Mavic mini a 'scarey' loss of signal RTH

[Deleted member 103366]

Yesterday was a nice day, sunny, warm and thankfully very little wind. I decided to take the mini for some exercise.
The first flight involved a flight up a hill/ cliff and a peek over the top, I lfted maximum altitude to allow for the cliff's height (the flight ceiling rules are AGL here ). From a previous flight, last year, with a Phantom the cliff's top is around 110m above the take off point. I didn't take notice of what ceiling I set as I had no intention of going high over the cliff top, I just slid the button well up its scale. It turns out I must have set it to in excess of 875ft.
I do not like higher than necessary RTH heights so it set to 15m, the hill and cliff had no obstacles that the drone would have to avoid during an RTH.

The first flight was event free and after a bit of buzzing about around the take off point I landed and changed the battery for an out to sea flight.

I normally have the distance limit set to around 200m but I wanted to give the mini some room so I increased it.

I was just about at the edge of visual range i.e. max intended distance, when I got a signal loss which was quite sudden, there was maybe a second of pixelation and then boom, the connection was gone. (reasonably frequent glances at the screen)
At signal loss I was not worried, the battery was in the low 70%s, the drone was set to RTH at signal loss, and as far as I was aware the RTH height was 15m. The latter that turns out to have been VERY wrong.
A little later I see the telemetry start to change i.e. I had the telemetry connection back, though the video seemed frozen, BUT its climbing, !!!!!!!!! It shouldn't be climbing, it had been above 15m to keep it in sight. I thought to myself "it's got to be a trick or something of a weak signal" but it keeps on climbing, I lost sight of it. The connection was intermittant .
200ft "uuummm" ( I had switched to imperial units ), 300ft "UUUMMMM". Past 400ft connection seems to have stabilised but its still going up and I could not make it move towards home, the edges on panic showing themselves. I remembered at least one thread here? where the poster's drone climbed to a ludicrous height during RTH and was possibly lost. 500ft .....'wtf', Into the menus ...."oh mama" RTH height set to 875ft.

The problem with that is, not only does it use a lot of energy to get up there ( the battery was down to 61 or 62% as it stopped climbing ) it also takes one heck of a lot of time to come down, plus, what where the winds up there???? (As it turned out they must have been very light as the drone had no problem making good headway once it started moving forward). I tried to reduce the RTH height setting to stop the climb but every time I released the slider it sprang back to the 875ft setting. With hindsight I was trying to set thenew RTH height fairly low, below its existing height, maybe I should have tried an RTH height slightly above its at-that-time height.

With the Mini 'at the edge' of the communication range I did not want to cancel the RTH just in case that really threw a spanner in the works so it ended climbing to it's 875ft and then, thank goodness, started to move towards home. As soon as it started moving towards home I pulled the left stick down to start its descent.

When I was satisfied it was well within communication range I cancelled the RTH, moved the right stick forward and pulled the left stick all the way back for max descent rate whilst moving forward. It was back over head at a sensible height at about 30% battery.

There is absolutely not a snowball's chance in hell that I, deliberately, set the RTH height to 875ft. The only thing I can think of is that I must have accidentally touched and dragged the RTH height button whilst changing the distance limit. If that is what happened it's one heck of a bad coincidence with the 'extreme' maximium altitude setting because the App will not let you set an RTH height that is greater then the flight's ceiling and if you reduce the flight ceiling to below the RTH height the RTH height gets dragged down with the flight ceiling.

Lessons learn't
1) If changing limits CHECK you haven't made any accidental changes to something else.
2) Do not leave unnecessarily large height and probably distance limits in place from one flight to the next.
3) Ask if I should have cancelled the RTH before it got to 875ft?

I wanted to try a loss of signal RTH ( by switching the controller of etc ). but this was a bit beyond the pale

 

[BokiFly]

Maybe another lesson is that it's not bad idea to check RTH height before every take off, I do that most of the time, but probably not every time (sometimes I forget to check).

 

[Deleted member 103366]

Point taken and agreed with and I may have done that but, as I recollect, I changed the distance limit whilst the Mini was in flight so it might not have helped in this instance.

 

[scro]

Sounds a bit scary! The benefits and hazards of automatic systems! I sympathise with you, as changing these kinds of settings while keeping an eye on a drone in flight isn't as easy as you'd think, and easy to make a mistake.

It's just given me a thought that DJI will probably never incorporate into the app: A pre-flight checklist built in to the app. Something like a pop box with tick boxes/sliders that appears before allowing you to take off. It could contain all the usual things like check weather/wind, physical state of drone, battery level, max distance/height limits, RTH action, RTH height, gimbal cover off, etc...

Even better if it was customisable so you can add in the things that are important to you.

 

[Deleted member 103366]

A good idea.
What I really would like is having to type in numerical changes to limits, as you do in the Go and Go4 apps.
If nothing else I find these slider button adjusters in the fly app an absolute curse for accuracy

 

[scro]

Trying to move a slider on a small screen outdoors while flying isn't ideal. I too would prefer numerical input, at least as an option.

