High wind and RTH

[BokiFly]

Few days ago I had a warning "Strong wind warning. Aircraft unable to return to home automatically. Lower altitude immediately and return to home manually ", first time ever that I had that warning, and few seconds later I lost connection with the drone because in that moment Mini was around that distance in town area where lost connection could happen. So Mini was at the distance where it can lose contact with me (not always but it can), and in the same time I had a wind warning and after that I lost contact with him. In that moment I was wondering what is the real meaning of that "Aircraft unable to return to home automatically" part. Does that mean that RTH will not even be activated? Because in that situation only RTH can bring Mini to me (like in many other situations when RTH worked great). I did what I can, I just waited to see will connection be established during RTH, because I was hoping that RTH will be activated. And it did. Like in many other situations in some moment I got video and saw that Mini is returning, like always.

I don't know how DJI programmed behaviour in this situations, but I think that RTH should alway be activated if we lose contact with the drone, no matter how high wind is.
I don't know does that works in that way, or DJI disabled RTH during high wind, and I just got lucky that maybe wind decreased in strength so that RTH could be activated.

What do you thing?

I hope it is the first scenario.

Only thing that we can do better manually than automatic RTH is that we can lower altitude (avoid strong wind), where RTH will first go up where wind is even stronger. But when it comes to flying in line I can't do anything better than automatic system. They can set RTH to automatically switch to S mode if there is a strong wind. I don't know does it work in that way, but it should, it's logical. Only problem is the altitude, because RTH altitude must be achieved (and we often play safe and set it even higher than it should be).

So I hope that message "Strong wind warning. Aircraft unable to return to home automatically. Lower altitude immediately and return to home manually " doesn't mean that RTH will not be activated, but it only suggests that we should lower altitude and return manually. If we don't lose connection in the same time

This could be tested if someone will got high wind warning and just press RTH button, and observe what will happened. I hope that RTH will work. In addition I would programmed it that in that specific situations (wind + no connection + RTH) drone go to S mode, because we can't do that manually if we don't have connection.

 

[sar104]

The message simply means that the aircraft's wind speed estimate is, at least transiently, higher than the aircraft's maximum speed in normal mode (which is what RTH uses), and that it may not be able to make it back to the home point in that mode. It doesn't change the failsafe behavior and so if failsafe (lost connection) is set to RTH then it will still try to RTH.

 

[old man mavic]

@BokiFly ,the warning was just that ,it was saying that in the event of a RTH ,then because of the amount of battery remaining ,verses the distance it would have to travel against the wind to return home ,at the RTH height that was set ,then it would fall short of its objective
so to prevent such a scenario it was advising you to reduce height and fly home manually if you had done this then by seeing how much headway you were making against the wind ,you could have then chosen whether to go into sport mode or land somewhere where you could retrieve the drone

 

[sar104]

@BokiFly ,the warning was just that ,it was saying that in the event of a RTH ,then because of the amount of battery remaining ,verses the distance it would have to travel against the wind to return home ,at the RTH height that was set ,then it would fall short of its objective
so to prevent such a scenario it was advising you to reduce height and fly home manually if you had done this then by seeing how much headway you were making against the wind ,you could have then chosen whether to go into sport mode or land somewhere where you could retrieve the drone

It would be nice if the calculation were that deep, but that would just be implemented as an additional factor in calculating the SMART_BATTERY_goHomeBattery parameter - it wouldn't wait until it is too late to provide a warning. And so the fact that those warnings arise before the auto RTH kicks and since we don't see changes in SMART_BATTERY_goHomeBattery with height as wind speed increases suggests that the RTH function still doesn't include wind speed and direction and that the warning is just a wind-speed-triggered message.

 

[old man mavic]

It would be nice if the calculation were that deep, but that would just be implemented as an additional factor in calculating the SMART_BATTERY_goHomeBattery parameter - it wouldn't wait until it is too late to provide a warning. And so the fact that those warnings arise before the auto RTH kicks and since we don't see changes in SMART_BATTERY_goHomeBattery with height as wind speed increases suggests that the RTH function still doesn't include wind speed and direction and that the warning is just a wind-speed-triggered message.

thanks @sar104 ,i am not quite as eloquent as your good self in putting down in words what i am getting at, but i do understand what you mean about the drone not really knowing what the actual wind speed is at where it is flying

 

[QuestionTime]

I got this message almost every flight when flying here in the UK, so I never really used the RTH unless the wind speed was between 0 -5 mph.

