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P3 is heavier on rear end ( battery side )

Discussion in 'Pro/Adv Discussion' started by alokbhargava, Feb 13, 2016.

  1. alokbhargava

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    I carried out a simple test by placing P3 inverted on its top and found that it dips on the battery side which is the rear end of P3. I request some one else to carry out a better test to find out the facts.

    If it's true that rear end is heavier, we may to add balancing weights to adjust its balance and that might give better forward running time per charge.
    ImageUploadedByPhantomPilots1455344052.633056.jpg
     
  2. Kman

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    Could this be why the rear mounting holes are always the ones that crack first? Hmmm
     
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  3. Dirty Bird

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    The motors can handle balancing the load on their own. Any additional weight added will only serve to reduce overall flight time.
     
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  4. alokbhargava

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    In this case rear motors have to work harder to first balance P3 and then still harder to make it move forward.

    Even though we add additional counterweights at the end of the arms, it appears they might improve the overall efficiency. Only experiment will tell us the real facts.

    I would have loved if the front end was heavier.
     
  5. alokbhargava

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    It's true rear motors work harder but it's not confirmed if that's the cause of cracks on the rear shells.
     
  6. Dirty Bird

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    Testing would be interesting. The FC should still be able to compensate & I would almost guarantee it is still more efficient than adding additional weight. In a fixed-wing aircraft being nose-heavy is preferable because it is far easier to control a nose-heavy bird than one that is tail-heavy. I will never forget one of the most harrowing flights of my life flying this twin-engine Catalina. It was the Flight from Hell thanks to an improperly listed center-of-gravity measurement!

    [​IMG]

     
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  7. Noble 1

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    Is there any evidence to suggest the rear motors have more wear and tear from the unbalanced air craft?

    I highly doubt DJI would sell an air craft that was unbalanced enough to cause mounting cracks and motor failure prematurely

    They most likely had research and evidence but didn't feel it was significant.

    I'm under the persuasion that the balance issues are negligible if at all relevant to flight performance. .


    Sent from my iPhone using PhantomPilots mobile app
     
  8. With The Birds

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    Think about moving the camera and gimbke forward. Better work with whats there than add weight. And you may get the skids in the frane less as a bonus.
     
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  9. Chris P Duck

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    Not quite, by adding weight to the front you have balanced it so the load on the motors will be more similar. However if you add weight the back is still lifting the same weight so getting through power at the same rate, the front will be lifting more weight so will be getting through power quicker. Net result, shorter run time.
     
  10. With The Birds

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    Wss the phantom on when the balancebwas checked? Maybe the vamera flopping around came into play here.
     
  11. alokbhargava

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    P3 was off but the camera was clamped into correct position.
     
  12. alokbhargava

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    Not true as the rear motors lift the extra unbalanced weight to P3 to hover.
     
  13. flyNfrank

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    I did some testing on this a couple years ago by finding the center point on the body of the 4 motors. I used a helmet bracket for a gopro camera and used a strong enough string to support the weight. I hung the string from a hanging light in the dining room so I would have to secure anything in the ceiling. I found that aircraft favored one motor more then the other 3, and of coarse having more rear sag due to the battery weight. I then removed the soft cushion feet from the bottom of the landing gear and measured the distance from the table surface to the top of each motor. I found the same motor mentioned above distance was different from the other 3. At that time I came to the conclusion that measurements were different to offset to compensate for the sag.

    After doing this test I tried finding someone that could maybe get into the firmware and adjust the Pitch settings while in full throttle. And I had no luck at finding such person.

    From this point I began focusing on the characteristics of the pitch on the aircraft while in flight by reading the data from the flight logs. Here I found that the pitch is pretty much dictated based on temp. So the only time the aircraft is given max performance benefit is prior to reaching the temp window. At flight the average max pitch angle is -35.

    So now the way the P3 is programmed, you wont be able to add weight or install some kind of wind deflectors that will force flight pitch. The reason is, the P3 reads each of the flight angles and adjust them while in flight to maintain altitude.

    You want to go faster or make the aircraft more efficient, you will need to do it by firmware settings. And since you own the aircraft, it sure seems like you should be allowed to that, huh?

    Btw, my hobby is Top Speed flights with the P3 which is the reason I look for ways to make it fly faster.






    1CP.jpg
     
  14. alokbhargava

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    You seem to have a good understanding of its inner control system.

    Also I agree with your finding that one motor has more sag and nose is up. This is due to unbalanced weight distribution. You are right controls will adjust the angles during flight by adjusting the motor speeds depending upon the stick values. Doing this rear motors will spin faster than needed if there was a perfect balance.

    I m looking at the best solution to get near balance at its expected CG.
     
  15. skyhighdiver

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    How funny we live half a country apart but i notices in your picture We have the same vacuum Odd spot I know ;)
     
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  16. DiluxEdition

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    Interesting. This could explain why the P3 can fly backwards faster than forwards. I was fighting 30mph winds and decided to try going backwards one day when I noticed this..
     
  17. alokbhargava

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    You are right but the problem is Camera can't be turned back :(

    One of the mods one can try by turning the gimbal mount 180deg and go for custom mode for RC sticks.
     
    #17 alokbhargava, Feb 13, 2016
    Last edited: Feb 13, 2016
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  18. Mordor

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    Now i understand why my cracks did appear on the 2 arms....great post!
     
  19. alokbhargava

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    I worked out that we need 5 quarters weight (~28.5 gm) on the first front arm at the motor end to get a good balance when you move clockwise looking from top. It's surprising that one rear side is real heavy :)
     
  20. exit 4

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    Ideally, if you had 4 scales like the one pictured, you could place one motor on each scale and see if any difference showed there. Then again, not many people have 4 scales? Unless you know people who are into that kind of stuff. Just a thought.