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How important is center of gravity on camera position?

Discussion in 'General Discussion' started by sehested, Jan 29, 2014.

  1. sehested

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    Im in the middel of designing a new camera mount so i could fly with a Ixus 510, and might RX100M2 in the future. My initial thought is to use the Zenmuse anti-jellow mount and design a topplate for this with a GoPro mount. Problem is that height of camera is very close to hitting the bottom.

    Question is would the flight performance be badly influenced if the camera below is not perfectly centered? By shifting it a bit to the side it will be possible to have micro servo for shutter release mounted on top with hitting the Zenmuse anti-jellow mount.
     
  2. gbshovel

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    I would think a lot! I noticed just adding an carbon fiber anti-V camera mount to the Phantom made it want to lean forward on takeoff. A well balanced rig has got to be easier on the motors and everything else.
     
  3. Shrimpfarmer

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    I don't know is the safe answer however I would imagine that the quad would apply more power to the heavy side to lift it level. Wiser minds may have a different view.
     
  4. LandYachtMedia

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    Balance is certainly important. If you have an option to adjust the COG without adding more counterbalancing weight then you should. It will improve flight performance for sure.

    When my wireless and iOSD setup arrived I took a lot of time on the scales to figure out the best place to put it for balance and aerodynamic effects from the props. With just a few grams of cross weight difference the machine flew and hovered very well. TOW was 1305g.

    I'll be going through the exercise again when the replacement machine arrives. I'll snap some photos of the process and how it turned out. I'm considering stripping the iOSD and video transmitter down to their bare parts to reduce their weight. Also might remove the CANBus cable on the leg and put the naked mini iOSD module inside the shell.

    I weighed the GoPro/Gimbal, transmitter, and mini iOSD. They total 285g. It was more than I expected holding all the parts in my hand at one time.
     
  5. sehested

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    If the center of gravity have a big impact on the flight performance, why is the mount underneath the Phantom then positioned in the front and not in the center? It offcourse gives better pictures when you use wideangle on the GoPro so you dont get the landing gear in the shot.

    On small compact cameras the lens is normally not in the middel of the camera. Should you go for center of the lens or center of the camerabody?
     
  6. LandYachtMedia

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    In a perfect world yes you would mount the center of mass of the gimbal (with camera attached) to balance the CG of the craft. I suspect they made that decision with the Phantom expecting most of us to add a video downlink which will balance the weight out. The addition of the camera downlink and mini iOSD brought my cross weights to within a couple grams.
     
  7. ElGuano

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    Once in the air, even quite unbalanced heavy quads don't really phase the Phantom--it's constantly adjusting in any case and bevhaes indistinguishably from a fully balanced quad in regular flying. I've also timed flight time and voltages for a perfectly centered quad and one with 200g hanging off the front, back, left, right, bottom and top. There is zero difference in flight time in any of the above setups, so I don't think the motors on the heavier side are working significantly harder to keep the Phantom in attitude in ordinary imbalance situations.

    On takeoff, you can certainly have a bit of lean towards the heavier side--the Phantom doesn't know and can't compensate for balance until it's in the air.
     
  8. LandYachtMedia

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    Where it will come into play is in total lift capacity. An off center CG reduces the total lift capacity (will certainly affect rate of climb and power to arrest a decent). That is due to the motors on the heavy side reaching full capacity early and leaving the motors on the light side with power to spare leading to an overall reduction in "area under the curve" of power.

    Since motors of this type have a pretty flat efficiency curve over their developed power range it won't affect run-time much. It will however affect the total amount of vertical thrust the craft can produce while staying level.
     
  9. LeoS

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    Thanks for the enlightenment :)

    What is the easiest way to weight\determine CoG on a Phantom?
     
  10. LandYachtMedia

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    I used a kitchen scale with a little platform around it of the same height as the scales platform. This is important. The phantom must sit level across the scale and the adjacent support platform for the weights to have meaning.

    I weighed each of the "pads" on the landing gear one at a time. That will give you the relative weights of each corner. From there I moved the transmitter and iOSD around on the velcro on the bottom of the Phantom till the weights were nicely similar.
     
  11. Shrimpfarmer

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    That is a neat trick !
     
  12. LeoS

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    Thanks for the tip!

    I had something like that in mind (pads: right pair, left pair, front pair, back pair) to get a rough distribution along x and y; but I forgot about levelling them properly :shock: