When Your Drone will Return to Home (RTH) and When it Might Not…

[rscheff]

It appears that there are many ways that drones perform the RTH. It varies within different types of the same manufacturer and also different between manufactures. I have a cheap $100 drone that claims when RTH is initiated the drone will follow "the same path" back to launching site. It did not.

As far as the DJI Mavic Mini 1, the book says it will automatically initiate RTH on several occasions. One: If contact to the drone lasts more than 11 seconds it will RTH. Two: If the battery drops below 20% it initiates RTH in ten seconds unless overridden by pilot. Three: If battery drops to 10% it will again initiate RTH, but it can be overridden again. I have overridden RTH right in front of me, less than 3 feet off the ground, until battery was below 0% and not until then will it automatically land with me having no control. BUT, I have also had my drone make an emergency landing right where it was, when there was 92% battery. I had some control but very little, I could not stop the decent but I could navigate, which avoided the drone crashing into outside restaurant diners. I sent the flight record to DJI and without any acknowledgement from them there was an upgrade issued which addressed RTH problems.

There seems to be 3 different "Loss of contact" situations where RTH is supposed to activate. One is when you fly the drone out of range of the RC. In my case the distance of "Loss of contact" varies from day to day. One day it will be 900 feet and another day it could be 1,800 feet. Experimenting with this in my area is scary, very congested and many trees, I could easily lose the drone. But I did do it twice, once by accident and the other on purpose with 2 people involved to keep drone in sight. Both incidents the drone did not RTH and could not be initiated manually. I had to physically move closer to the drone to regain contact. I again sent the flight records to DJI and they told me to return the drone.

I am on my 4th or 5th drone, have lost count. Not all were because of RTH problems, two were gimbal problems.

I Now have another new drone (had it for 3 weeks) and I discovered 2 more "Loss of contact" situations. They are both initiated by me and both should have same results, RTH, but do not. One: I unplug the remote controller from the phone. Two, I shut off the remote controller. Bot cause "Loss of contact" and the same error message, but unplugging the RC does not initiate RTH. WHY?

I guess the moral of the story is: Don't trust anything that drone companies are telling you, it is still a very new technology and by making them more available to the average person they have to cut corners in manufacturing. There seems to be a lot of bugs (just reading the posts) in the RTH, but I guess that is one reason they tell you not to fly out of sight. But still, with all the issues, they are a lot of fun to fly. Just have to realize that drones are in no way perfect and realize they may not perform the way advertised.

 

[Zbip57]

I unplugged the RC from the phone by physically unplugging.

It is the remote controller that controls the drone. Unplugging the phone will not trigger RTH. You still have control of the drone, even without the phone, and even without the DJI app running.

The controller communicates directly with the drone. Telemetry and video signal is sent back from the drone to the controller. That info is shared to the phone and Fly app via the cable connecting the controller to the phone. If you disconnect that cable, or shut down the phone, it just means you won't get to see any of the video signal and the app cannot record any of the telemetry. But you still have full control of the drone via the joysticks on the controller. Therefor RTH is not automatically triggered if the connection to the phone is removed. You can still trigger RTH though by pressing the button on the controller.

It is possible that only the video signal can fail, leaving you without a video display on your phone, but you might still have a good control signal.

If the control signal is interrupted or lost for more than 11 seconds, the Mini will automatically engage it's Failsafe protocol of RTH, Descend, or Hover, depending on which default setting you've selected.

I have my RTH set to RTH.

Just a point of clarification. You have your "Control Signal Lost" setting configured to RTH.

Return to Home is always RTH, unless it's triggered within 20m of the recorded Home Position in which case it'll land right where it's currently at.

I tried unplugging and turning off. [...] every time I unplugged the RC, RTH was not initiated automatically. Every time I shut off the RC RTH was initiated automatically. In both cases the error msg. was the same, "AC disconnected from RC".

Unplugging the phone from the controller does not interrupt the control signal from the controller to the drone. So RTH will not be initiated automatically.

Turning off the controller does kill the control signal, therefore the configured Failsafe response of RTH will be automatically triggered 11 seconds later on the Mini.

In both cases, unplugging the phone or turning off the controller, the DJI Fly app running on your phone can no longer receive any telemetry info from the drone. The app is disconnected from the drone so the log file on your phone ceases recording any info.

In the cases where there was NO RTH I physically plugged the RC back in.

When you unplugged the phone from the controller, have you tried to see whether the controller still controls the drone even without the phone attached? It should still work.

I've never actually tried that myself. I'm just charging up a battery right now and will try.

If I just left the RC unplugged until battery down to 19 % I don't know what will happen, have to try that next.

Normally the system knows how far away from the Home Position the drone is currently at, and it knows how much battery is needed to get back home. (But it is notoriously inaccurate in compensating for any strong headwinds that might be encountered on the way home.)

Once that low RTH battery level is reached, you'll get a notice that the drone is about to automatically go home, with a countdown timer giving you enough time to abort the procedure if you prefer. If you do nothing, the drone will automatically go home.

