Venture
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Sean-bumble-bee Posted at 7-29 02:28
"by flying at 21 mph for some 30 seconds AFTER AutoLand was triggered "
With respect to the mini 2, the above comment appears to demonstrate that you misunderstand the control that the pilot has during the various phases of low battery response.
Phase 1) Low battery RTH, which you cancelled " with RTH cancelled at 25%" (from the Mavicpilots thread )" and is not part of the subject matter of this thread.
1. Amazingly good explanation of the 4 phases of Autoland. Thank you Sean-bumble-bee.
When DJI chimes in with a few missing trigger numeric details, DJI should use your explanation in their manual.
2. Thank you for suggesting PMing a Moderator to get my answers.
I believe Tony has voluntarily taken up that baton, thank you both.
3. I've recently learned wind was at most a small factor for this flight.
Unusual battery burn was due to me flying back at full speed in Sport mode
(I flew it uphill in Normal mode) which reduced distance able to fly, from 20-25% according to the logs.
4. Mini2 was 100 feet above and 100 feet short of a grassy hill when signal was lost; it was 200 feet (not rounding those numbers off more than a foot, really) above the steep terrain, and 675 feet above Home.
5. I really appreciate you and Bashy and Yorkshire_pud's 's helpful civil, respectful comments and willingness to learn from each other. Reminds me (favorably) of early computer user group days.
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SBB Observation 1:
"by flying at 21 mph for some 30 seconds AFTER AutoLand was triggered "
With respect to the mini 2, the above comment appears to demonstrate that you misunderstand the control that the pilot has during the various phases of low battery response.
Response 1: I use throttle, steering and up-elevator often during my occasional low and critical low-battery landings, and have reviewed numerous reports and youtubes about its various phases to know its use well enough to hand-land at zero percent after a six-mile flight.
But there are some DJI programming Priority overrides and trigger levels I do not yet understand - that apparently only DJI Firmware programmers can clear up.
What I might not have made clear is that the 21mph was almost certainly due to my using full-throttle in Sport mode (just seconds earlier at 25-30mph) and keeping full-throttle on full-time after Autoland triggered until signal loss. That automatic mode switch from Sport to Autoland reduced its speed to ~21 mph.
SBB Observation 2:
Phase 2) This is a 'forced' descent phase.
Like "low battery RTH" this starts at variable battery percentages. UNLIKE low battery RTH "phase 2" is INDEPENDENT of distance from the home point, it depends SOLELY on the drone's barometer-deduced height and is intended to get the drone on the ground before the battery becomes exhausted and, from memory, with battery charge to spare. It is also completely independent of AGL since, in this respect, the drone knows nothing of its AGL.
Response : Ok, so it turns out to be vital to know what that variable battery percentage number is.
DJI Are you listening?
PS did you really mean this 'forced' descent phase 2 is triggered purely by the Barometer?
SBB Observation 3: I think you misunderstand this phase, you have FULL control during the initial stages of this phase and are able to fly the drone horizontally at up to full speed. You can in fact force a climb. I recollect, during the landing phase of a low battery RTH, with the drone near the ground and, as an experiment, forcing the drone to climb, fly over my house and then, via releasing the sticks, land on the other side of the house. This explains why you were able to fly at 21mph during the intial part of "phase 2".
Response : Actually I was not only aware of control here, I was using it here, at full throttle and turning, trying to get it to a nearby grassy meadow. Wasn't sure it was full control, as it was going slower (21 mph instead of Sport mode's 25-30+).
SBB: However, as the battery charge gets lower and closer to the "phase 3", it is likely that you will be given warnings that amount to "there is not enough power left in the battery to reach or sustain the commanded speeds" and the achievable speed will be reduced. These reduced speed-limits apply to the drone's ability to fight wind as well. From memory these behaviours have been documented in several lost-drone flight logs on here and or mavicpilots.
Response : I'll try to find some of those posts. Thanks.
SBB: Inability to fight wind may be a factor in your flight's descent.
Response : As noted above, the max "gusts" it was enduring were only about 7mph. Pretty minor compared to losing 20-25% of distance because I was trying to fly too fast using Sport mode.
