher rpm the motors go, and use more battery.
That's almost, but not quite, correct if you are referring to airspeed and considering the rate of battery depletion with time. Firstly, you are talking about airspeed, not groundspeed and, secondly, what's under discussion here is the rate of battery depletion with distance - i.e. maximizing ground miles per battery. But also you are ignoring aerodynamic lift, which is not negligible. According to DJI specifications, maximum flight time is achieved at an airspeed of 25 km/hr (15.5 mph), not hovering.

Obviously it's not as simple as slower is better, because stationary (groundspeed) is zero ground miles per battery. Stationary (airspeed) is undefined in terms of ground miles per battery.

So the relationship between speed and economy, i.e. ground miles per battery (similar to miles per gallon in a vehicle) is complex but, in still air, there will be a maximum economy at an airspeed greater than zero and in fact greater than 25 km/hr if we accept DJI specs. Whether that maximum is achievable, i.e. below the top airspeed of the aircraft, depends on the form of the drag equation.

Adding a non-zero windspeed complicates things further, depending on whether you are trying to go upwind or downwind. Economy downwind with high enough windspeed is going to be maximized by flying downwind at 25 km/hr. Flying upwind clearly requires flying with an airspeed greater than the windspeed, and will be maximized somewhere between 25 km/hr and the top airspeed of the aircraft.
 
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sar104

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Not from what I've read. Sport mode drains batteries fast.
Again - you are talking about depletion rate per unit time, not per unit distance. Those are fundamentally completely different.
 

Bledsoe1qb

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No!!!!! Don't do it I did last month ended up crashing $400 repair. Fix a Crash in california is awesome
 

plangereis

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As a general rule if I I have VLOS and the Battery is low , will cancel RTH and fly back, however if VLOS is sketchy will allow RTH to do its magic until clear VLOS has returned and than cancel RTH.

Low battery for beginners is scary: RTH gives you the confidence that your Drone can even make it back .

In order to cancel the RTH with low battery and you have to be confident that your Orientation is correct , you have to be able to see the Screen clearly and if there is Glaring Sun on you screen it can really alter that confidence.

For me RTH is giving me the Quickest Orientation possible and low battery is the signal for me to cancel it and Speed on back in linear fashion.

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I totally agree with your logic on this topic. I have flown near bridges, keeping vlos, and battery levels were low. If I allowed my drone to use rth, which is set to 200 feet, it would have undoubtedly crashed into one of the bridge columns. If vlos is a bit sketchy, or I am a bit disoriented because there are no real identifiable landmarks to get my bearings, I will use rth function until I get vlos, and then cancel and fly directly back in a straight path.
 

grullonm

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As requested by a poster in this thread return home mode., I'll ask the question that's being debated: Is it OK to cancel drone-initiated low battery RTH and bring your aircraft back to land it manually?

Please explain your reasoning either way.
I agree that is okay
Recently was flying over the ocean and the Drone shows High win what's affecting the Drone. I activated RH and when drone reached the set altitude (100m my case) got message that battery was not enough to RH. Got scared as drone was away over water. I took control and set altitude to 20m where wind was mild and returned home safe with 15% battery
 

STKNRUD

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I don't think you have to worry about how drag changes with airspeed - this is just an issue that the aircraft has a maximum airspeed



That's correct. Using some simplifying assumptions one can explore that relationship further. Assuming that the power required to stay airborne is fixed (~ 130 W for a Mavic 2), that drag goes with the square of the airspeed, and that the drag coefficient for the M2 is 0.025, the energy usage per unit distance, as a function of windspeed (headwind) and airspeed can be calculated analytically:

View attachment 79935

The curves show minima, as expected, that increase with increasing windspeed. Differentiating with respect to airspeed to get the location of those minima:

