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[WARNING!] Autoland with half full/empty battery!

Discussion in 'General Discussion' started by Big Ben, Feb 24, 2014.

  1. Big Ben

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    Just experienced this which might be something to be aware of and keep in mind.

    Although it was still fairly windy it was also fairly sunny and I wanted to see whether I could shoot some nice images from a higher level than I had done before and at the same time test whether it would still be within the FPV WiFi range of my FC40.

    Previously I had increased the geofence ceiling in steps going from 30m to 50, 75 and 100m and had flown at those altitudes. I now had it set to 150m. During my first flight I noticed when I had gone to perhaps 50m that the Phantom was drifting downwind without stick input. I had to give forward stick to move against the wind. Apparently the autonomous manoeuvring speed wasn't high enough to compensate for the wind drift. I decided not to push it and descended again. It would seem that the wind gradient was stronger than I had experienced before.

    Next battery I tested again at moderate height and this time it held position so I went higher up. I shortly tested drift in ATTI and also moved a bit upwind for extra margin and generally flew with more (prolonged) full forward stick than I probably had done before. Suddenly I noticed it was descending. I hadn't initiated that. Then I noticed a red flashing light so I concluded it was in L2 autoland mode. I was very surprised since I use a timer app that warns me every minute and also signals the 6 and 7 minute mark above which I keep it gradually closer. Between the 7 and 8 min. mark I usually begin to see red flashes. I couldn't imagine I would have somehow missed the signals and quickly checked the timer to see that it wasn't even close to the 6 min warning. I actively descended my Phantom and checked at low hover for a short period whether the red flashes would disappear again but they didn't so I quickly landed. Total flight time was about 5:50. Flight time after L2 autoland must at least have been 30 sec. That battery has given me flight times of around 8:30 with FC40 camera attached. After disconnect I checked the voltage and it was 11.4. Usually it is at 11.2-11.3 at home and shortly after the flight probably lower but since I don't push the limits I don't routinely check the voltage in the field.

    I reconnected the battery and got green flashes. I decided to fly it again to see how much extra flight time I would get until L1 and the usual landing time. I flew another 3:10. Clearly the battery wasn't really empty the first flight.

    My guess is that the fairly aggressive full forward stick use due to the strong wind caused the voltage to drop below the L2 autoland level. Fortunately it was perhaps only 15 m away from me horizontally but something like this might cause greater problems when flying further out and/or at lower altitude if you are caught by surprise still expecting several more minutes of uncomplicated flying time. I could see the red flashing pretty soon but at greater distance this won't be recognised as easily.

    I am not at all sure the Phantom switches back from L2 autoland to L1 if the voltage rises again. Something I'd like to know. DJI should know this but I haven't read any info about this.

    I'm now wondering whether I should set my L2 voltage a notch lower. I don't know how much less margin that would give me in real L2 autoland situations before the Phantom would drop uncontrollably.

    This wasn't the original battery but a Hacker 2400 Topfuel. Have others experienced L2 autoland kicking in prematurely as a result of aggressive stick use?

    And does anyone know whether the Phantom can/will revert to L1 warning level and will abort autoland when voltage rises again?
     
  2. ElGuano

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    It's normal behavior. Aggressive flight = more current drain = voltage sag = low voltage alarm. A low C discharge rating can trigger it earlier as well.

    I don't know if the autoland cancels if your voltage pops back up, I'd imagine it doesn't because you would have unreliable throttle input.

    Sounds like you're doing things the right way. As long as your after flight voltages are nominal and you're not hitting 3.3v/cell loaded your batteries are being treated well.
     
  3. OI Photography

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    That would be my guess too, esp with the heavy drain overall and especially the spikes that happen in windy conditions. I've definitely had the voltage drop to nearly the auto-land point but then bounce back and let me fly for 2 more minutes, but never quite went over the threshold...usually when I know I'm getting close to the last couple of minutes of time left I try to not fly too aggressively (or in heavy wind) to avoid exactly what you ran in to. I have no idea if you can kill autoland while it's in process, but I do know that if it gets on to the ground you won't be able to lift off again even if you have enough juice left in the batt, unless you power the Phantom off and then back on again (I had that happen once or twice a while ago).

    What are your voltages set at? On my Phantom 1.2 with maddog 2700 batt I have my 1st-level final voltage set at 10.7 and the 2nd-level final voltage (i.e. auto-land trigger) at 10.6. You might want to go quite that low, or to keep that tight of a difference between 1st and 2nd level (to give you more warning time), but you might be able to drop a bit lower than you have now. It'll just depend on your specific batt and flying conditions.
     