I assume that's all calculated and handled by the app itself. If you have the RC unplugged and the app disconnected at the time, I'm guessing none of that will work.

There is a second "critical" battery level warning, that I'm sure is handled by the drone itself and has nothing to do with app. Once that critical low battery level is reached, the drone will commence autolanding where it's at right now. You can still steer it on the way down, and you can temporarily slow or even prevent its descent by adding throttle input. But eventually the battery can only do so much...

 

[Zbip57]

I Now have another new drone (had it for 3 weeks) and I discovered 2 more "Loss of contact" situations. They are both initiated by me and both should have same results, RTH, but do not. One: I unplug the remote controller from the phone. Two, I shut off the remote controller. Both cause "Loss of contact" and the same error message, but unplugging the RC does not initiate RTH. WHY?

Both cause loss of contact with the phone and app, but unplugging the phone does not cause loss of contact between the controller and drone. Unplugging the USB cable between the controller and app will not trigger RTH, because you still have full control of the drone.

When you unplugged the phone from the controller, have you tried to see whether the controller still controls the drone even without the phone attached? It should still work.
I've never actually tried that myself. I'm just charging up a battery right now and will try.

Okay, I tried it.

As expected, unplugging the USB cable between the controller and phone only interrupts the data signal to the app. But it does not affect the controller's signal connection to the drone. You still have full control. Here's the video:

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[LoudThunder]

Okay, I tried it.

OK, you may have tried it but you did not try much, you made a point at 0:25 on your video to show the viewer the Home Point and then you fly outside the No-RTH distance (less than 20-meters) and fire off the RTH, but you never let the drone actually RTH, you cancelled the RTH each time… Oh the drone acted like it would, but would it actually find Home and would it actually Land… When I started this Topic, I made my Mini 2 work for its "money…" Inquiring Minds Want to Know…

 

[rscheff]

I understand now what you are saying. If the RC is on but not connected to the phone the drone and RC can still communicate. And yes I did try flying with the RC unplugged from phone and yes I did have full control. When I shut off the RC I had no control and RTH was activated. But I still had 2 horrible experiences where the RTC did not function as it was supposed. The drone went into emergency landing with 92% battery and I had no control over the descent but I did have some navigation control, enough to get the drone back to a safe landing. Then twice I flew out of range, once by accident and then once on purpose. Both cases RTH was not activated within 11 seconds. I could only get control of the drone by driving towards it and regaining contact. Below is a copy of the recorded flight log of the automatic landing. The squiggly lines are my attempt to steer the drone back to me all the while the drone keeps descending. I was luck the drone was not far away and there were no trees. There were a lot of theories thrown around, like, flying in an airport zone. But, I fly in this same zone everyday and I had already made several flights before this happened. I never went back to that area. There seem to be a lot of quirks with the RTH in all drones, and all drone companies. It may also be an issue that I fly a lot and may have a better chance of something happening to me. DJI sent me an award a couple months ago saying that I flew the Mini, in 2021, more than 97% of all mini pilots around the world. My wife says that only makes me a bigger nerd with too much time on my hands. Whatever I like flying.

 

[Zbip57]

OK, you may have tried it but you did not try much, [...] you never let the drone actually RTH, you cancelled the RTH each time…

Sorry, but that really wasn't the point of the video. @rscheff seemed to believe that unplugging the USB cable between the controller and phone should cause the drone to automatically RTH, which it does not do. I merely demonstrated that one still has full control as long as the controller's signal to the drone remains uninterrupted. There's no reason for it to automatically go into RTH mode when the USB cable is unplugged.

I know for a fact that, once RTH actually is triggered, the drone will return to home exactly as advertised. There was no need to wait for a full landing in this particular video.

If you're interested in seeing a full RTH exercise, then check out my playlist of four videos below. When I first bought my Mini in December 2019, there originally was no other Loss of Control Signal Failsafe option other than Return-to-Home. That got me thinking of doing some experiments.

At the time, there was many reports and YouTube videos of people losing their brand new Minis while trying to fly them in too strong winds. If you panic and watch your Mini being carried away by the wind, eventually it will drift far enough away that you lose the control signal. At that point it should automatically trigger RTH. However, if your RTH height is configured to some higher altitude that only makes the situation worse if the winds are even stronger at that greater height. The Mini already can't fight it's way back against a strong headwind, so the even stronger headwind at higher RTH altitude only makes things worse, and it's gone. Bye-bye.

So what should you do differently to save your Mini in such a case? My thoughts were you should try to land it immediately at any convenient remote emergency ditching location, while you still have control of the drone within range of the control signal. But what happens if it loses signal on the way down, behind a hill, or tall building, or dense forest? That's what I wanted to test in this series of videos.

The first three videos demonstrate conclusively that, in such an emergency, the Mini's automatic response of RTH would prevent any attempt to ditch the drone at a remote location if the control signal was lost on the way down. There was no way to FORCE it to land if the control signal was interrupted during descent, because then it would always automatically go into RTH mode.

