Hey. I have a quadrotor with Pixhawk, APM:Copter V3.3.3 (acf2e10c). I have tested it in Stabilize & AltHold modes, works fine. Also tried switching to Land mode from Stabilize & AltHold, and the drone lands perfectly.

I wanted to try AUTO mode, as a first test I defined this mission based on the tutorials here:

1. Takeoff to 10 meters

2. Loiter there for 5 seconds

3. Land

I went out for a test, as soon as I raised the throttle in AUTO mode, the copter started climbing VERY quickly, and it kept climbing up until it was about 60 meters above the ground. I waited for like 10 seconds and it kept climbing, so I panicked & switched to AltHold mode. I'm a newbie pilot so I could not control it properly at that altitude and...crash!

I thought maybe it was a bug in my planned mission or a gps glitch or something, so I fixed the copter and tried agian. This time with this mission:

1. Takeoff to 3 meters

2. Land

Again, same thing happened. This time, I switched to Land mode, but it kept climbing like crazy. Switched to stabilize and eventually...another crash.

I reviewed the logs, DAlt (desired altitude) does not match my planned mission altitude (figure below). I have attached the log, can someone please help me with this?

DAlt Plot:


2016-03-10 08-28-02.bin

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    • This is the mounting, under the FC is a thin shock absorbing pad:

      3702622901?profile=originalAnd as for the wiring, almost all of the wiring has been done between the top & bottom plates like this:

      3702622589?profile=originalI am going to make changes in the FC mounting BTW.

  • Stabilize and AltHold do not use GPS.  Auto does.  I'm thinking that your problem is based in your MR thinking that it is somewhere that it is not, and trying to fix that problem.

    Please temper anything that Darius says with a bucket of incredulity and wait for the real experts here to chime in.

    • Even if the copter thought it was in the wrong place (which I don't think could be the case here since I had a fairly good GPS signal & also had set the waypoint radius to 50 meters to alleviate the variations of GPS), I had decreased the default altitude of the planned mission to 3 meters, so it should have tried to navigate to the desired position without going so high.

      And moreover, when I changed the flight mode to Land, it did not make any changes in the behavior of the drone. AFAIK, Land mode does not use GPS nor does it try to move to a specific location, it just descends right where it is.

      Thank you so much for sharing your thoughts. I do hope that the "real experts" will see this topic & respond!

      • "set the waypoint radius to 50 meters "

        Ahah!  A waypoint with a 50 meter radius is a 100 meter diameter sphere.  Anywhere inside that sphere satisfies the FC that it has reached that waypoint.  Try with a 1 meter waypoint radius.  (The larger waypoint radii are used by fixed wing planes that can't maneuver as tightly as MRs)


        GPS Dependency

        Flight modes that use GPS-positioning data require an active GPS lock prior to takeoff. To see if your autopilot has acquired GPS lock, connect to a ground station or consult your autopilot’s hardware overview page to see the LED indication for GPS lock. Below is a summary of GPS dependency for Copter flight modes.

        Requires GPS lock prior to takeoff:

        Do not require GPS lock:

        • A waypoint with a 50 meter radius is a 100 meter diameter sphere.  Anywhere inside that sphere satisfies the FC that it has reached that waypoint.

          Are you sure that the radius applies to the altitude as well?

          Even if it is, this is not the only thing causing my problems because in my first test it was set to 5 meters and the same thing happened.

      • I believe that ALL modes use GPS (even stabilise to some degree), as the onboard sensors (gyros and accels) aren't accurate and consistent enough to hold correct position over time so the pixhawk uses GPS to 'rebase' the sensors, by default 5 times per second.  I'm no expert so could well be talking nonsense but this is how I understand it works.

        As per Land mode, that's an interesting question - I always assumed that once you put it into land it locks onto position using GPS and tries to land on that spot, but have no technical reason to back this up, now you mention it :)

        • Stabilize, AltHold, and Acro don't use GPS at all.  They don't make any attempt to hold position and the aircraft will definitely drift in these modes.  You can fly an APM aircraft in these modes without a GPS attached at all.

          Land mode will use the GPS to maintain position while landing, if possible.  If there's a problem with the GPS, it reverts to Stabilize-style controls so that aircraft will drift, but the pilot can steer it while landing.

          • Unless it's changed recently, if you have a GPS connected then all modes will use it:


            My technical reasoning may be nonsense however!

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          • "Stabilize, AltHold, and Acro don't use GPS at all"

            They do.

            (Although it's true you can fly without a GPS attached.)

            Via EKF, although quite old, see this for the whole skinny: https://groups.google.com/d/topic/drones-discuss/iZmeopHOLGM/discus...

            • Huh, I stand corrected.  So GPS is always being used to more accurately level the aircraft, even when it's not active for position control.  Thanks for pointing that out.

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