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Compass Error - Near Disaster

Discussion in 'Pro/Adv Discussion' started by Tim_alabim, Nov 16, 2015.

  1. Tim_alabim

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    New flier here. I have had the P3A for a couple of weeks and have have a half dozen flights under my belt. Yesterday I was doing a few over water flights driving in my truck a couple of miles between 3 different sites. First two flights were flawless. On the 3rd, I had just taken off and luckily, before I got out over the water, the copter started behaving erratically. I noted a compass error in the app. It was bit windy and was quite difficult to land but I did manage without tipping over. I had the VPS off as suggested in several posts here. I think it would have been easier to land if VPS was on, perhaps? I had calibrated the compass just before each of the first 2 flights, but didn't just before the 3rd as I had driven just a couple of miles from the 2nd site and didn't think it was necessary.
    Thoughts on what could have caused the compass error? I'm taking as a lesson learned and will calibrate prior to every flight going forward.
     
  2. bbfpv

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    Metal?
     
  3. III% Streve

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    The more you do a compass calibration the more likely you are to have a BAD compass calibration. As anything, the more you do it the more likely an error will occur. As for VPS.. if its on it will act a bit stupid low over water. With it off.. it will act bit stupid low over water. You almost always take off from land, where VPS does its job. So why ever turn it off? Its far safer to simply not fly below 3 meters of the water surface!
     
  4. Meta4

    Meta4 Moderator
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    Hard to say what caused the error for sure in your case but the most common cause is calibrating the compass in a bad location where the earth's magnetic field is distorted by a large mass of iron or steel - like on concrete with steel reinforcing.
    Calibrating in those environments effectively zeros the compass so it reads north with the distortion .. then when you fly out of the area affected by the steel, your Phantom's compass is now screwy because of a bad calibration.

    You definitely do not need to recalibrate the compass every flight and making frequent and unnecessary recalibrations increases the chance of getting a bad one.

    This thread gives a lot of info to help you understand what calibration of the compass is all about.
    Compass Calibration, A Complete Primer | DJI Phantom Forum
     
  5. Wibble

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    Hand catch - much better especially when windy.
    Hand catch is not really the right term. Hover and grab would be better - reach up and grab a skid. Left stick down until the motors stop.
     
    bobmyers likes this.
  6. m4dp4rrot

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    Were you standing near your truck when you calibrated the compass? It is extremely sensitive and even being within 10 feet of such a large amount of metal can throw it off. I tried to take off from a picnic table just a few days ago, but every time I put it down, COMPASS ERROR. Wondering wtf is going on, I finally look under the tabletop and there are two big 5 inch dia metal pipes supporting it.
     
  7. Tim_alabim

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    Thanks for the tips and link to the "Compass Tip" Thread. Very helpful. After reflecting, I do believe I may have been too close to my truck when calibrating. Lesson Learned!!
     
  8. GadgetGuy

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    Better yet, once you get a good compass reading, leave it alone!:D
    Unless you are flying more than 100 miles away from your last good compass reading, there is no reason to recalibrate your compass, and there are a thousand reasons not to! :eek: