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Unexpected drop in altitude

Discussion in 'Pro/Adv Discussion' started by Jay Pee, Dec 31, 2015.

  1. Jay Pee

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    Hi there,

    Just got my P3 a few days ago, and have been loving it so far. I've done a few flights in wide open spaces with it, and taken it over some mountains and the ocean, recording some cool video.

    I was just in my backyard, trying to hone my flying skills a bit. I turned the P3 on, and did a GPS calibration, before taking off and bringing it up to about to about 10 feet in the air. I then rotated it about 90º with the left controller, and flew it sideways with the right controller. I stopped the right sideways motion. I then started walking to my left, and flying left as well keeping an eye on the P3. It was then that I noticed that as I flew left (not touching the right controller at all), that it slowly dropped in altitude from the 10 feet that I started at, to about 3 feet when I stopped my sideways motion. This was over the course of about 40 feet. I raised it back up to 10 ft, and flew it right, and it kept the same level. I flew it left again, and it slowly dropped in height.

    What gives!? Any thoughts or ideas? Is this normal?

    Thanks!

    Jay
     
  2. GreggC

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    Hey Jay,
    You said that you "flew left (not touching the right controller at all)"
    I am assuming you were using the left stick to yaw left and follow you as you walked??
    If this is the case I suspect you inadvertently gave down input to the left stick and did not realise it.
     
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  3. Jay Pee

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    Hi Gregg,

    Thanks for the response. Sorry, I meant that I never touched the "left" controller ... not right. No yaw input, as I was flying to the left, using the right controller. The 2nd time it happened, I made sure that my hand was completely off the right controller, as I wanted to be certain that I hadn't caused the decrease in altitude.

    Jay
     
  4. Shammyh

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    When in doubt, imu cal and throw in a controller cal for good measure.

    After that, repeat the same circumstances and report back.
     
    Jay Pee likes this.
  5. Jay Pee

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    Shammyh,

    I was thinking of doing a IMU cal tomorrow. Not familiar with the controller cal, but I'll look into it too.

    Thanks!

    Jay
     
  6. Shammyh

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    Be obsessive in your imu cal too.

    I use a textbook, level it (with Phantom in place to mimic weight distribution) with a spirit level and paper shims, and don't bump, move, or even tread heavily near the P3 while it's calibrating. Make sure back to front, side to side, and corner to opposite corner are all as level as you can get them.

    Contoller cal is also found within the dji go app, and basically is like a "game pad" calibration in Windows if you've done one of those before.

    After all that's complete, I'd be surprised if you have any issues.

    There is always a little variability in the height while moving around, but shouldn't be more than a meter.
     
  7. Stealth Tours

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    Could there be an issue being at that height where VPS sensors are handing off to GPS. I know you are just getting started with the learning curve....at some point you can hover while pointing the camera straight out, switch from "P" to "F" mode, select "course lock" which allows you to yaw the quad along with what you are focusing on, pushing the right stick forward makes the quad go away from you, pulling back does just that and right and left does just that no matter how often you yaw.
     
  8. alokbhargava

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    When you are within say height of 10', GPS doesn't maintain height. Height is maintained by VPS ( if enabled) and thus if the ground is not flat, height will be adjusted accordingly. Be careful if you see a step on the route when flying low.
     
  9. PVFlyer

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    This sounds to be discrepancy after heating up barometric altimeter in IMU if you turn off VPS, especially many people do cold IMU calibration. We remind Mission Planner users on autonomous flight Important Notes, though this also applies to normal flight.

    • Aircraft height (altimeter) may easily vary 15-20m (50-66ft) off the actual height after aircraft flying and heating up several minutes. You are recommended to let IMU warn up properly on the ground especially in cold weather, and set waypoint height minimum 25m (82ft). Cold IMU calibration trick is NOT recommended which might incur more discrepancy in altimeter reading.

    For example, if there is a tree 30m height and you set the first waypoint to 40m above that tree to maintain a 10m gap and the last waypoint is also set to 40m above the same tree after 10 minutes mission flight. The aircraft might reach the first waypoint well above the tree, but when it reaches the last waypoint 10 minutes later, it might hit the tree due to discrepancy of barometer though the altimeter is still reporting 40m height.
     
  10. Shammyh

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    Very good points. Though I doubt it applies in this case, as he's a new flyer, and I doubt has started with a "cold imu cal" before his first couple flights.