I sent those three videos to DJI Support asking why there was no other option in the Fly app. The DJI Go app for my previous Phantoms provided the options of RTH, Land, or Hover in the event of loss of signal. But the Fly app for the Mini included no other options, only RTH.

Four months later DJI issued a revised version of the Fly app which now included those same three options in the event of Loss of Control Signal -- RTH, Descend, or Hover,. The fourth video in this playlist demonstrates how this can be useful. If you select "Descend" as the Loss of Signal failsafe response, the drone will continue to land at your chosen ditching site, even if the signal is lost on the way down. [Caution: Do NOT leave it configured like that if you, like I, do most of your flying over lakes and forests!]

This playlist runs all four videos in sequence:

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[LoudThunder]

You brought up a Great Point about forcing a landing in the event you cannot get your Drone home due to high winds and there is the possibility you might lose visual. I never thought about using the Landing Option in the App to force a landing. The next time I'm out with my Mini 2, I will practice this. I'm a firm believer in testing procedures to know, feel, and experience an event before it becomes an emergency. Which is why I practiced the RTH in the original posting.

Kudles on your "Forced Landing - Test 1"

 

[mickmmm]

It appears that there are many ways that drones perform the RTH. It varies within different types of the same manufacturer and also different between manufactures. I have a cheap $100 drone that claims when RTH is initiated the drone will follow "the same path" back to launching site. It did not.

As far as the DJI Mavic Mini 1, the book says it will automatically initiate RTH on several occasions. One: If contact to the drone lasts more than 11 seconds it will RTH. Two: If the battery drops below 20% it initiates RTH in ten seconds unless overridden by pilot. Three: If battery drops to 10% it will again initiate RTH, but it can be overridden again. I have overridden RTH right in front of me, less than 3 feet off the ground, until battery was below 0% and not until then will it automatically land with me having no control. BUT, I have also had my drone make an emergency landing right where it was, when there was 92% battery. I had some control but very little, I could not stop the decent but I could navigate, which avoided the drone crashing into outside restaurant diners. I sent the flight record to DJI and without any acknowledgement from them there was an upgrade issued which addressed RTH problems.

There seems to be 3 different "Loss of contact" situations where RTH is supposed to activate. One is when you fly the drone out of range of the RC. In my case the distance of "Loss of contact" varies from day to day. One day it will be 900 feet and another day it could be 1,800 feet. Experimenting with this in my area is scary, very congested and many trees, I could easily lose the drone. But I did do it twice, once by accident and the other on purpose with 2 people involved to keep drone in sight. Both incidents the drone did not RTH and could not be initiated manually. I had to physically move closer to the drone to regain contact. I again sent the flight records to DJI and they told me to return the drone.

I am on my 4th or 5th drone, have lost count. Not all were because of RTH problems, two were gimbal problems.

I Now have another new drone (had it for 3 weeks) and I discovered 2 more "Loss of contact" situations. They are both initiated by me and both should have same results, RTH, but do not. One: I unplug the remote controller from the phone. Two, I shut off the remote controller. Bot cause "Loss of contact" and the same error message, but unplugging the RC does not initiate RTH. WHY?

I guess the moral of the story is: Don't trust anything that drone companies are telling you, it is still a very new technology and by making them more available to the average person they have to cut corners in manufacturing. There seems to be a lot of bugs (just reading the posts) in the RTH, but I guess that is one reason they tell you not to fly out of sight. But still, with all the issues, they are a lot of fun to fly. Just have to realize that drones are in no way perfect and realize they may not perform the way advertised.

I'm only a beginner and on my second drone. The first was a type of E58 selling from AU $70 up to may be $150, so very cheap and still fun but with tones of unpredictability and only 5 to 7 minutes flight time.
The second, my present SJRC F11 is way better, 5 times bigger but still a cheap toy. And I guess this is where it's all meaningful.
If I make the comparison with mobile phones and their development ....You get what you pay for. And aeronautic is a very different technology with different concerns. Smart phones progress is phenomenal probably because of the money they generate whereas drones have not the same status!
So for casual users it's a little dilemma. Going for the top prices, meaning several thousands dollars or going budget price.
The risk of loosing them may not be exactly the same, yet it is a big gamble to invest in an expensive drone that probably would be so much more reliable but perhaps just as easy to damage or loose; especially for the non professionals and less gifted pilots.
So all we can do in the lower end is wait for improvement within the same cost. Yet forum /fora may help to share experiences and get solution to some problems
This is right, don't fly your drone out of sight (this includes against the sun, or a dark background like trees etc., in restricted space areas, or in a bad weather. To mention a few.
My wish is to have a switch or a way to disable the auto rth on low battery. I would not mind either to find a way to fix my my camera (or rather un-fix it!) as it will respond to the adjustment only for a few seconds after starting it, then get stuck looking up. So now I got it taped to a horizontal angle (180) Which is not ideal but works!