 

[Meta4]

I do not like higher than necessary RTH heights so it set to 15m, the hill and cliff had no obstacles that the drone would have to avoid during an RTH.

When you are climbing so high, it hardly matters what RTH height you set because the on loss of signal, if the drone is already above the RTH height it will just come home without climbing any further.

I tried to reduce the RTH height setting to stop the climb but every time I released the slider it sprang back to the 875ft setting.

Instead of messing around with the RTH height setting you should have just used the left joystick to descend and fly at whatever height you wanted.
p14 from the manual:

During RTH, the aircraft’s speed, altitude, and the orientation can be controlled using the remote controller or DJI Fly if the remote controller signal is normal, but the direction of flight cannot be controlled​

With the Mini 'at the edge' of the communication range I did not want to cancel the RTH just in case that really threw a spanner in the works so it ended climbing to it's 875ft ...

When I was satisfied it was well within communication range I cancelled the RTH, moved the right stick forward and pulled the left stick all the way back for max descent rate whilst moving forward. It was back over head at a sensible height at about 30% battery.

If you had control signal, cancelling the RTH would not have "thrown a spanner in the works".
Cancelling RTH and resuming control is a normal flight operation.

Lessons learnt
3) Ask if I should have cancelled the RTH before it got to 875ft?

You probably know the answer now.

Here's another useful pointer from p14 in the manual

In Smart RTH and Low Battery RTH, the aircraft automatically ascends to the RTH altitude. If the aircraft is at an altitude of 65 ft (20 m) or higher and has not yet reached the RTH altitude, the throttle stick can be moved to stop the aircraft from ascending. The aircraft will fly directly to the Home Point at its current altitude ​

I wanted to try a loss of signal RTH ( by switching the controller of etc ). but this was a bit beyond the pale

All flyers should experiment with RTH in a controlled situation, including cancelling RTH to resume control and switching off the controller to simulate loss of signal.
It's much better to understand how it works and what you can do than to be left wondering on the day you need to know.

 

[Dave Maine]

Note that loosing the video feed does not mean that you have lost control of the drone necessarily. You may still have ok joystick control. This ends up being pretty confusing, and prone to making expensive mistakes.

Stop doing anything with the controller, and figure out what is actually going on. If it is really a control signal loss, the drone waits 3 seconds and starts home. As it gets closer, you will eventually get the video download to start again automatically, and you can cancel RTH and fly as you wish.

If you still have control, you can bring the drone back using the radar display, or initiate a manual return to home with the controller button. My choice almost always is to fly it back manually so I get to choose the height, generally lower to avoid head winds.

If you were flying out into the wind, higher would be better, since the wind will help bring the drone back, conserving battery power.

 

[Deleted member 103366]

Many thanks Meta, many beep words later it looks like I am going to have to go through the manual........AGAIN.
Thanks David.

 

[timinator]

Because there are no obstacle avoidance sensors on the Mini, I had to get into the habit of changing the RTH height for every flight. With my Phantom 4 I took a set it and forget it attitude. For safety I just use 30m, 60m and 90m depending on where I am flying. First time I flew the mini and tried out RTH and it climbed to 90m which was what I initially set. It was a little windy and that's when I knew I had to treat it differently than the Phantom from an RTH perspective.

Slightly off topic but I marvel at some of the guys that say it handles great in wind in Sport mode. Well that may be true, but if you lose connection for any reason and it decided to RTH, man, you're just blowing in the wind at that point and about to join the flyaway club.

 

[Deleted member 103366]

Does anyone know of a way to deliberately block the control signals without switching the controller off?
If I want to experiment with control signal loss in a safe place I need to be able to block the connection. Putting the controller in stainless steel saucepans or tin boxes doesn't do it and if I switch the controller off it takes too long to reboot and regain connection with the drone by which that time the drone is likely to be overhead.
I recollect that with a Phantom 3 and GL300* it took the controller single digit seconds to regain control after switching it on

 

[OldEd]

Does anyone know of a way to deliberately block the control signals without switching the controller off?
If I want to experiment with control signal loss in a safe place I need to be able to block the connection. Putting the controller in stainless steel saucepans or tin boxes doesn't do it and if I switch the controller off it takes too long to reboot and regain connection with the drone by which that time the drone is likely to be overhead.
I recollect that with a Phantom 3 and GL300* it took the controller single digit seconds to regain control after switching it on

Maybe wrap the antennas in aluminium foil?

 

[scro]

.... Putting the controller in stainless steel saucepans or tin boxes doesn't do it a.....

Don't know if it'll help, but maybe try earthing the pan/tin box?

 

[Deleted member 103366]

Don't know if it'll help, but maybe try earthing the pan/tin box?

No I haven't......but I certainly will.

