How to determine where is COG on Z-axis

Discussion in 'DJI General Discussions Forum' started by EgonW3, Jun 19, 2012.

  1. EgonW3

    EgonW3 New Member

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    I've just found quite simple method to detemine Z-axis position of COG:

    1. Determine where is COG on X and Y axis. I think nobody has a problem to find it.
    2. Tilt your copter on the edge of landing skids until you find a balance (copter doesn't tend to flip to right or left)
    3. Make a picture. In my copter green line is where I found my COG on X and Y axies.

    COG.jpg

    4. COG is where red line crosses green line

    What do you think about such a method?
     
  2. eyeball

    eyeball Member

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    I like the idea EgonW3....but I dont think this will give you your Z axis as your will only find the balance point of the copter in relation to the front edge of the landing skid. For example if you were to shorten the length of the skid and redo the same test, you would find the C/G moving even lower down because you would have to lean the copter further forward to the right (off the edge of the table) inorder for it to balance again.
    I may stand corrected... or have understood you wrongly. Good try though!!:apathy:
     
  3. kauaicuda

    kauaicuda New Member

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    I just tie a string to the arms and hang it from a doorway, then the same MS paint lines, works great.
     
  4. EgonW3

    EgonW3 New Member

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    Your bethod is based on idea that when an obiect is suspended, so that it can swing freely, it will come to rest with its COG vertically below the point of suspension.
    My method is based on idea that obiect become unstable when its COG falls outside of the obiect's base.

    Both methods should give the same results, but my method doesn't require a string and because COG is usually quite close to the surface of the arms arms, you get quite sharp angle so it is more difficult to determine it precisely.
    Your method may give you COG position on two axies (by rotating hanging copter by right angle and making another photo).
     
    Last edited by a moderator: Jun 20, 2012
  5. EgonW3

    EgonW3 New Member

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    It will give you the same result despite of edge of base you chose. But in this method it is better to chose the edge that is farthest from predicted COG to achive better accuracy.
     
  6. eyeball

    eyeball Member

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    I understand what your saying, I will have a try of this method later.
     
  7. mitsaras

    mitsaras Member

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    Cool idea, between this and the "suspend by a string" method, it should be quite easy to determine COG along the Z-axis. Thanks!
     
  8. janoots2

    janoots2 Member

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    It's been my experience with the WK that the z axis doesn't matter. When I keep it at the middle of the IMU, my setup is much more solid. I actually tried today to dial in the CG right on the money. My hexa started twitching and swaying. Brought it back down, changed the COG back to the middle of the IMU and it was rock solid again...
     
  9. mitsaras

    mitsaras Member

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    If I understand you correctly, you simply measure the vertical distance from the GPS to the center of the IMU (or Naza, I presume?), and use that as the "Z" value? You ignore the vertical location of the COG?
    Sorry but I am new to this...
     
  10. BorisS

    BorisS Active Member

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    this might help:



    boris
     
    Last edited by a moderator: Nov 22, 2014

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