FPV enters forced landing mode unnecessarily?

[Pendolino]

Hi,

Playing around in the Malvern Hills today with the FPV, encountered a strange/unexpected behaviour.

Had a standard thrash about at treetop height (all in 'M' mode) down to 50% battery, then did a full power climb up to about 400 metres above take-off point, which obviously put the battery into a state of high discharge rate during the climb. This triggered a 'return to home immediately' prompt, shortly followed by it entering forced landing mode with the battery still at ~ 40%! Obviously it's still controllable and I brought it back safely, but I wasn't very impressed.

In 'M' mode, you can nose down and 'glide' back from that height using about 3-5% battery which was the intention.

Instead, it put it into 'N' mode and descended at the usual 5 m/s, which ironically used a LOT more battery than had I done it in 'M'.

Is this normal behaviour? When I saw the prompt to land, I did react by initiating the idle power/glide procedure, which would have resulted in a very low discharge rate, but it didn't seem to react to this and pushed on with the forced landing regardless.

I understand the reasons behind the forced landing in 'N' and 'S' mode where the trajectories are very predictable to the onboard computer, but it doesn't seem very compatible with 'M' mode, and it seems to base this on the 'average' power use over the last 'x' amount of time rather than using the true power output right now.

Flight was entirely legal and no, I haven't read the manual cover to cover!

Any ideas?

 

[slup]

Well... the critical low voltage auto landing is usually initiated when one cell goes below 3.0V (where it gets permanent damaged), and as the DJI FPV is a mix between a "photo drone" & a manual FPV quad they have decided to stick with the usual "photo drone" safety features, of which one is critical low voltage auto landing. The forced safety features doesn't become just recommendations when in manual mode so you can chose if & how you will obey it... they are forced & then it will land as they have programed it.

And the critical low voltage auto landing in it self is a clear sign that your type of flying is killing the battery... it's internal resistance is now so high that the cells voltage drops massively during amp draw, pushing the voltage below 3.0V where the internal resistance will increase even more.

Everyone that flies something where the cell voltage is directly shown in the goggles see this voltage sag directly... & let off from the throttle to save the battery, but DJI only shows a BMS calculated percentage that doesn't reveal this.

 

[Yorkshire_Pud]

Just for curiosity's sake how do you get permission to climb to 400m AGL ?
Are you going to post the flight log so that the battery voltages can be seen ?

 

[teccer]

Flight was entirely legal and no, I haven't read the manual cover to cover!

I hope you meant to say 400ft not meters

 

[Pendolino]

Well... the critical low voltage auto landing is usually initiated when one cell goes below 3.0V (where it gets permanent damaged), and as the DJI FPV is a mix between a "photo drone" & a manual FPV quad they have decided to stick with the usual "photo drone" safety features, of which one is critical low voltage auto landing. The forced safety features doesn't become just recommendations when in manual mode so you can chose if & how you will obey it... they are forced & then it will land as they have programed it.

And the critical low voltage auto landing in it self is a clear sign that your type of flying is killing the battery... it's internal resistance is now so high that the cells voltage drops massively during amp draw, pushing the voltage below 3.0V where the internal resistance will increase even more.

Everyone that flies something where the cell voltage is directly shown in the goggles see this voltage sag directly... & let off from the throttle to save the battery, but DJI only shows a BMS calculated percentage that doesn't reveal this.

Excellent info, thanks! If I see any preliminary warning regarding the battery or returning to home, I'll just give the motors a rest straight away then. A substantial amount of the (limited) FPV flying I've been doing has been 70-80 degrees nose down and full power.

Also, yes 400 metres, not feet. I think it was actually about 350-360. It was a big hill!

 

[Yorkshire_Pud]

400 metres, not feet. I think it was actually about 350-360. It was a big hill!

Ahh then might I suggest you edit post number one to read

"then did a full power climb up a hill to about 400 metres relative to the take-off point".

That assumes my 2nd interpretation is correct.

 

[slup]

If I see any preliminary warning regarding the battery or returning to home, I'll just give the motors a rest straight away then.

If you regularly end up with various battery related warnings directly related to amp draw you should really reevaluate the way you fly... or else you either will spend a lot on new batteries, or suddenly stand there without a drone due to a complete battery cell failure making the drone fall as a rock.

But yeah... always obey battery messages or warnings, don't just keep on with what you're doing, this piece of hardware is crucial to keep your drone airborne.

A substantial amount of the (limited) FPV flying I've been doing has been 70-80 degrees nose down and full power.

That's race quad behaviour... & racers kill their batteries during one or two heats, think you should try something that put your manoeuvring skills on test instead, you will find more thrill doing that & there you don't need more than 30 degrees & not even half the speed. Go low, near & through instead... much more skills needed for that instead of just bashing around on height in a straight line, everybody can do that.

I can easily damage or even destroy a brand new 6S 1300mAh LiPo on my 5" by just nailing the throttle on max for 30sec... will reach over 180km/h but then the fun is over & I need to do the "walk of shame", pick up the pieces & go shopping.

 

[Cafguy]

I can easily damage or even destroy a brand new 6S 1300mAh LiPo on my 5" by just nailing the throttle on max for 30sec... will reach over 180km/h but then the fun is over & I need to do the "walk of shame", pick up the pieces & go shopping.

this describes my shameful early days of flying quads! OH the Poor Batteries...