I will give aluminium foil wraps, earthed and un earthed a try too

 

[Motorcycle Rider]

Does anyone know of a way to deliberately block the control signals without switching the controller off?
If I want to experiment with control signal loss in a safe place I need to be able to block the connection. Putting the controller in stainless steel saucepans or tin boxes doesn't do it and if I switch the controller off it takes too long to reboot and regain connection with the drone by which that time the drone is likely to be overhead.
I recollect that with a Phantom 3 and GL300* it took the controller single digit seconds to regain control after switching it on

Put tinfoil on the antennas.
I did that to simulate loss of signal, but not have it too far away.

 

[EyesWideShut]

I wonder if putting tinfoil around the antennas may overload the receiver's electronics because of the transmitter's full power being reflected back inside the aluminum. Sorta like metal in a microwave burning out the magnetron. Doesn't the mini require about 10 seconds of LOS before RTH/Hover/Land starts? I wouldn't want to chance it to have the foil on that long plus any additional time to do your test.

Maybe walk close in behind a wall/building to block the signal and peak around it to keep VLOS.

 

[Zbip57]

Does anyone know of a way to deliberately block the control signals without switching the controller off? [...] if I switch the controller off it takes too long to reboot and regain connection with the drone by which that time the drone is likely to be overhead.

It takes between 10 to 15 seconds to regain connection after the Mini's controller is turned on again.

I did a series of four videos experimenting to see what happens when the control signal is lost on the way down if trying to do a forced landing in a remote location. It was only about 30-50m away from me at the time. I set my RTH height to 50m. Loss of signal was forced by switching the controller off. It takes a sufficient time for the Mini to climb to 50m, fly the 30-50m to overhead the Home position, and descend to land from 50m height, that there is plenty enough time available to regain the signal after switching the controller back on. There's even enough time in just the descent to landing from 50m height to easily regain signal on the way down.

Here's the YouTube playlist of those tests:

Mavic Mini - Forced Landing Tests

To force an emergency landing at a remote location...

www.youtube.com

 

[Deleted member 103366]

Thanks. Going through those videos now but as I am deaf I am having to try and read the subtitle or transcript at the same time. With regards to the forced landing thing during which you encounter loss of signal, are you aware that you can change the action on loss of signal to hover or land?

 

[Zbip57]

as I am deaf I am having to try and read the subtitle or transcript at the same time.

Ah man, I'm sorry about that. The automatically generated subtitles are often wildly inaccurate.

A long time ago I posted a bunch of videos explaining different features of my DJI Phantom-1 and I received a comment from Mitch Bergsma (of GoPro fame) asking if could add subtitles. He had recently bought a Phantom for himself, but since he's deaf he couldn't hear anything I was saying in the videos.

It's something that had never occurred to me before. I researched how to add closed-caption subtitles and re-edited a bunch of my previous videos to include transcripts. It's not a simple process trying to synchronize the script with the video.

Most of my videos since then have been silent, just music, or with titles written right onto the video screen. It's only once I started using a screen-recorder on my phone with the Mini to capture all the DJI Fly screen info that I began recording my own voice again to explain what's going on. Thanks for reminding me that not everyone can hear that. I'll do better from now on.

With regards to the forced landing thing during which you encounter loss of signal, are you aware that you can change the action on loss of signal to hover or land?

Thanks for that too. That was actually the whole point of that 4-video sequence.

The first three videos were done way back in December. There was so much talk about Minis being carried away in strong winds and unable to Return-to-Home because of the wind. Waiting until the Mini is carried out of radio range is fatal, because it'll stay airborne until a low battery eventually forces it to autoland. My theory was it would be better to emergency ditch-land the thing as soon as possible while you still have control. But that got me thinking, what happens if you lose control signal while trying to land it?

My previous DJI Phantoms gave the option of changing the Loss-of-Signal response, from RTH to Hover or Land. But originally there was no such option with the Mini. A loss of control signal always and only resulted in a Return-to-Home response. It would automatically start to climb back up to RTH altitude, where the strong wind would then carry it further away again.

I made those first three videos demonstrating this happening in various scenarios and sent the videos off to DJI. The result was v1.0.8 of the Fly app added the option to change between RTH, Hover, or Descend.

The fourth video in that playlist was done April 28th to test the new options of v1.0.8. If the loss-of-signal response is set to Descend, the Mini will now successfully continue to descend and land. Yippee! That is, unless of course "landing protection" kicks in when the Mini doesn't like the look of the landing area...

 

[Deleted member 103366]

with regards to " Ah man, I'm sorry about that. The automatically generated subtitles are often wildly inaccurate. " no worries, you couldn't have known and there's no harm done, it just takes longer to get through them.
And, oh yes, the automated subtitle are comical at times, compounded by an almost complete lack of punctuation. A mate texts like that and it takes me ages to decipher his messages

Thanks for that too. That was actually the whole point of that 4-video sequence.

ROFLMAO, I have put my foot in it again lol

Re " I made those first three videos demonstrating this happening in various scenarios and sent the videos off to DJI. The result was v1.0.8 of the Fly app added the option to change between RTH, Hover, or Descend".
WOW, WELL DONE, I thought they simply filed such things in the Buy It Now folder.