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P2 Low voltage landing behaviour - what's normal?

Discussion in 'Phantom 2 Discussion' started by MrJoshua, Nov 17, 2014.

  1. MrJoshua

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    I had an 'incident' yesterday which thankfully only cost me a prop, and a little time carefully bending my zenmuse arm straight again but it could have been much worse. I want to get to the bottom of why it happened, but at the moment the info seems unclear. Hopefully I can blame it on pilot error, ensure I don't repeat in future, and therefore trust the phantom again.

    I'd been flying my P2 LOS very close for about 10 minutes at most, with gimbal and gopro, and a TK102 tracker (about 40g) attached.
    Behaved perfectly and I tested out the failsafe return home by switching off the TX, and it worked perfectly.

    Flew it again and it was getting a bit breezy so I moved downhill slightly to a sheltered spot.
    That's when there was a problem.

    After maybe a minute in the air, the P2 switched into Evil mode (fast red flashing indicating low voltage, but the battery lights were still good), stopped responding, and started to climb rapidly.
    I couldn't get any input so I switched to manual and did a heavy landing that caused minor damage (a prop, and a ding on the gimbal).

    I have two specific questions about the behaviour of my P2 if anyone can clarify, as this will help put my mind at rest:

    1) Low voltage auto landing -
    When the low voltage auto landing sequence is invoked (NOT the failsafe return home ie lost signal etc), does the P2 climb to a fixed height first before landing, or does it just descend from wherever it is when the low voltage condition is met?

    All the videos I've seen on youtube appear to show that the phantom just descends from the height/position it's current at, and this makes sense to me because if you're at a critical voltage there may not be enough power remaining to climb first before landing, like the failsafe return home function does.

    I haven't seen any videos of the P2 or P1 where there is an ascent under the low voltage auto landing, but I really need to clarify if this should be the case or not? Ideally a link to something DJI have written that describes whether this happens or not, or videos demonstrating where it's very evident.



    2) GPS home lock (rapid green flashes) -
    I've seen it a few occasions now when running the startup sequence of my P2 that it will display the home lock rapid flashing, change to normal operation steady green flash, then some seconds later repeat the home lock rapid flashing a second time.

    It then continues with the normal steady green flash and works fine, but I haven't seen other people describe this second home lock behaviour so it makes me slightly nervous that it's not normal and could indicate a problem?


    The bottom line is that I think possibly I have a battery problem (I only have one pack so I can't compare), as it still appeared to have good power but also looked like a low voltage incident was triggered (ie the flashing red lights).

    Fair enough if that's the case (although I'd still be very upset if I have to pay for a new battery when it's not old at all), but why then did the bird start rapidly climbing at this point instead of landing? All the stuff I've found shows them just landing where they are in low voltage emergency, so it 'seems' more like a flyaway but maybe I'm wrong? Happy to admit to pilot error if that's the case but I want to be able to clearly show that's what happened to give myself reassurance that it wasn't bad behaviour from the P2.

    Here are some other details that will get asked I'm sure:
    *Compass calibrated immediately before flight.
    *Wifi disabled on gopro and phone.
    *TX and P2 on latest firmware.
    *Battery has only been used approx 11 times.
    *Home lock was definitely acquired before lift off.

    One other thing I wanted to ask is re' the compass calibration.

    A mate has told me that it's important to ensure the P2 is pointing North when you begin compass calibration. I haven't heard/read this until he said it, and non of the videos I've seen suggest this must be done so I'm not convinced, but he says it's important to ensure it works correctly and that it solved a problem he had with his gimbal drifting. Like I say, I'm a bit skeptical about this as it's not the most practical thing that you have to strictly know which way north is every time etc (I know it's not that difficult but still)...

    Thanks guys!
     
  2. phantomi

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    There are two things that call my attention. You switched to manual and because of the breezy condition you move to a sheltered area. Last one can cause a drop in satellites count and how do you switched to manual? Are you in NAZA or Phantom mode?
     
  3. MrJoshua

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    Thanks for the reply. I say sheltered but I just mean slightly to the side of a slight hill. In terms of satellites it wouldn't have made any difference tbh as the p2 was back at the height where it was clear of that hill anyway (ie it was a bit of a pointless move on my part but I continued as it wasn't proper windy, just the odd bit of breeze). Even at the side of that hill it'd have full clear sky as the hill was only about 4m high and a gradual slope, so once in the air it'd be a non issue and it locked on fine even on the ground.

    I have it set up in Naza mode as GPS/Atti/Manual.

    I'm happy enough about it being in manual mode at that time despite the more difficult control.
    No regret about that at all as I believe without that it may have fled without any means of stopping it. That's the whole reason I set manual up.

    But I'm just interested in finding out 1) for absolute fact what the low voltage landing behavior is, and 2) if the repeat home lock flashing is a problem or normal.
     
  4. phantomi

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    It appear you don't have FPV so although you have 3.08 firmware can't check battery history. I don't know if in the assistant you can check for battery problems. For what I have read there is no such NORTH thing while calibrating compass and if there is low battery it will definitely not ascend. With my limit knowledge there is nothing more I can tell. Good to know that if it was a fly away problem you can recover.
     
