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  1. Pedals2Paddles

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    This is somewhat common question and occurrence here. So I thought I would make a thread for people to reference on the topic. This describes how to recognize, avoid, and respond to botched landings. If anyone here flies full size aircraft, you'll recognize this is really no different than recognizing when it's time to go around.

    Landing Detection: To understand why this happens, you need to understand how it's thinking first. The solo detects it has landed in the same manner regardless of being in Fly, Fly Manual, or Automatic (RTH, RTM, etc). The pixhawk flight controller detects that it has landed when it's vertical speed is nearly zero (within +/- 20cm/s) for one second despite the motors being at minimum throttle. This takes place when it lands itself automatically, or when you land it manually using the sticks. If throttle is at minimum, either by way of the stick being down or the auto landing reducing power, and the solo stops descending, it is obviously on the ground and will shut down. Note that in these cases, you do not need to move the throttle stick to the left also. Just fully down will do it. Fully down and fully left really only applies to stabilize mode now.

    Refusal to disarm, copter won't stop: If it balloons back up, tries to takeoff again, or otherwise refuses to stop and disarm, there are a few common reasons. It's easy for new pilot to get flustered here. Don't.
    1. A rough, fast, rocky, or unpleasant approach and landing will throw off the accelarometers in the IMU. Therefore, it will not be able to detect that it has stopped. It will essentially be disoriented and think it's still in the air. Since it isn't suicidal, it will not disarm if it thinks it's still in the air.

    2. Air pressure from the prop wash feeding back to the barometer will make it think it is changing altitude. This is mostly suppressed while landing, but it will absolutely compound problem #1 above. It can also happen by itself if have a small narrow landing area that forces the prop wash back onto the solo.


    To recover from this situation: First of all, stop fighting it. You're making it worse. If you keep trying to manhandle the controls to force it down, it will just make things worse. if you try to grab it by hand, you'll make it way worse, and probably hurt yourself. Relax.

    1. Climb up to 5-10 feet and hover. Just give it 5-10 seconds at 5-10 feet so the flight controller can clear it's head. Then land gently as normal. In nearly all cases, it will work properly this time around. If for whatever reason it still refuses to disarm...

    2. Bring it down and hold it down using throttle fully down. Use your free hand if you have one to activate the A+B+Pause kill switch (hold all three buttons for 5 seconds). It will stop. Or another options is....

    3. Put Stabilize mode on the A or B button. Land manually in stabilize mode. Throttle stick fully down and fully left will disarm. If you're comfortable flying in stab, this is a great mode to keep on your A or B button along with Fly Manual. This is one of the reasons. But for a lot of new consumers used to fly and fly manual modes, you'll probably just crash. So it requires practice.

    Flips when landing: If you have a situation as described above, and the copter flipped over, this is likely why. Remember, it thinks it is still flying. The copter tries to adjust it's horizontal position or adjust it's pitch/roll attitude due to unlevel ground, GPS drift, or pilot stick inputs. There is 1 or more legs on the ground that drag and it will tip itself right over. This is why, as I said above, stop trying to fight it.

    The other cause of flipping while landing is hitting the ground while still moving horizontally, catching a leg, and over it goes. This can be due to you moving it around, also know as pilot error :). It could be due to gust of wind hitting it. Or it could be from GPS drift while in FLY or RTH modes. So again, land gently and slowly. Fighting and man handling any aircraft to the ground almost always ends badly.


    Crash Detection: The flight controller has a number conditions it uses to detect it has crashed, or to detected it is in flight but beyond recovery. This usually works fine. But, if you've tipped over and it doesn't automatically stop, use the A+B+Pause kill switch to stop the motors. What's happening here is just like everything else above. It thinks it is still in flight and is trying to recover itself. If the pitch/roll is still less than a certain point, as in it isn't completely flipped over, it will not comprehend that it has crashed. For example, if it is just nosed over resting on the props, it will think it is in flight and pitched forward. So it's trying to compensate for that.
     
