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Naza GPS orientation settings

Discussion in 'Other DJI Multi-Rotors' started by discv, Apr 25, 2014.

  1. discv

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    Given that, on a Flamewheel at least, the GPS is way above the centre of gravity- should the Z axis setting be a positive or negative value?
     
  2. Uncle Meat

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    Negative setting. I have a very tall folding GPS mast on my F550 and with a big old 6400mAh battery slung from the bottom my COG Z axis setting is -27cm.

    U.M.

    [​IMG]
     
  3. discv

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    Nice one Uncle.
    Looking at your quad, the gps is centre of the X and Y axis, yes?
    And therefore the settings are zero ?

    Suppose your GPS was at the back of the quad. Would that make your X axis positive or negative?

    Many thanks for your trouble.
     
  4. Uncle Meat

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    The settings are all based on the relationship between the GPS antennae and the COG of your multirotor. To set it up right you first need to find the COG of your quad or hex. The X, Y, and Z coordinates are the offsets between the antennae and the actual COG of the multirotor. Having my battery mounted slightly rearward causes my COG to shift to the rear. That means my "X" axis will be negative. If my battery was mounted more to the left side of the multirotor causing the COG to be left of center would require me to use a negative number for the Y axis.

    On my F550 the COG is low, rearward, and to the left a bit so MY settings look like this:

    X = -2
    Y = +2
    Z = -27

    U.M.

    Maybe this chart will help you understand.

    [​IMG]
     
  5. discv

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    Great stuff thanks.
    All that remains........ the X and Y axis is a simple balance on rods type of thing. But the Z axis- is that decided by an educated guess?
     
  6. Uncle Meat

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    A little from column "A", and a little from column "B"! I flipped my 550 on its side and used my finger placement on the frame to find the balance point to gauge the COG as it relates to the Z axis. Not real scientific, but close enough to keep the Naza happy!

    U.M.
     
  7. discv

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    Many thanks. You talk a lot of sense in a language I can understand!
     
  8. Uncle Meat

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    No problem! Many people get confused when they make these settings. The most common mistake is assuming the COG of your quad or hex is dead center of the frame and then subsequently entering the numbers based on this. This is rarely the case once you add on the battery, camera, gimbal, FPV, etc...

    U.M.
     
  9. discv

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    Sorry to bring this up again. I wrongly thought i had it clear in my head. But alas..


    With the top plate and battery fitted my CoG is 2cm above the arrow on the Naza [all 3 axis]

    So the GPS is 5cm forward of CoG.
    the GPS is 5cm above the CoG.
    The other way [the x axis?] the Gps is bang on.

    HELP!
     

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  10. Uncle Meat

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    So your 450 is perfectly balanced dead center 2cm over the Naza module with everything installed and bolted down, correct? If that's the case it makes things simple. The thing I need to know is the distance (height) between the GPS puck and the COG. That will determine your Z axis.

    U.M.
     
  11. discv

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    "So the GPS is 5cm forward of CoG.
    the GPS is 5cm above the CoG.
    The other way [the x axis?] the Gps is bang on" Quote

    Is more needed than as posted Uncle Meat?

    What's confusing me in your example of your own quad is the y=+2. With your CoG being to the left of the GPS.........or are you viewing from the front?
     
  12. Uncle Meat

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    Don't let my config confuse you. I had some components mounted off to the side of my frame which moved my COG. You do not have this issue though. So lets run down what you do have and what the initial settings should be.

    GPS is 5cm forward of CoG: X = 5

    The other way [the x axis?] the Gps is bang on: That would be the Y-axis. Y = 0

    GPS is 5cm above the CoG: Z = -5

    U.M.
     
  13. discv

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    Thanks UM. I wasn't as confused as I thought!

    You have confirmed the numbers I had come up with. Thanks again.
     
  14. Uncle Meat

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    Please let me know how your first flight goes. Pay attention to how straight it lifts off and whether it hovers with no drift. Now that I think about it... Have you adjusted your GPS puck to compensate for the magnetic declination of your current location? Then again, being in London you are already very close to true north with the puck's arrow pointing straight ahead. If anything you could turn it anti-clockwise just a hair (1° 5' 57" W), you are only 1 degree off true north. http://www.ngdc.noaa.gov/geomag-web/#declination

    U.M.
     
  15. discv

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    UM, heavy rain and high winds for the next week in London- maiden flight delayed.

    However, whilst trying to understand this GPS thing I have been writing [and correcting] a blog.

    Before I credit your good self for the help you have given- if I may- could you please check it.

    http://forums.multicopterpilots.com/entry.php?b=16
     
  16. Uncle Meat

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    You'll have to cut & paste it into a PM and send it to me. I can't access your "draft" posts over on those other forums. I would need an account just to see your post. Just copy & paste it into a pm and send it to me here.

    Thanks.

    U.M.