  5. MrJoshua

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    Thanks mate. Still waiting for tx so no FPV yet no. The bird was maybe 10m away from me so very clear etc.

    So no ascend on low voltage landing then for sure? If that's the case then surely that means it was indeed a flyaway, and presume no way to know why.
    Makes me really nervous about using again if it's happened once...
     
  6. 750r

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    1st set of flashes CL
    2nd set is 6 or more sats you want to see both before taking off .
    I have heard when calibrating compass start facing north I can say I've never done it and haven't had any problems it sure won't hurt if you do it .
     
  7. phantomi

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    Don't be afraid for this, it could be anything else. My only advice is to set S1 lower position to RTH and try it without turning off transmitter. I have never liked to turning off and on the transmitter with the quad up there.
     
  8. MrJoshua

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    750r- CL? Not sure what you mean sorry bud? It's the same rapid green flash that confirms home location locked, except that sometimes it happens twice.

    I don't want to set the s1 to RTH because I've read countless stories of flyaway a happening when RTH failed to work either by itself or on the switch, whereas manual (as risky as it is) seems to still give response, as happened for me.
     
  9. phantomi

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    I suggest it because your apparent fly away take place after the switch off on the transmitter. I remember once that my quad was landed and I was trying to drain a little more the battery, then while it was idling I switch off the Tx to see the quad behavior, few seconds later I switch on the Tx and altough the quad was below 12% battery it almost take off. I had to place my hand over it so it didnt take off. Also for what I have read most Phantom Pilots has the S1 bottom in RTH.
     
  10. RobertMfromLI

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    What happened was totally normal. At the 20% threshold on the new firmware (or next previous version), the copter will climb to a pre-defined height (check in the Phantom Assistant - mine was 67' - I changed it to 200'), then leisurely return home, then leisurely land.

    If there is NO GPS signal at the time, it will auto land exactly where it is. The same happens on critical battery level.

    In EITHER scenario, switch to ATTI mode (S1 switch (RIGHT switch) to mid or to closest to you position) and fly home, keeping in mind that the features available in GPS mode are no longer enabled.

    In the battery section, there seems (in the newest firmware) to be an option to disable RTH on low battery - but the copter will STILL auto-land on critical battery.
     
  11. MrJoshua

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    Thanks guys. Phantomi - I don't believe the event occurred because of the TX being turned off, because after it did RTH and landed safely I powered down the P2 and the Tx, then carried out a complete fresh startup cycle, with a full sat lock.

    RobertMfromLI - thanks, I might be confused but your first comment describes return to home failsafe rather than the low voltage auto landing, which are two different things. I cannot find anything on DJI's documentation or webpages that describes the low voltage landing being anything like return to home (ie using GPS to return after first climbing).

    This is taken from the DJI Wiki for the P2:
    There's no mention anywhere of an automated ascent/climb under low voltage condition, nor use of GPS to move to a predetermined position?

    It's feasible that they wiki is out of date compared to the firmware and doesn't reflect what actually happens now, so I'm not saying that your comments are wrong, but I just would really love to see the definite process laid out somewhere official if anyone can point me to a page that describes what you've said, or a link etc.

    Sorry if that sounds like I don't want to agree - I really appreciate the input but I just keep hearing conflicting info and want to find some formal point of confirming it so it's not in doubt, yet cannot find any such info. On that basis, I'm curious as to how anyone else can be certain rather than anecdotal evidence etc?

    Am determined to get to the bottom of this, and I appreciate the input and discussion. :)
     
  12. MrJoshua

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    Well I've emailed DJI to ask them to clarify whether the low voltage landing just descends where it is without any action more clever than that, or whether it does ascend to a set height then return home before landing.
    I'm not convinced they'd have it climb and try a clever return technique when it's at a very low battery level since it could cause way worse damage than setting down where it is, if it climbs then loses power or drops out of the sky en route to the home point.

    I might be completely wrong, and probably lots of people will wonder why I'm making a thing of it, but it's important that I find out as then I will know if mine was carrying out a normal process for low voltage (and therefore I sabotage it!!), or if it was suddenly going 'off piste' - in which case, how can I trust it in future?

    That's why I'm trying to get clarity on the question. Plus of course it might help someone else in future to know.
     
  13. RobertMfromLI

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    The newest firmware says otherwise - so does the Phantom Assistant software itself. What I posted above is from the firmware changelog, and the Phantom Assistant software.
     
  14. RobertMfromLI

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    Here's what I have found...

    All firmware from v3.06 upwards does what I wrote above (per both the firmware changelog notes and the Phantom 2 Assistant software):
    • 20% battery (in GPS mode with GPS signals): automatic return to home at the height you defined via the P2 Assistant (or default height if you haven't changed it)
    • 20% battery (with too few or no GPS locks): automatic "land in place" enabled
    • CRITICAL battery level (either 8% or 12% or 15%, but I can't remember what the firmware notes said): automatic "land in place" enabled
    • Regain control when either option above activated: switch to ATTI mode
    • Disable (theoretically) return to home on 20%: go to battery page of P2 Assistant (NEWEST version) and uncheck the RTH option. The "critical auto land" option is unable to be disabled in the newest firmware (except by bypassing it via ATTI mode).
    • S1 (right) switch changes modes between GPS (position 1, forward), ATTI (position 2) and ATTI (position 3).