Be mindful with the Mini in terms of how light it is vs wind/gust speed and your altitude - the higher you fly, the stronger the wind.

 

[BokiFly]

The message simply means that the aircraft's wind speed estimate is, at least transiently, higher than the aircraft's maximum speed in normal mode

How does it calculate that?
By looking at motors RPM, moving drone speed comparing to estimated speed on current motors RPM?
Airdata had that part "Wind Map" but only in paid version, as I understood they use some algorithm to calculate wind speed and direction from LOG file. Probably DJI uses similar method to calculate wind speed and to send warnings.

I don't have paid version on Airdata yet, but if someone does, how accurate looks their "Wind Map"?

 

[sar104]

How does it calculate that?
By looking at motors RPM, moving drone speed comparing to estimated speed on current motors RPM?
Airdata had that part "Wind Map" but only in paid version, as I understood they use some algorithm to calculate wind speed and direction from LOG file. Probably DJI uses similar method to calculate wind speed and to send warnings.

I don't have paid version on Airdata yet, but if someone does, how accurate looks their "Wind Map"?

It uses the known relationship between tilt and airspeed in steady, level flight, combined ground speed from GNSS velocity.

 

[BadWolf1]

There is an entry in the logs "FailSafeAction" which seems to usually be "GoHome", and is sometimes "Hover" in the ones I just checked - I think I have also seen "Land". I'm not clear what causes it to switch out of "GoHome" (possibly when failsafe is already causing it to go home), and if that fails it will stop and hover. Then if it can't hover it will land.

From what @sar104 said, and @old man mavic 's comments I think the message is saying slightly more than the system is doing - in effect "You might not get home if you go up into stronger winds with automatic RTH". I think the warning is simply a matter of wind speed - I think (@sar104 , you seemed to suggest this too) it will display the message even if the wind is helping you to get home.

 

[Deleted member 103366]

"......They can set RTH to automatically switch to S mode if there is a strong wind. I don't know does it work in that way, but it should, it's logical. ......"

unfortunately from the bottom of page 11 of the manual

" If the aircraft is further than 20 m from the Home Point when the RTH procedure begins, it ascends to the preset RTH altitude and flies to the Home Point at a speed of 8 m/s "

which is basically the max speed in P mode.

I am not sure if that 8m/s is airspeed or ground speed BUT I have seen the indicated speed (which I assume that is ground speed) increase if I push the 'forward-stick' forward so .....if it can not beat the head wind in automated RTH I'd suggest as well as descending try moving the forward-stick forward and holding it there. Infact providing it is pointing in the correct direction I'd suggest considering cancelling the rth and switching to S mode.
I do not know how fast you can make it go in RTH because when I have thought to check I have never had the flight distance to allow it to accelerate to maximum speed, I tend to do a lot of flights less than 100m long. When I have done a 'long' distance RTH I have never thought to take notice of the maximum speed reached

 

[sar104]

There is an entry in the logs "FailSafeAction" which seems to usually be "GoHome", and is sometimes "Hover" in the ones I just checked - I think I have also seen "Land". I'm not clear what causes it to switch out of "GoHome" (possibly when failsafe is already causing it to go home), and if that fails it will stop and hover. Then if it can't hover it will land.

From what @sar104 said, and @old man mavic 's comments I think the message is saying slightly more than the system is doing - in effect "You might not get home if you go up into stronger winds with automatic RTH". I think the warning is simply a matter of wind speed - I think (@sar104 , you seemed to suggest this too) it will display the message even if the wind is helping you to get home.

You can change the failsafe setting between RTH, Hover and Land in the DJI GO 4 and Fly apps:


DJI GO 4


DJI FLY

That setting is displayed in the MC_PARAM_failSafeAction txt log field but, for some reason, is not necessarily correct until failsafe occurs.

 

[sar104]

"......They can set RTH to automatically switch to S mode if there is a strong wind. I don't know does it work in that way, but it should, it's logical. ......"

unfortunately from th bottom of page 11 of the manual

" If the aircraft is further than 20 m from the Home Point when the RTH procedure begins, it ascends to the preset RTH altitude and flies to the Home Point at a speed of 8 m/s "

which is basically the max speed in P mode.

