Was this a low-battery autoland? (vid inside)

[Prime12]

Earlier today I was descending straight down to land at the end of the flight (about 18 minutes in, Zenmuse H3-2D with Fatshark FPV). I usually try to avoid coming straight down to avoid VRS but today I was flying over a neighborhood (my dad had asked me if I could take a few pictures of his newly redone roof) so I didn't have a choice.

Anyways, while descending, the Phantom suddenly yawed and started dropping in a hurry. I thought I had gotten into VRS so I tried giving it some cyclic but it kept dropping. While I didn't have any control over the Phantom I still had camera control. Somehow it did slow itself down a bit at the end of the flight and come out unscathed.

But why?

I still had 30% battery at the point the Phantom started dropping. Since my first level warning was set at 20% I thought I had plenty of battery to land. Both the battery and the Phantom are fairly new, less than 5 flights old.

Ok, sorry about the rambling. So, does this look like a low battery autoland? Do you think it might have been something else?

[youtube]https://www.youtube.com/watch?v=OhYTZclxL00[/youtube]

 

[4wd]

Hard to say, doesn't look like VRS.
I wouldn't have expected it to say you still had 30% left after 18 minutes because that's a long flight with extra stuff underneath -
but in any case by 30% the voltage will start to dive.
Unless you really need to push it, it's wise to be quite conservative with these batteries and bring it home before 40%

 

[Hughie]

18 minutes is impressive to 30%. I cant get much more than 12 or 13 mins down to 20%.

 

[David2676]

what is VRS ...

 

[SteveMann]

No, it does not look like VRS because VRS would not yaw the aircraft. Since the gimbal would remove any of the antics of VRS the video doesn't show anything abnormal.

For David: VRS = Vortex Ring State. In rotorcraft as you descend air is compressed below the craft and much of that compressed air spills over the rotor plane in a vortex. Because the rotor plane is a circle, it's called ring vortex. The vortex pressure will decrease the lift from the rotor. So the unaware pilot adds cyclic to stop the descent (throttle in multirotor aircraft), which increases the downwash pressure which increases the vortex pressure which exacerbates the problem. Eventually you run out of cyclic or power and the aircraft comes straight down. In helicopter flight training you are taught to move laterally to get out of a VRS. The reason a multirotor wobbles when it's in VRS is because the lift from all the rotors is not compromised the same and as one rotor plane recovers another loses lift.

 

[jason]

Earlier today I was descending straight down to land at the end of the flight (about 18 minutes in, Zenmuse H3-2D with Fatshark FPV). I usually try to avoid coming straight down to avoid VRS but today I was flying over a neighborhood (my dad had asked me if I could take a few pictures of his newly redone roof) so I didn't have a choice.

Anyways, while descending, the Phantom suddenly yawed and started dropping in a hurry. I thought I had gotten into VRS so I tried giving it some cyclic but it kept dropping. While I didn't have any control over the Phantom I still had camera control. Somehow it did slow itself down a bit at the end of the flight and come out unscathed.

But why?

I still had 30% battery at the point the Phantom started dropping. Since my first level warning was set at 20% I thought I had plenty of battery to land. Both the battery and the Phantom are fairly new, less than 5 flights old.

Ok, sorry about the rambling. So, does this look like a low battery autoland? Do you think it might have been something else?

[youtube]https://www.youtube.com/watch?v=OhYTZclxL00[/youtube]

That is exactly low battery level go home feature and it works the same way as failsafe. My suggestion is to uncheck that feature in P2 assistant software or the next time you may be underneath something when that feature is triggered.

 

[Marlin009]

Were the lights flashing red?

 

[Hughie]

It can be surprising how quickly the battery level starts to decay once you approach 30%. I have just checked one of my recent IOSD-mini/FPV recordings and it takes just 1 minute 11s for my battery to go from 30% to 20%.

Are you sure you had 30% at the moment that autonymous decent started, or, do you mean that at some time shortly before it started to decend, you had 30% ?

 

[Prime12]

Good point. It was definitely shortly before the descent started. I just checked the battery I had used for this flight (funny I never bothered to check this until now) and it's at 17%.

...which means it went from 30% to 17% in less than a minute. I think I'm going to stop relying on my 'fuel gauge' from now on!

Also, I think I now know why the Phantom suddenly yawed. The red circle in the attached picture is my launch pad / home point. What probably happened was that as the battery approached the cut-off point it triggered the go-home function and the Phantom started heading for its 'home.' It's just that the forward movement was so subtle I hadn't caught it until now.

 

[Hughie]

Good point. It was definitely shortly before the descent started. I just checked the battery I had used for this flight (funny I never bothered to check this until now) and it's at 17%.

...which means it went from 30% to 17% in less than a minute. I think I'm going to stop relying on my 'fuel gauge' from now on!

Also, I think I now know why the Phantom suddenly yawed. The red circle in the attached picture is my launch pad / home point. What probably happened was that as the battery approached the cut-off point it triggered the go-home function and the Phantom started heading for its 'home.' It's just that the forward movement was so subtle I hadn't caught it until now.

OK then, I would put this down to nothing mysterious - just a low battery level trigger doing its job.

 

[Prime12]

Hughie, you were spot on. Today I charged up the same battery and hovered around while paying close attention to the battery gauge on my iosd.

Sure enough, once past 32% or so, the battery level started dropping alarmingly quick (and I was just hovering around!!). In fact, I immediately started landing at 25% (from 7-8 meters, took MAYBE 10 seconds), yet when I checked the battery level after I landed, it was down to 18%.

I think I'll be completely disregarding the 'fuel gauge' from now on!