    The notes above are from a combination of their firmware release notes, and the P2 Assistant and actual testing.
    http://download.dji-innovations.com/dow ... tes_en.pdf

    Those threshold changes are not in the firmware changelog for the relevant firmware levels of when they changed it to two warning levels.

    But consistently, exactly, and always at 20%, RTH activates on my copter, since 3.06. Prior to that, it never did. I am usually at about the same distance from the RTH point.

    AND HERE'S WHERE IT GETS INTERESTING:
    I read someplace that distance to return safely is factored in, meaning that battery level might vary before RTH is activated.

    Probably confuses things even more. Definitely looking forward to what they tell you.

    Best,
    Rob
     
  15. phantomi

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    I'm glad all we can understand better what can cause your quad behavior and that it is consonant with the firmware instructions. It gave me a knowledge reassurance while enjoying it.
     
  16. MrJoshua

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    Thanks Rob, that's really useful and it does explain a lot!

    So it sounds like Pilot error then in view of what you've posted, and I'm more than happy to accept that as it means I don't have to worry about bad behaviour of the P2 - makes me much happier!
    A little embarrassing to know that I sabotaged an otherwise healthy auto landing but it confused me as I had only just updated the firmware and I think prior to that it would have behaved in a more understandable way (from the perspective of just setting itself down like in all the videos I've seen).

    This all being the case, I can't wait to get back up there, although I'm still waiting for my FPV TX, new props, longer landing gear, and a polariser for my gopro.

    I'm still a little hazy on why it does a second apparent home location lock though sometimes, but my main concern appears to be solved, so thankyou. :)
     
  17. OBX Kevin

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    I had a very similar thing happen to me. I'm still configured for "Phantom" mode versus Naza. I saw a couple of led red flashes so I proceeded to maneuver it back to me to land. Just as I was about to sit it down the thing took off straight up and I saw the fast led red flashes. It didn't appear to be responding to to me so I moved the S1 to the middle and then back up. I then had regained control and brought it down quickly. I'm guessing that it was in the process of ascending to the return to home height due to low batteries. It freaked me out because it wasn't allowing me to control before I toggled the S1. When a Phantom 2 enters the "return to home" state, is it normal to lose control over it? I'm not sure what it would have done it I didn't do the toggle and gain control. All I know is it freaked me out as I'm a newbie and I've read too many stories of fly aways. I always do my due diligence prior to lifting off.
     
  18. TeamYankee

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    It's normal to "lose" control when the RTH failsafe is activated, either due to low battery or interference.
    Flipping to ATTI mode and back will recover control.

    As mentioned previously the actions on RTH activation can be configured to "land in place" or fly to the "home point" (wherever that may currently be) and land.
    The P2 (non vision) does not have a range limitation with regards to the battery state and the location of the home point, so on a "low battery" alert it will start RTH regardless of distance to the home point and it could easily run out of power on the way home and start the auto land sequence in the middle of nowhere.

    Prior planning of the flight will prevent this, take into account the ambient air temp, now that winter is upon us, when estimating the flight times as it affects the battery discharge rate.

    It's more scary when going full "tilt" in ATTI mode and the low battery RTH is activated... the quad skids to a stop in mid flight and ascends to the RTH altitude with a total lack of user control. Just remember to go to GPS then back to ATTI mode to recover, or leave it fly home.

    I've also noticed the double green flashes when awaiting the GPS lock... This explains it...

    Once the Naza has a decent GPS signal (usually after 10-20 seconds) you will see a multiple row of green flashes:
    G G G G G G G G G G G G G G G G G G G.
    This signals that the Naza has recorded it's "Home Position" (for failsafe and RTH).
    If you want one word of advise: don't ever fly your quad until you see this long row of green flashes as your failsafe WILL NOT WORK unless it has recorded the home position.

    Then, only if you have IOC enabled, then you will get another set of green flashes about 5 seconds after the first set:
    G G G G G G G G G G G G G G G G G G G

    This is to tell you the Naza has recorded it's "Forward Position", in other words it's recorded which way it's facing via the compass. The Naza only needs to record this information if you have enabled IOC in the Naza assistant software and use "Home Lock" or "Course Lock" modes. If you do not use or have not enabled IOC via the Naza assistant software then you WILL NOT GET THIS SECOND LOT OF GREEN FLASHES, EVER.
     
  19. MrJoshua

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    Ahhh, that explains it perfectly - I do have IOC enabled. Brilliant, thankyou TeamYankee (and RobertMfromLI)

    This thread has been REALLY useful and put my mind at rest. Good work gentlemen.
     
  20. MrJoshua

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    New prop came today so I can get right back up there again. :)