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Now a 'calibrate everytime' believer/ these birds are tough

Discussion in 'Phantom 2 Vision + Discussion' started by tejano, Aug 6, 2014.

  1. tejano

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    I went back to same practice spot as the day before. After reading in several places re-calibration isn't necessary if you are close to where the previous flight was, I skipped the step. I had a nice vertical takeoff to about ten feet. Then, on its own, the Phantom tilted to the right and accelerated to 20mph+, flew about 100' and crashed into a tree, bounced off, flipped over, and dropped from about ten feet into several inches of pine needles. I heard the motors whining and immediately cut power.

    BTW, these Phantoms are tough. Cleaned all of the debris from the Phantom, replaced two props, CALIBRATED, and she flew fine for two batteries worth. Whew!
     
  2. DaveTown

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    Re: Now a 'calibrate everytime' believer/ these birds are to

    Too bad about your crash. Glad the bird is ok. Somehow though, i dont think the crash was necessarily related to 'calibration'. I got my Phantom last Christmas, and have flown it nearly 200 times. I fly in a lot of different areas, though all in the few counties around my home. I have calibrated the compass exactly once, the first time i brought it out to fly. There is no need to calibrate the compass every flight. Period.
     
  3. BJames

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    Re: Now a 'calibrate everytime' believer/ these birds are to

    I do it when I go 30+ miles from my previous cal spot. I kinda agree with Dave in that it likely doesn't need it. And with the latest firmware fix to address the variance that I have to live with all is working great!
     
  4. slothead

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    Re: Now a 'calibrate everytime' believer/ these birds are to

    I'm with BJ, my last three flights have been from my yard and I cal'ed it once (prior to that I was 50 miles away), and haven't done it since. I prefer this because I feel pretty silly dancing around in my backyard with a hunk of plastic and metal. :lol:
     
  5. tejano

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    Re: Now a 'calibrate everytime' believer/ these birds are to

    I always look around to make sure no one is watching before doing the Phantom cha-cha.
     
  6. slothead

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    Re: Now a 'calibrate everytime' believer/ these birds are to

    Considering your username, I'd call it the Mexican Hat Dance! :mrgreen: --- edit --- Or maybe the Tex-Mex Hat Dance! :lol:
     
  7. dannytroy

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    Re: Now a 'calibrate everytime' believer/ these birds are to

    I wonder if you have a failing ESC. I had a similar occurrence and attributed it to a bad ESC. I know there are motor upgrades, but I would like to see an ESC upgrade. I'd bet the Phantom ESC's are no more than average grade.
     
  8. TeeJayN

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    Re: Now a 'calibrate everytime' believer/ these birds are to

    Well, that's your opinion. Period. The compasses are very delicate and easily affected by proximity magnetism. Hook your bird up to the Assistant to monitor the compass. Then take a 6x9" car speaker and place it about 1 foot away and see how much it changes. Now, how do you know that every Phantom owner happens to transport their bird no where near a car speaker? Just because you have not had an issue doesn't mean others, unknowingly, might create a problem with the compass during transport.
    Calibrating the compass is simple and quick, and In my opinion, should be done before first flight at any location. It's an extra measure of cheap insurance.
    Your mileage might vary.
     
  9. rrmccabe

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    Re: Now a 'calibrate everytime' believer/ these birds are to

    I think the calibration is a good idea.

    But in my opinion what happened does not sound like its related to a compass calibration.
     
  10. Mako79

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    Re: Now a 'calibrate everytime' believer/ these birds are to

    Sounds like the IMU was out of whack.
    An IMU calib may have been the fix.
     
  11. JWarren

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    Re: Now a 'calibrate everytime' believer/ these birds are to

    I took my Phantom out to my backyard the day before yesterday, calibrated and flew. Went to the same spot yesterday, even the same take-off spot, had TBE and after flying the Phantom told me the compass needs calibration. I think the more the calibration the better, especially with the new push button feature. Period.
     
  12. DaveTown

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    Re: Now a 'calibrate everytime' believer/ these birds are to

    You're right, I certainly can't account for every misuse that an owner could subject his Phantom to. But with reasonable care, there is no need to calibrate the compass before every flight.
     
  13. slothead

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    Re: Now a 'calibrate everytime' believer/ these birds are to

    That's a good point TJN. I keep mine in the trunk of my car a LOT! And although I have not checked, I'll bet there are a couple big speaker magnets mounted on that shelf under the rear window - right above the trunk! I wonder if it would be a good idea to get a gauss meter (whatever they are called these days) and assess the environment there.
     
