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How critical is CG?

Discussion in 'General Discussion' started by e2cmech, Dec 12, 2013.

  1. e2cmech

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    I added a brushless gimbal to my Phantom and noticed it is nose heavy, just wondering how much, if any, is acceptable? I am thinking about adding a small 3S lipo to power the gimbal and mounting it to the rear of the vibration mount to offset some of the imbalance. Should I not worry about it? Thanks!
     
  2. OI Photography

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    Rather than adding extra weight to offset that imbalance, you can adjust the settings in the NAZA to reflect a shift in the CG, and then the Phantom will adjust for it automatically. Power consumption may be a little higher that way than without an imbalance, but probably not as much as it would take to lift the weight of the extra battery you were thinking about.
     
  3. ElGuano

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    I don't think it makes sense to use extra batteries for low drain items like gimbals and VTX. If it lasts longer than one flight you are carrying dead weight. COG isn't super important on the phantom, I've tested it extensively and it doesn't really impact flight time or handling. Within a very wide margin of reason.
     
  4. e2cmech

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    Thanks for the replies. I will tie into the main power and forget adding the extra pack. I might see if I can shift the gimbal to the rear a little to help offset the weight and adjust the settings in NAZA.
     
  5. tanasit

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    Would you care to elaborate the statement highlighted?
    I thought the adjustment is for GPS position only.
     
  6. OI Photography

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    Yeah, I was mistaken, I was thinking you could adjust the NAZA's position relative to the CG as well.
     
  7. Hiway

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    When I made my first flight, the Phantom rose as level and landed as level as anyone could ask.

    Once I put the gimbal on, it continued to rise perfectly, and land the same.

    After I tapped a large piece of granite, and the Phantom dropped to the ground nd I replaced 2 props, it listed forward on takeoff, but landed perfectly.

    I also noticed that once the Phantom lifted with the gimbal, that forward tilt corrected immediately once the skids were in the air- which is odd, not to mention the fact that I watched tons of videos with Phantoms carrying gimbals that did not leave the ground with this pronounced forward tilt.

    I discovered one of the props was slightly higher than the others (left front silver tipped prop if you are facing the battery compartment)

    After balancing a new set of props and replacing all of them, and confirming that they were all consistent, I expect the problem to be resolved- I wish I could verify but the winds and the weather have kept me from flying for 4 days now.
     
  8. Fdnyfish

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    did you bend one of the arms?
     
  9. Hiway

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    If that was to me- negative- in fact, despite the odds and since the landing zone where my bird dropped was all soft grass, I didn't even get a scuff on her. I feel pretty blessed.

    Of course, I am hard on things, and once the learning curve of flying has smoothed out some, I will be ordering another Phantom for backup as I know e, and I will push envelopes; or more likely getting a whole other copter as I am now fully addicted to r/c again.
     
  10. tanasit

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    May I suggest do the following test for ALL the props.

    Turn one tip of the prop until it positions right over the shell, then look at the gap or space between the shell and the tip of the prop. This should be about 1/4". Turn the other tip of the same prop to exactly the same position on the shell and see if the gap is EXACTLY the same as the other tip? You will be surprised! ;) ! If not, then either the hole of the prop is off or the motor shaft bend or the motor is not fully seated or combinations of these.

    Some carbon fiber props with untrue hole can be slightly adjusted by filing off the hub material on the high side.

    If you fly with soft and thin after market plastic props, you may want to check the blade tracking just like the rc helicopter flyers do. Defective props will only show this ill effect while the props are spinning, so be careful.

    You can hover at eye level and look at the tips' arc and see if they line up or one is higher than the other. To help visually, you can use the different color Sharpie painted the tips.

    I tried the 3 blade plastic props and found out that the standard black ones, especially with carbon particles seem to have better tracking than the pure plastic color ones. The thinner the blades are the better chance that they will be deformed from the injection molding process, some of which are so obvious that you can clearly see the tips are out of track just by spinning the blades by hand!!
     
  11. ElGuano

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    This is a good test to run. I've always done this with each set of props I have, and found that one of my motor mounts was a tad askew. I righted it by adding a dab of hot glue to one side of the mount.