Is the Smart Return to Home really Smart ?

Feb 24, 2021
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A few times now I have been trying to fly from a beach to the tip of a nearby mountain, obviously ascending in the process over a distance of approx. 3 miles. I have chosen days with no wind or with tailwind on the way back, because the land in between is a mystery to me and difficult to access and I did not want to be forced to land in that area. Unfortunately, all attempts where messed up by the Smart return to Home. Strangely enough, in DJ Go the video signal loss and the return to home where far earlier than with Litchi, but also Litchi forced me to return home and ... when I got back to the beach the battery still had 55% capacity. I wanted to try disabling the Smart Return to Home, but not even knowing how it is called (some call it RTH on low battery) I had no clue how the Phantom 3 Pro with todays actual app versions would behave with Smart RTH unchecked in case of loss of signal. I tried to fly the other way round, where the return is more consuming, and I could reach the same beach from the same mountain, but shortly after that I was forced back. Here is the flight
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and my main questions. How does the phantom behave with Smart RTH disabled in case of loss of signal. I know it has been discussed before, but usually around 2017 and with todays versions of Litchi or DJ Go it might be different ... while the firmware should have stayed the same. Furthermore, I felt blackmailed by the system when I tried to cancel the RTH, because every time I was told 'aircraft requests to go home' and canceled the procedure within 3 seconds the app would report signal loss and return to home anyway. Signal loss every time I cancel RTH and with full signal just a few seconds ago seems suspicious to me. Anybody experienced the same behavior? But mostly, can I assume that after loss of signal the Phantom 3 will always return home or try to do so no matter the settings in the app (on device or drone) ? Thanks for your help !
I don't believe it's possible to disable Failsafe RTH. Failsafe RTH happens when your drone loses signal for 3 seconds. Low Battery RTH is triggered when the battery is depleted to the point that it may affect the return of the aircraft. Smart RTH is when you hit the RTH button.

Have you tried planning the mission in advance using Litchi? The Phantom will continue after loss of signal unless there is a low battery.
I don't believe it's possible to disable Failsafe RTH. Failsafe RTH happens when your drone loses signal for 3 seconds. Low Battery RTH is triggered when the battery is depleted to the point that it may affect the return of the aircraft. Smart RTH is when you hit the RTH button.

Have you tried planning the mission in advance using Litchi? The Phantom will continue after loss of signal unless there is a low battery.
Thanks for the advice ! I did not try to fly a mission because I primarily use DJ Go and installed Litchi just for the occasion, to see if it also would 'come back' far too early. But I guess that if what happens to me is a Low Battery RTH the mission would be aborted anyway, right ? I'll give it a try ...

I am also surprised that the RTH button causes a Smart RTH, thought Smart means that he is smart enough to know where he is, how the way home is gonna be and determine based on these parameters when he needs to return because the battery is just enough to return home (with all due precautions, contingencies and policies to never plan flying with less than 30% battery or whatever).
Litchi will provide an estimated flight time based on the waypoints. Obviously, never attempt a mission that would exceed the life of your battery, maybe 18 minutes. Where people tend to make mistakes is compensating for altitude that result in losing it in the trees or severe head winds upon return that makes the thing work harder and lose power faster. If the Phantom is unable to make it home, it's going to land wherever it's at to ensure it doesn't fall out of the sky. In your case, could be a water landing.

Ya, I never understood why DJI called it Smart RTH when the pilot is doing the thinking. I think by smart they mean the Phantom knows where the to fly to get back to the home point.
Wow, there you got me ... when I fly over water I always keep the battery values on my radar and an escape route ready, every 1000 feet I check the consumption and am always ready to 'ditch' it on the beach, just in case the unforeseeable happens. Yet so far, getting to know the bird without losses. Did fly it over water on somewhat windy days, and it was ok, except you would see more of the props on the picture. Will start planning missions now and see how it behaves, hoping the planning itself will be a good school of thoughts.
There is an abundance of Litchi Mission Hub tutorials on YouTube. Plan some short missions where you never lose sight of the aircraft. Get a thorough understanding as to how it works and know how to cancel a mission mid-flight. One of my first missions returned as planned but then made a hair pin turn and was headed who knows where. I never did figure out what happened but suspect it was an error on my part when I planned the mission.
Still flying the old dji 3 and 4 apps, hopefully will never need RTH but otherwise I just come in when it’s time to come in. Nice views, Good luck
I disable smart return to home and obstacle avoidance when flying extended waypoint missions as a matter of routine. I do a lot of them as a commercial operator specialising in mapping and area inspection, I’ve become known as someone who is adept in that area of the industry, indeed I get other operators asking me to do mission planning for them.

I originally started looking into it deeply as sometimes I only have just enough batteries to complete the job and one aborted flight can make the difference between getting the job done or not, properly programmed the software will do it more efficiently than flying manually and of course if you need to repeat the mission exactly multiple times then it’s ideal but as I said, I do a *lot* of them. I’ve learned to take into consideration all possible sources of risk, I scout the locations personally, closely examine the satellite imagery of the area and run simulations before hand. I have on occasion put 30 hours planning into a 20 minute waypoint mission where there was a zero margin for error. I don’t send a drone on a waypoint mission unless I am 100% sure it can complete that mission safely in case of a disconnection and were it to fall from the sky while disconnected that the likelihood of damage or injury is minimised as far as possible.

I just wanted to get that out there first.

So yes, the reason I disable them is because of possible behaviour in event of a disconnection. As you have said, “smart” return to home isn’t particularly smart. It simply measures battery drain over time vs distance travelled and when it thinks there is not enough battery to complete the flight it will come home. It is unable to take into account battery drain climbing as opposed to descending or flying out into a head wind as opposed to flying home with a tail wind. As long as you have carefully calculated the duration of the flight vs battery duration with a minimum 20% battery redundancy and you are not flying in particularly adverse wind conditions it’s more hindrance than help.

Obstacle avoidance on most DJI drones is known to be prone to false alarm especially when flying over water and or with the sun low in the sky. If you are disconnected from the drone through some unforseen circumstance and the obstacle avoidance false triggers you can be in a situation where the drone halts, attemtps to climb over a non existent obstacle, moves forward and then false triggers and halts again and attempts to climb, wash lather repeat.

This is not an theoretical situation. I have had this happen to me, managed to reconnect to the drone which had 12% battery by that time (over water) and managed to perform an emergency landing 700m from my location on the shore. The logs later showed it had falsely detected obstacles 16 times.

so yes, in a nutshell. If you are convinced of your ability to plan a safe waypoint mission and judge appropriate conditions to fly it under and you feel there is any chance of disconnection … turn off smart return to home and obstacle avoidance.

hope that helps

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