  14. N017RW

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    Re: Now a 'calibrate everytime' believer/ these birds are to

    Compass compensation is primarily to characterize the hard and soft-iron distortion created by those items within the a/c that move with it.

    I have traveled 600+ miles and not needed to re-compensate, but as soon as I replaced the OEM radio system it was immediately apparent it was needed due to the internal h/w changes.
     
  15. Meta4

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    Re: Now a 'calibrate everytime' believer/ these birds are to

    The elevator button allusion is perfect.
    The calibrate every time school of thought is based on:
    • fear of losing control of the Phantom
    • a lack of knowledge of how the Phantom works
    • a desire to do something and
    • the concept that if something is good then more of something should be even better.

    It's the same principle used by the ancient Mayans who sacrificed a virgin each day to ensure the sun would rise the following day. It's superstition driven by fear and ignorance.

    Calibration of the compass is necessary because of magnetic declination which is the difference between magnetic north (based on the Magnetic North Pole) and map north (based on the True North Pole. Declination is different for different locations and maps are available to show what your local declination is.

    You have to calibrate the compass in your Phantom because it was assembled in Shenzen, China where the magnetic declination is -2° and it has been calibrated and tested there. When you take your brand new Phantom out of the box at home the declination is likely to be something different. The Phantom needs to know about this so that it can allow for the magnetic variation and know where it is flying and how to get back to its home point.

    An error of 1° is not likely to make much difference but an error of 10° or more would be significant. Looking at maps of magnetic declination you can see how far you would need to move to make a significant difference. Thirty miles won't make any difference unless you fly very close to one of the magnetic poles. If you travel along one of the contour lines of the mag. dec. map you could travel quite a long way and still have the same magnetic declination. For example from Minneapolis to New Orleans or Norway to the Congo in Africa.

    Here are some maps showing how magnetic declination varies across the earth. Understand your Phantom and fly better.

    [​IMG]
    [​IMG]
     
  16. rrmccabe

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    Re: Now a 'calibrate everytime' believer/ these birds are to

    ^^ Great info. Thank you.
    Guess I am be lucky to be in the midwest and in an area where I have to go a long ways.
     
  17. Mako79

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    Re: Now a 'calibrate everytime' believer/ these birds are to

    +1000. You are spot on!

    The DJI app should have the same info as the Phantom assistance to show MOD values for both compass and IMU. I am sure it can do this as the FPV telemetry shows speed and the warnings appear when the compass needs calibrating.

    On a side note, I'm on the eastern coast of Sydney Australia. Declination of 10degrees. TBE and J hooks galore and I could never fly straight. I heard people in New Zealand had declination of 35 which made their phantoms crab walk. Didn't matter how many times they calibrated the compass. Thank god for 3.06.
     
  18. cahutch

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    Re: Now a 'calibrate everytime' believer/ these birds are to

    My understanding is that the calibration process also allows the system to account for and cancel out static sources of magnetic interference.
    From things such as a camera or gimbal hanging near the compass or other metal parts and DC current sources nearby.

    You can't calibrate for moving sources of course but those things inside and attached to the Phantom that create or alter magnetic fields are static in relation to the compass sensor.
    The calibration process allows the system to see how the magnetic fields change during rotation in the earths magnetic field while all other magnetic sources nearby move with it and so remain stationary in relation.

    So in my mind, it's important to re-calibrate the compass if you added or removed any metal or electrical devices or any object attached to the Phantom.
    This could include the battery which would be strong source of magnetic field due to the high DC current that flows through it.
    Though I'm sure there is little to no difference in the field produced by different batteries, I would certainly re-calibrate if I was attaching or removing a camera from one flight to the next.

    Or am I mistaken in this understanding? The DC current from the battery and motors should create very strong magnetic fields and the system would need to compensate for those.
    A camera handing on a gimbal near the compass has metal parts and electric current running through it and will certainly affect the compass reading.
     
  19. Clipper707

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    Re: Now a 'calibrate everytime' believer/ these birds are to

    Is there any harm in calibrating every time? Question mark.
     
  20. cahutch

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    Re: Now a 'calibrate everytime' believer/ these birds are to

    It's just occurred to me that this must be completely wrong.
    There's no way to calibrate for declination.
    The compass can tell what direction is magnetic north but the phantom has no way to tell what's true north. So there's no way to compare true north to magnetic north.
    There must be a lookup table for declination that has offset values for different geographic regions.