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Flying below home altitude - RTL mode

Posted by Raúl Edo on April 10, 2014 at 5:30am

Hi everybody,

I've been searching but haven't found anything certain about this.

Well, the question is... How Arducopter handles negative altitude values? I mean, what would happen if I arm (and consequently lock home position and altitude) my copter on the top of a hill (or building) and then I fly it to a point below this home position (imagine 300 meters below it)? Would be any problem with the negative altitude values It would "read"? 

And also, assuming there wouldn't be problems with that, If I switch to RTL mode while my copter being at e.g -150 m, would It fly up until reached the desired RTL altitude (meaning in this case 150 -to get home- + ALT_HOLD_RLT meters)??

I'm a bit confused about that and don't want just to try it out and check what happens...

System details:

Arducopter (Quad) v 3.1.2

APM 2.6

Mission Planner 1.2.97

Thanks in advance. Any tip would be accepted.

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Replies

  • dr0n3droid April 10, 2014 at 9:56am
    I've never been 300m below home, but 70-100 without issue. You're assumptions are correct. Home is zero and negative altitude is just fine. RTL above home alt.

    Mike
    • Raúl Edo > dr0n3droid April 11, 2014 at 12:20am

      Hi Mike, thanks for your answer. It's fine to know that.

      Another doubt I have and maybe you could know the answer is about negative waypoints values. I know that when setting ALT_HOLD_RTL parameter to negative values makes the copter to hold current altitude in RTL mode, but don't know how It works on normal waypoints. 

      In the previous example (top of the hill), will the copter fly down below the home altitude if I set an altitude value under zero? What about the follow-me feature? Will it work properly in that assumption?

      Thanks for reading!

      • dr0n3droid > Raúl Edo April 11, 2014 at 1:38am
        I haven't tried negative altitude WPs in a mission. Unless there's something in the code to prevent neg. WPs for safety reasons, I suppose it could work.
        Another thing I haven't tried but is worth considering is Verify Height in Mission Planner. It uses Google Earth topology. So in theory it should hold altitude above current ground level rather than using home as a zero reference. Maybe it will work with FollowMe also. How close to to ground do you plan to fly?
        My copter is a too bit shaky right now for any AUTO flight modes. I've slammed it into the ground a few times recently. ACRO mode is awesome!
        If it's not too windy I'll try a few things this weekend.
        I do expect to see an updated FollowMe soon. Possibly Pixhawk only.

        3DR GPS/MAG going on my helmet.

        Mike
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