  4. FangsCPO

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    Think of aggressive flying like flooring your gas pedal and add a low c battery, i.e. a stock battery which is rated at 20c, you will trigger your 1st and 2nd safety spots almost immediately. I started using Dronefly Lipo 2250 45C, those lipos had great punch and I could get about 6.5 minutes with a CM2000 v2 Gimbal and HERO3 attached on my Phantom v1.
     
  5. Big Ben

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    My voltages are still at their defaults 10,7/10,6. Setting L2 at 10,5 will avoid this effect to some degree but will reduce the safety margins. Since I don't want to make it a habit to fly in such windy conditions I'll probably leave the voltages as they are. I did it this time because I felt my Phantom had enough windy flight hours to have proven itself as being sufficiently capable of handling these conditions but not being able to auto-hold position due to the wind to me kind of signals that you're starting to push the flight envelope. Occasionally OK if you know what you're doing and know what boundaries not to cross but not something you should habitually engage in.
     
  6. Bigbells

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    Over 12 minutes with stock battery in windy conditions

    Since you were able to land manually, doesn't that mean that you had to have been in L1 landing mode rather than L2? I thought that L2 was completely automatic and that it took all control from your hands, but I could be wrong.

    I figured I'd test my battery life today. My FC40 has the stock Phantom 2200mah battery and is otherwise stock except that I use the 9" DJI Phantom Vision rotors in place of the stock 8" rotors. [Side note: although I'm pretty sure I get longer battery life and higher full-stick speeds with the bigger rotors, I like the way the 8" stock rotors fly. I also find that the stock rotors are tougher and less likely to chip if the quad tips over on take-off or landing or collision with sneaky trees. They're definitely less costly to replace.]

    Constant wind today is upward of 11mph. I don't have an anemometer, the Bing weather report for this immediate vicinity said 10mph when I left to go outside, 11mph when I got back inside, and 16mph now, just 15 minutes later. My best guesses as to wind speed during my flight: 12mph with gusts to 18mph. (That really is just a guess, based on nothing but inexperienced intuition regarding wind speeds, but it is nevertheless my best guess.)

    Anyway, I did little except hover during the flight. The quad had to fight very hard against the wind. It was really getting battered around. In the second half of the flight I brought it down from approximately 30 feet to approximately 12 feet, in order to get a little protection from the wind.

    I got 12 minutes 10 seconds of flight without going into L2 automatic landing. When I ended the flight by catching the quad in my hand it was spending more time flashing red than flashing green. I didn't dare land on the ground because I didn't feel like damaging half a quad's worth of rotors, which is $20. Quite a few times the flashing green would change to flashing red but would change back to flashing green. As soon as I got back inside, I connected to the NAZA M software and observed a battery voltage of 11.13 volts. My Level 1 low battery alert is set at 10.7 volts. I don't remember whether I set it there or if that is instead the default setting.

    At any rate, I think I could have flown fairly aggressively in calmer conditions and still gotten more flight time. I mention this test simply because it seems I'm getting better than average time out of a battery charge.

    If you want to judge for yourself how strong the wind was, or to verify that I did fly for over 12 minutes, the otherwise boring video from the FC40 camera is here:
    http://www.youtube.com/watch?v=EJqU27j5 ... e=youtu.be
     
  7. ElGuano

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    L2 doesn't take away control from you, it just increases the throttle required for hover progressively until it's 90%. It is essentially making you land, but you otherwise still have full control.

    10.7 loaded alarm recovering to 11.1-11.2 is pretty normal.
     
  8. Big Ben

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    That sounds like it behaves the same as when doing RTH. I was wondering whether Autoland might be similar to RTH too in the respect that you can take control back by switching to ATTI mode.

    Maybe when in L2 Autoland due to aggressive flying it might be possible to revert to L1 or even normal flight when flying with less power drain by flicking to ATTI too (or perhaps even to Manual).

    Has anyone ever tried this? If not it might be worth trying next time you experience a premature L2 Autolanding.
     
  9. jthorstad

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    What timer app do you use? I'd especially like something that will alarm at set marks, like 6, 7 minutes...
     
  10. Big Ben

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    I use this one. It could use some extra features but I find the timer very useful. It beeps every minute counting down, three times a minute before the set time and six times at the set time which for me with the FC40 camera is 7 minutes. Then I've set it to count up.

    It also provides a basic log with running total flight time. I run it on my Nexus 7 while for the FC40 camera/FPV I use my phone. Once I've found a practical solution to mount my N7 to the Tx I'll switch them.
     
  11. OI Photography

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    Good point, I'll give it a shot the next time I fly (hopefully later today) and let you know.