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Negative Altitude

Posted by Les M on March 3, 2013 at 10:20pm

Hi Everyone,

Have a 2.9.1 quadcopter which flies really well in stabilize mode but when I attempt to use Loiter or RTL, it takes off at maximum climb. It's easily recoverable by switching back in to stabilize mode again but don't know whats wrong. Also, when it takes off, the first few metres seems to read the altitude correctly (sonar maybe?) but as soon as it gains some height the altitude soon goes negative. The altitude seems to be correct, but negative values. I am new to RC in general but I am thinking the neg altitude issue may be related to the loiter/RTL problem?

I do have sonar fitted which I have tested in the CLI and it is working but I have tried with the sonar on and with it off and makes no difference to the behavior in loiter/RTL mode.

Thanks,

Les

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Replies

  • Usman Qayyum July 8, 2013 at 3:23am

    This problem happens to me as well. The baro shows negative values. The reason behind is vibration as pointed out earlier. The ardu uses Accelerometer z-axis (up/down) values in conjunction to sonar (<11m, if enabled) and barometric for altitude hold. 

    Please have a look at the sonar/baro logged data (on ground both are similar while flying due to vibration, baro shows negative values)

    Another reason sometime of baro erratic behavior is:  the temperature fluctuation and wind pressure changes (proper covering is recommended, plz have a look at this: http://diydrones.com/profiles/blogs/protecting-apm2-5-baro-sensor)

    baro and sonar_data.png

  • Les M March 9, 2013 at 3:56am

    Hi Guys,

    Tried putting the APM on to a foam pad, also loosen'd the wires going to it. Checked that the foam block is inside the APM (yes it is). Result is I took it out today and it performed absolutely the way it should. Alt hold, loiter and RTL performed really well except vert landing speed in RTL is a bit slow...

    Thanks HEAPS for your help everyone!!

    Les

  • T3
    Ted Van Slyck March 7, 2013 at 10:28am

    I crashed in some snow today and the APM got wet. I dried it out and when I plugged into Mission Planner I noticed the altimeter was showing something like negative 2 million. I did the CLI test altitude and it was outputting normal numbers, +/- a few centimeters.  So I erased EEPROM, reloaded 2.9.1, and re-input my config settings and viola!  Fixed. Maybe a drop of water got on my baro and I needed to reset things after that egregiously bad data? Not sure

    Ted 

  • T3
    Richard Boyhan March 4, 2013 at 6:29am
    Before you try loiter or RTL, you need to see if altitude hold works. All advanced flight modes use altitude hold as a base. With RTL, the copter should climb to 15 meters and return to launch point. You must have GPS lock for RTL to work. Leave sonar off, it is not needed for altitude hold.
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