Forward Flight Altitude Loss.

I've been troubleshooting Altitude loss in primarily forward flight. Left or Right roll into a wind results in the same altitude loss as well as being more pronounced when flying into the wind in forward flight. Backwards flight seems to not suffer altitude loss or not to the same degree. 

I loose about 10-15 feet of altitude when this happens. It recovers the altitude when I release the sticks and resume hoover

The only other symptom I've noticed a small yaw when transitioning to forward flight which I believe to be unrelated. 

My configuration is a DYS D800-X8 on Xrotor 40a spinning 4114 400kv 15*5.5 props. Running Pixhawk 3.2.1

So Far I've:

1) Turned EKF Off. - No Change

2) Tried a Softer Foam Mounting scheme. - No Change

2) Increased AV_TC_Z to 7 - No Change

3) Moved Pixhawk from top plate to a lower plate below the frame - No Change.

when I look at the logs I see the barometer indicating an altitude loss while the ctun alt remains relatively constant. But I could be reading the logs completely wrong.

I'm certainly running out of ideas on my end. I'm willing to donate / pay for help. My other option is to go to the Tarot FC or worse a DJI WKM or A2.

Log from today: https://drive.google.com/file/d/0BxqY72fFHLgmdDNfWDV0ZVZibFk/view?usp=sharing

Screen Shot 2015-06-28 at 2.12.12 PM.png

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Replies

  • Here are 2 more discussions of the issue:

    http://www.rcgroups.com/forums/showthread.php?t=2300970

    https://groups.google.com/forum/#!searchin/drones-discuss/AC3.2rc2$20Altitude$20loss$20after$20forward$20fli/drones-discuss/6lJ5M5OR-pw/Ilwo-tAh_IsJ

    There may be additional fixes suggested within.

    George

    • (the second link won't copy correctly. Highlight the whole thing, right-click, 'go to ...')

  • I think you're on the right track re: barometer, Kenneth.

    I recall seeing this problem discussed in detail here and/or on RCGroups.

    Seems X8s in particular have a problem where forward flight causes the copter to fly into a low-pressure zone it creates in front of itself, causing the copter to think it's too high and drop.

    Problem exists for DJi setups too. People (at RCGroups.com) were getting angry at DJI for seemingly ignoring the problem.

    If I recall, there's no easy solution, but someone (DJI?) recommended lengthening the copter's arms to lessen the low-pressure zone.

    Might be wrong on the details, so search away.

    I think Rob Lefebvre was active in the discussions on RCGroups (and I think he was pessimistic about a solution).

    Good luck,

    George

    • Last point: it was people using DJI controllers on their own airframes (I think DJI doesn't make X8s) who were discussing the problem on RCGroups.com.

      George

      • I've been making progress on the issue. Referencing http://diydrones.com/profiles/blogs/loss-of-altitude-after-horizont...

        I've isolated my barometer and have been flying with it located at different spots. I'm able to fly in forward flight into a wind with out altitude loss. Rolling left and right still causes an altitude drop but I'm re working my static port design, Moving the air line to the rear as shown in the post above. 

        I've also been experimenting with placement. Below is the static port located in the front of the aircraft. So far this has given the best results. Below is a picture of the static line coming from the pixhawk case

        3702706718?profile=original

        3702706650?profile=original

    • I'll hazard a guess that another approach might be to try to elevate the flight controller (and barometer) a little more out of the plane of the rotors (this might also have been among the recommended fixes).

      George

  • Graph of flight from today
    3702037587?profile=original

    • Am I chasing the right path with the barometer, Or could the source be a bad Accel, IMU config or something else. 

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