View attachment 79936

So for zero headwind, that indicates an optimum airspeed of 13.8 m/s (31 mph) to maximize flight distance as a function of energy usage. As the headwind increases the optimum airspeed also increases. 21 m/s (46 mph) is around the maximum airspeed of the M2, and so that suggests that it will struggle into a headwind of greater than 10 m/s (22 mph). We know it can go into greater headwinds than that however, indicating that the assumptions are not completely correct. However, the basic trend is correct.
I am having trouble with this. Optimum cruise speed is s function of power used and distance achieved regardless of wind conditions. If your trying to get the maximum remaining distance available given the remaining fuel, you use that speed so long as your speed is greater than the headwind. Obviously if the headwind is greater than that optimum speed, your not going to move across the ground and more power/fuel is going to be needed to get as close as possible to your desired destination. But I have never heard anyone tell me to increase the power above best cruise speed if there is a headwind in order to optimize distance traveled with remaining fuel. You would only travel quicker over a lesser total distance.
 

awsan5

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As requested by a poster in this thread return home mode., I'll ask the question that's being debated: Is it OK to cancel drone-initiated low battery RTH and bring your aircraft back to land it manually?

Please explain your reasoning either way.
On your head be it
 

bartjes

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As requested by a poster in this thread return home mode., I'll ask the question that's being debated: Is it OK to cancel drone-initiated low battery RTH and bring your aircraft back to land it manually?

Please explain your reasoning either way.
It depends on de circumstances like wind, RTH altitude versus objects in the flight path exceeding that altitude. If the homepoint is dynamic, the actual landingspot may have obstacles. Last July, I also had a case of failing to return to home since I was filming the sunrise and the drone had to fly in the direction of the sun which was one big unavoidable object for it. (
)
It requires switching off the sensors before it decided to come home. Flying it backward toward me would also have helped (not Mavic Pro 2).

If you feel confident, of course you can bring it back in yourself, get some practice in flying it manual.
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. When you feel your drone can't make the return run, try to land it in a safe spot where you can hike / drive to to fetch it. At least 90% of the battery is spent by the motors so it can keep on for some time after landing with a low battery, helping you find it.
Good luck ! Bart
 

sar104

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I am having trouble with this. Optimum cruise speed is s function of power used and distance achieved regardless of wind conditions. If your trying to get the maximum remaining distance available given the remaining fuel, you use that speed so long as your speed is greater than the headwind. Obviously if the headwind is greater than that optimum speed, your not going to move across the ground and more power/fuel is going to be needed to get as close as possible to your desired destination. But I have never heard anyone tell me to increase the power above best cruise speed if there is a headwind in order to optimize distance traveled with remaining fuel. You would only travel quicker over a lesser total distance.
The fact that no one has ever told you to do that (have you ever asked?) doesn't change basic physics. So you think that the optimum airspeed into a headwind doesn't change until the wind speed becomes equal to that optimum airspeed and the ground speed becomes zero? Then what happens - the optimum airspeed discontinuously increases? By how much?

Anyway - if that's what you mean then that's obviously incorrect, since the ground speed goes linearly to zero as the windspeed increases, so the suggestion that you should just go slower and slower as the wind speed increases and only change airspeed when you come to a stop makes no sense. The calculations shown in post #18 show how the resulting smooth function describing optimum airspeed varies with windspeed.
 

jmt

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I mostly fly in the mountains and use RTH a great deal, usually when it kicks in to give me enough power to get home.

One thing that's not been mentioned so far is that you don't need to cancel RTH to modify your altitude as the aircraft is coming back. As the RTH proceeds I normally reduce height quickly to minimise problems with high altitude winds on the return and to keep my height above ground level within legal limits as the terrain falls away beneath me.

Gimbal elevation is also available for manual control in RTH mode which, together with manual altitude adjustment, allows for some nice ground hugging approach shots even though the aircraft is still in RTH mode and will land itself neatly (mostly) when the time comes.
 

JSM

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Just a tip, in RTH you can still increase the speed of the craft by pushing full stick forward, its not Sports mode pace, some where in between RTH and Sports Mode!
 
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