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Beginner Questions: First few flights, compass calibration, IMU, FPV?

Discussion in 'Phantom 3 Help' started by rkf3, May 13, 2015.

  1. rkf3

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    Hello! Apologies for these questions that may seem intuitive to the experts!

    I've flown my P3P three times so far. It's my first drone, and I've had a blast. Easier to fly than a 3-axis heli, although the controls and gps positioning are definitely new and I'm adjusting. I have a few questions about stability, IMU calibration, and FPV that are listed below. Cheers for any and all help.

    First, stability. I've noticed that the drone was incredibly stable my first two flights. Before my third flight the controller indicated it needed a compass calibration, and to try to calibrate in a different location. I was on a parking deck and there were a few cars around. I tried in a few different locations and I ultimately found one that worked and I was good to go on the app (full sat connection as well). Took off, 500 feet distance away, 100 feet up, and it noted compass error. It also was wandering/drifting much more than I would have liked. With sweaty palms, I brought it back and landed fine.

    What causes issues with compass calibration? How often should I calibrate the compass? Is a poorly calibrated compass the reason it was 'drifting' more than the flight a few minutes earlier? When calibrating the compass, is it necessary to move the drone itself as indicated in the diagrams, or can I spin myself (and hence the drone)? What exactly is happening in a compass calibration and how does this affect flight characteristics?

    Second, IMU calibration. I haven't had any problems with my video feed or levelness. When should I consider an advanced IMU calibration, and how often? I've seen this discussed a good amount but not explicitly stated.

    Last, learning to fly FPV. I'm comfortable flying FPV beyond LOS or in distant LOS as long as the bird is HIGH. However, objects are much closer than they appear it seems, and the best footage I believe is not overview shots from 200 feet but navigation shots from 50 feet height and a meter or two from an object. What is the best way to learn depth perception in FPV and be aware of distance to objects? This may just be simple practice, but I'm sure some of you pros have an answer for me.

    Again, thanks in advance. I'm loving the drone and excited to proceed (slowly and carefully!) down the learning path.
     
  2. bbfpv

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    Anything metal and potentially anything electronic in the vicinity will cause issues when calibrating the compass. You mentioned you were on a parking deck, I assume that's like a parking garage? If so, there is tons of rebar in that structure, and probably the worst possible place to try a calibration. Yes, a poorly calibrated compass will cause drift. You can move the drone itself, or spin yourself. I personally move the drone, but others do the spin move. Calibration is so the bird knows where North is (to put it as simplistically as possible). You also don't need to calibrate every time you fly as long as you're within the same general vicinity. I recalibrate whenever I'm 10 miles from the last place I calibrated, others say 50-100 miles.

    If there are no problems w/ your bird, don't sweat an IMU calibration. It will tell you when it needs one. Of course if you do any mods to the bird, then an IMU calibration is a good idea.

    HTH
     
  3. Meta4

    Meta4 Moderator
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    bb is right. Concrete has lots of steel reinforcing and that will screw up calibrating.
    Your Phantom wants to know what the local magnetic environment is where it is flying .. not down close to a ton of steel.
    You calibrate where the magnetic field is dominated by the steel and then fly off to where the steel has no effect and things aren't going to be right.

    re FPV navigation .. your camera has a very wide angle lens so it's making things look further away.
    Obstacles are the number one danger and you need to exercise lost of caution near obstacles.
    Trees, buildings etc are the enemy.
     
  4. N017RW

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    The compass does not need to be field calibrated to determine North.

    This is intrinsic to the sensor design and accomplished when deciding the physical orientation of the sensor on the a/c such that the proper reference can be established in the software (X-Y, Y-Z, or Z-X).

    Although it knows which way is North, items in its vicinity can create flux line distortions.
    Calibration removes these distortions created by so-called 'Hard' and 'Soft' iron materials near it.
    Only items moving/rotating with the compass can be calibrated out, or better said compensated for, so this is why you must re-cal when adding, removing, or relocating items in or on your a/c.

    Since the rebar and other materials can distort the ambient mag field(s) and cannot be compensated for (since they do not move with the compass), the calibration fails if the distortion created and measured falls beyond the acceptable distortion limits for which compensation can be applied. In other cases the compensation is applied but when the a/c moves away from this localized interference (distortion) the compensation is no longer valid and unusual flight characteristics occur.
     
  5. rkf3

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    Thanks all, very helpful. The information you all provided regarding technical specifics of compass operation/calibration are helpful and exactly what I needed.

    Anyone else have information regarding how most learn to do FPV? Specific practice techniques? Leaning depth perception based on the drone's camera? I know the answer is just caution and lots of practice, but I'm wondering if there are any practice methods people use to learn the process efficiently.
     
  6. bbfpv

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    When I was learning, I would go to a big soccer/football field and fly FPV to the goal posts like 50-100 ft away. Close enough that I could look up to see how close I was but far enough that I could still use FPV. I would fly toward the posts, then away... eventually I'd be able to get about a 3-4 feet using FPV alone.
    I also put the camera in FPV mode so that I could feel the roll and pitch of the bird in relation to the object I was looking at, then switch off FPV mode when I wanted the shot.
     
    Flyingwulf likes this.