SBB: Phase 3) The critical battery phase.
The threshold for this is fixed, I do not remember what that threshold is but when within this phase the notable feature is greatly reduced horizontal speeds which diminish as the battery drains. Again this affects the drone's ability to fight wind.
Response : So knowing the Firmware critical battery phase threshold is rather vital.
DJI - Why isn't it published in the manual?
SBB: In addition the drone can reject the landing site. This means that, without pilot input, it will hover until the battery is 'exhausted'. If this happened to your drone and the drone's flight path was unobstructed by shrubbery & terrain it could have been blown downwind. I tested "rejected landing site" behaviour during my early ownership of a Mini 2.
Response : Love to learn what you discovered in your testing of Landing Site rejection.
Did it ever make sideways moves or turns, or back up? What kinds of places does it reject - soft, brushy, rocky, steep?
SBB: Phase 4) 0% and below.
I have read of people keeping their drone in the air 'below' 0% battery and possibly saving their drone whilst doing that, by getting the drone over a safe landing place, but it is a while since I read any such thread or perhaps watched a suitable youtube and I do not remember the drones concerned. However it is my recollection that, at 0%, a mini 2 will descend irrespective of the amount of throttle and that it will ignore elevator and alieron inputs. At the heights I have performed such experiments I would have very little time to judge whether there was even minimal horizontal control and, given that my landing sites are often in confined spaces, I would have no inclination to try horizontal movements.
Response : I've read a few amazing reports as well.
One fellow claimed he flew 2,000 feet (600m) After his batteries reached Zero !
If I'd known about that and tested it previously - I might have had better fortune trying to fly all the way back home, rather than landing early in a grassy hill top - that turned out to be blocked from controller signal.
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SBB I understand your questioning if automated behaviours would start during "Phase 2" and in fact automated behaviours can and do start after disconnection, yes I know that that is not "phase 2".
I can confirm that a low battery RTH will start after disconnection if the failsafe behaviour is set to hover and connection is not re-established BUT I suspect that, since you cancelled the intial low battery RTH, a second low battery RTH will not be initated after disconnection unless, perhaps, your 21mph etc. managed to get the drone 'ahead' of the trigger threshold for the then distance.
Whether or not Failsafe RTH, if set, will be activated during "phase 2" I do not know.
But even if the failsafe RTH does start, it is first going to burn off 11 seconds of battery power in the delay period and then more battery in the "retrace". Yorkshire_pud's "shimmies" of post#8 open the possibility that the "retrace" may three dimensional, if it is in 3D then not only would the drone be, at a guess, flying away from the home point but it will also be climbing. Both aspects would drain the battery still further and bring the drone closer to speed restrictions and "phase 3".
A: So Failsafe RTH cannot trigger for 11 seconds after signal loss?
That's useful and helpful.
I'm back to my original question - wondering if,
since it was already deep in AutoLand mode at 11% battery,
will Failsafe RTH trigger at all due to the critically low battery?
or does AutoLand keep Total Control?
SBB: Aside from movements stemming from any automated behaviours that may or may not have started, there is your comment "Battery draining abnormally fast" on the mavicpilots thread. That comment suggests that the drone was fighting a head wind and a significant head wind at that. With respect to position, any such wind may have become a significant factor during the descent of your drone. We can not even guess this because, since you will not post the log, we can not work out how far the drone had to descend. Nor can the wind the drone was encountering be estimated.
Response : As an international, multi-decade hang-glider pilot & instructor, who knows those specific hills from years of soaring and hiking, its possible I an estimate those low-level winds fairly well.
A: I've recently learned wind was not the significant factor for this flight. Wind was nil at takeoff (teaching hang gliding for years has me extra sensitive to slightest breezes) and only "gusting" up to maybe 7 mph in flight.
Unusual battery burn was overwhelmingly due to me flying back at full speed in Sport mode which reduced distance able to fly, from 20-25% according to the logs.
SBB: If you seek information from DJI i.e. the "horse's mouth" then I suggest you PM one of the mods, point them at this thread and ask them to pass your questions "up the chain".
Response : Good idea, & Done.
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