    #1 Pedals2Paddles, Sep 9, 2016
    Last edited: Sep 9, 2016
  2. User Name

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    Great info. Only thing I would add is that under the latest firmware, A+B+Pause seems to cut the motors pretty much immediately. Previously, you had to hold them for, as you said, 5 seconds or so.

    If I was already on the ground and it wouldn't disarm, I'd probably go for the A+B+Pause - if the flight controller is confused, the last thing I want is to put it back in the air. It's not hard to reach over and hit those buttons with your right hand, especially if it's already firmly on the ground.

    Lastly, and somewhat related, be aware of GPS visibility at your landing site. The closer you are to the ground, the more likely there are to be obstructions and the more your position fix quality will degrade. If you're in a GPS assisted mode, this could lead to unexpected moves if the position fix is lost or on the verge of being so. In these cases, it's best to put it in Manual for the final approach and landing. Unless it's seriously windy, you'd probably be hard pressed to tell the difference between Manual and Fly, but this is another example of why it's good to be comfortable in Manual.
     
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  3. Toiletbowl

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  4. RichWest

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    This is how I do it....100% Fly mode, with stick full down until disarm.

    The good old days, when the video stopped when I told it to...

     
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  5. 1tom2go

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    Thanks for sharing this! I have had some little landing issues on a sloped spot. It powered up after landing and went up a little so I just took it easy, went up, and tried a couple of times until it final realized it was on the ground. It's good to know how it figures this out as P2P has shared.
     
  6. SARDG

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    Not a flip in the bunch! :cool:
     
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  7. RichWest

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    Never any....in thousands of flights.
     
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  8. fpvsteve

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    P2P you described it very well.
    A must read for novice drone pilots. Also relevant for other Drones besides Solo.
    Thanks!
     
  9. CanadianSolo

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    Also, temperature will affect your take off. I had a crash, I sent in the logs, 3dr said motor pod. It wasn't i continue to fly with the same pod. When i looked at the logs i saw temperature/barometer off the charts. ----Moral of the story is this: In Winter..... Take bird outside let it sit and get acclimatised 10 min then power on and take off.-- I took off too soon and it tried to re position and flipped right on its back.
     
  10. Pedals2Paddles

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    @RichWest, did you actually edit together a landing compilation for this? lol. I wish I had your free time! :)

    @fpvsteve, I was very used to landing my other arducopter birds in stabilize. Down/left disarmed 100% of the time. Never heard of such an issue until I started flying the solo and joined these groups. With the solo, I had to actually go read up on how it it supposed to behave when landing in loiter and alt hold. I never bothered before.
     
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  11. RichWest

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    No and it wasn't meant to discount your post warning of landing hazards. All points you made were valid, thank you for taking the time explain the various conditions. Just adding content examples of landing, very few videos showing actual landings. My apology if you were offended in any way, was not my intent.

    Seems people have little clue on the art of landing in a variety of situations and are scared to practice. It is the most difficult procedure for any flying craft, toy sized or full sized. I put the video together a few months ago when it was recommended to only land in Fly:Manual. Hogwash. I recommend to new pilots to practice landing over and over. Touch and go's, just like any pilot training. They learn quickly nose into the wind provides better landing control. Especially with Solo's longer stance and weight distribution front to back. Not intuitive unless shown first.
     
  12. Pedals2Paddles

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    I didn't find the video insulting. lol. I was merely commenting on a landing compilation video. It was entertaining.
     
  13. Rich

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    Petals, you mentioned that holding down and left on the throttle stick only applies to stabilize now. Why is this, did they change the firmware? I wouldn't want to start spreading this info unless we knew it was 100% fact.

    As far as I know, holding full down and full left on the throttle stick is the universal command to disarm the motors, with no need to wait for landing detection to kick in. So I'm wondering when and why 3DR would change this?

    I always hold full down and full left to kill the motors and wait for the motors to stop. This way I don't have to rely on only on the landing detection function. It has always worked flawlessly. It's not that only holding the stick down won't work, but my thought is that from a pilots point of view it is just as easy to hold the stick down and left as it is to hold it down only and not left, so why not remove the landing detection from the equation. Actually I find it easier to hold down and left as its hard against both stops when it's in the corner of its travel.