I am not sure if that 8m/s is airspeed or ground speed BUT I have seen the indicated speed (which I assume that is ground speed) increase if I push the 'forward-stick' forward so .....if it can not beat the head wind in automated RTH I'd suggest as well as descending try moving the forward-stick forward and holding it there. Infact providing it is pointing in the correct direction I'd suggest considering cancelling the rth and switching to S mode.
I do not know how fast you can make it go in RTH because when I have thought to check I have never had the flight distance to allow it to accelerate to maximum speed. I tend to do a lot of flights less than 100m long and when I have done a 'long' distance RTH I have never thought to take notice of the maximum speed reached

8 m/s is the target ground speed. The airspeed could be higher provided that it doesn't exceed the maximum P- or N-mode tilt. It will not increase to the S-mode tilt maximum; that's an arbitrary decision by DJI but may be because OA won't work properly at those higher tilt angles.

 

[Deleted member 103366]

Sorry sar104 but, during an RTH, I have frequently seen the indicated speed increase when I 'push it', if my 'pushing' has, by chance, coincided with a lull etc. in the winds it is a very frequent coincidence. I am not arguing with you, these are merely my observations.

 

[BokiFly]

if it can not beat the head wind in automated RTH I'd suggest as well as descending try moving the forward-stick forward and holding it there

So we can control something during RTH and it will not fall off from RTH? That is great. We can lower altitude DURING RTH, so no need to cancel RTH just to lower altitude because of that strong wind? We can let RTH direct drone to home point and we can change altitude? I suppose we can't do roll or yaw during RTH.
But adding speed, if it's already going 8 m/s (max in P mode) can we go faster than that just by pushing the stick? That will in some way push it into S mode.

I didn't understand what is the difference between "ground speed" and "airspeed".

 

[Deleted member 103366]

You have control during some of the RTH's notably the manually triggered "Smart" one, (the only sort I have encountered so far with the mini) but I can not guarantee that you have full control during all of them. You need to read the manual to check that and try them out under safe conditions.
I do have a recollection of reading the description of one RTH where your control in minimal but I can not remember which DJI drone that related to, sorry
I recollect that I have yawed and rolled during an RTH but bear in mind my flights are predominantly within my 100m or so long and narrow garden so any deviations from the original RTH course are minimal. Again, if you wish to try experiments with the RTH do them in a safe area, it's what I WILL be doing once I start getting out and about again.

 

[sar104]

Sorry sar104 but, during an RTH, I have frequently seen the indicated speed increase when I 'push it', if my 'pushing' has, by chance, coincided with a lull etc. in the winds it is a very frequent coincidence. I am not arguing with you, these are merely my observations.

If it coincided with a decrease in wind speed then you might see all kinds of transient changes but, since the maximum ground speed in P- or N-mode is 8 m/s, it will not consistently exceed that.

 

[scro]

Ground speed is how fast the drone is travelling compared to the ground. If you are flying the drone back to you it is how fast the drone is coming towards you.

Air speed is how fast the drone is moving compared to the air around it. If there's no wind this is the same as ground speed. If you're flying full speed into the wind and getting nowhere your airspeed is high (ie 13m/s) but your ground speed is 0m/s

 

[Motorcycle Rider]

I still retain control of my mini during RTH.
I can speed it up, slow it down, yaw, climb, etc.

 

[EyesWideShut]

I still retain control of my mini during RTH.
I can speed it up, slow it down, yaw, climb, etc.

As @Motorcycle Rider and @PhiliusFoggg point out during RTH you can speed up, slow down, climb, descend and yaw. The only thing you cannot do is change course. It's Returning To Home in a straight line but you can adjust the other parameters. Great if you need extra speed because of the wind or a lower altitude to get out of it if it's safe to do so or want to yaw your camera around while returning for a different view.

 

[sar104]

As @Motorcycle Rider and @PhiliusFoggg point out during RTH you can speed up, slow down, climb, descend and yaw. The only thing you cannot do is change course. It's Returning To Home in a straight line but you can adjust the other parameters. Great if you need extra speed because of the wind or a lower altitude to get out of it if it's safe to do so or want to yaw your camera around while returning for a different view.

It doesn't give you extra speed against the wind because in RTH the FC will already use the maximum tilt allowed in normal mode. To fight any harder against the wind will require cancelling RTH and switching to sport mode.