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Need some ATTI insight

Discussion in 'Phantom 2 Vision + Discussion' started by Pigeon Gun, May 1, 2015.

  1. Pigeon Gun

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    Hello everyone, I'm new to the world of RC flying and drones and really enjoying the reads here on the forum.
    I've recently purchased a new PV2+V3 and am really pleased. I had my only mishap so far on my very first flight, where I hovered a little too long under a tree in my back yard. I guess she lost a few too many satellites and initiated a RTH and got tangled up in tree limbs on the way to the minimum RTH elevation. Broke two propeller guards, but otherwise all was well.
    I build bridges for a living and one of the reasons I purchased the Phantom was so that I could get pictures of hard to see places on completed structures for estimating purposes. I figured that since I knew what would happen in GPS mode once I flew under a bridge deck, that I could simply fly under the bridge in ATTI mode and all would be well.
    Does the phantom need satellite coverage to fly even in ATTI mode? I've gotten about 30 flights in without incident, and feel fairly comfortable with my piloting abilities in ATTI mode, and I know that in ATTI mode the Phantom does not gain the horizontal/lateral stabilization provided in the GPS mode, but will I be able to launch & operate the phantom with little to no satellite coverage, under a bridge, in ATTI mode?
    Thanks for any insight y'all might be able to provide.
    John
     
  2. Jetfixer

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    The short answer is yes, you can take off without GPS lock. Just don't forget that RTH can be initiated by any loss of the controller signal or your low battery setting even in ATTI.
     
  3. N017RW

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    Another caution based on your career statement above, be careful around metal structures (bridges?).
    This will interfere with the magnetometer and cause erratic flight behavior.
     
  4. Pigeon Gun

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    Thanks for the timely responses!
    Points well taken regarding the loss of transmitter signal and low battery initiation of RTH.
    As far as the metal structures go, great point. I was under the impression that while you didn't want to begin a flight from a steel structure or reinforced concrete slab because it interfered with computation of the home point due to the compass being affected by ferrous metal , it wouldn't effect the flight of the phantom once airborne. I can see where electrical transmission lines or radio towers could scramble the signal being received by the Phantom, but after correct establishment of the home point, should the proximity of steel by itself affect the performance of the phantom?
    Thanks again,
    John
     
  5. CoolClownFish

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    Also remember, and correct me if I'm wrong, if you fly without GPS the RTH will not work properly because there was no home point set in the first place. Remember to calibrate it before you fly but do so away from metal structures or electrical such as power lines, train tracks etc...
     
  6. N017RW

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    PG,

    The bridge is not a source of interference per se like the items you mentioned.

    It does however warp and distort the earth's magnetic field around it. This will confuse the MC.

    This is the reason you must calibrate the compass after you add, move, or remove items from the quad.
    This cancels-out the distortion(s) caused by the quad's metallic components.
     
  7. CoolClownFish

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    I'll have to disagree with you. Most bridges are constructed of a large amount of rebar enforced concrete and that will cause interference with the Phantoms compass. I have a concrete pad at work that I can not calibrate it on for the life of me and it has the same rebar reinforcements as a bridge.
     
  8. Pigeon Gun

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    Pretty sure I understand now, and thanks to everyone for the replies. I think what I may try as an experiment is to establish calibrations as usual, away from the structure and metal objects. Then have an accomplice hand carry the Phantom up the slope protection at the end of the bridge and get right in amongst the girders and close to the bottom side of the reinforced concrete deck. Then, while he is holding onto the Phantom landing gear, I'll try to start the Phantom and see how it responds to commands form the controller. That may give me some idea of whether or not my inspection scheme even has a chance.
    I'll report my findings once I've had a chance to see how things go.
    Thanks again!
    John
     
  9. N017RW

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    We actually do agree but you missed the point. It is a 'passive' interference meaning it does not actually produce it's own magnetic field, it distorts the normal field around it.
     
  10. CoolClownFish

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    I must have misunderstood your comment. No biggie.
     
  11. Pigeon Gun

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    I hear ya CoolClownFish. I have the same issue calibrating the compass where I work as well. The property used to be a precast concrete manufacturing plant, and I cannot calibrate on any of the many reinforced concrete slabs on grade that exist on the property. On the other hand, I never have any problem landing on, or taking off again from any of the slabs, as long as I stop the motors prior to re-takoff. It is only during calibration that I have a problem, although the more I think about it, it seems that it should still effect the compass any time it is in the proximity of the slabs.
    John
     
  12. RoyVa

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    Just one note. While flying under the bridge the camera will not be able to be pointed up. Only straight ahead or down. Hope it works out for you.