    Of course I haven't seen a note in the firmware release notes about a change in the motor disarm function, so I could have missed a change somewhere. If this has changed in the firmware, I'm happy to learn something new!

    Note: I haven't tried this if the copter is flipped and suppose I could test it with the props removed, but I haven't done this yet. It's not an emergency KILL command as A+B+Pause is, but it does disarm the motors with certainty.
     
    #13 Rich, Sep 13, 2016
    Last edited: Sep 13, 2016
  14. Pedals2Paddles

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    @Rich, I used to think down/left applied to all Arducopter flight modes too, but that's not the case. I think older variations it may have, but not anymore. In Loiter (Fly), Alt Hold (Fly Manual), Land, and Auto, it only needs to see the throttle at minimum with the vertical rate close enough to zero (between +20 and -20 cm/s is what it considers close enough to zero). So all you need is the throttle stick fully down when hand flying. When in Auto/Land, the Pixhawk is bringing the throttle fully down automatically as it is trying to descend with the ground in the way, which accomplishes the same thing... throttle at minimum.

    The fully left thing has no impact in those modes. You may think it does, because you do it out of habit and it happens to be disarming when you do it. But it's disarming because the stick is fully down, and the left has nothing to do with it. It only applies in stabilize and I think acro and sport. In those modes, down and left will disarm, period, end of story, no other logic is taken into account. That's why you can always do that to disarm in stabilize even when the accelerometers and baro are having a conniption preventing it from disarming in loiter or alt hold.
     
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  15. Rich

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    I hear what you are saying, but have you seen the firmware change that documents this? Or is it just how we think it works?

    It may be hard to tell without seeing logs or monitoring data to see if down and left is no longer a disarm command in all flight modes.
     
  16. Pedals2Paddles

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    It's not 3DR's modified fork of Arducopter. It's arducopter anything since at least I believe 3.0 or 3.1. Detailed in the Arducopter wikis pages. You have to read several different parts of the wiki to put it all together, which is what I had to do to make sure I got my little guide correct. It's also backed up by the actual behavior... if down/left was the universal disarm, we wouldn't have aircraft landing in alt hold or loiter refusing to disarm :)
     
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  17. Jubalr

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    I wouldn't put alt hold and loiter in the same category of refusing to disarm. I have not seen an instance of motors not disarming in manual. Loiter is a different procedure (internally) completely in that you are relying on the FC to decide that it will shut down the motors as opposed to the pilot telling the FC to disarm. I think it was best demonstrated by @Vegasrobbi in his test video below starting at about 2:00min in. The primary difference and cause of problems in the auto land modes is when setting Solo down on uneven ground.
     
  18. Pedals2Paddles

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    The disarming decision is more or less strict depending on the mode. But the underlying logic and procedure is the same (throttle at minimum only). I couldn't tell you the exact logic tree and how strict. But regardless, it is still just throttles at minimum for loiter (Fly), Alt Hold (Fly Manual), Land, RTL, Auto, and Pos Hold. Stabilize, acro, and sport are the only ones where down/left is the force disarm command.

    Just to make sure, I posed this question on the Arducopter site for the devs to verify. Will advise and update if needed.
     
  19. Jubalr

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    Yes, they certainly may have modified the behavior in different modes. But it would be easy to duplicate @Vegasrobbi tests on the newer FW versions. I have always been wary of down and left while flying in man,acro & stabilize not confident that it couldn't kill the motors in full descent with a little yaw input. I'm sure they are checking the baro readings before killing the motors, but just something I try to avoid. But nevertheless, I will continue to land in manual/stabilize and not rely on the FC for full landings. YMMV.
     
  20. Pedals2Paddles

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    I think that would actually disarm it in flight. I seem to remember reading about some brave soul who climbed up "very high", disarmed using down/left in stabilize, let it fall a few hundred feet, then rearmed while it was falling. And it actually did manage to level itself and arrest the descent with full power applied. Long time ago, so I could be nuts, or the coding could be different now. But none the less, I avoid that stick position in flight like the plague too.
     
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