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Dual battery mount (sides) - Experiences?

Discussion in 'General Discussion' started by Howzit, Mar 29, 2014.

  1. Howzit

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    I know there have been some issues when running the dual battery mounts that hang the batteries off the sides, but I'd like to get an idea of what sort of problems you had and what you were doing when the problem occurred. Is the issue during descent only, or does it cause random instability? I'd like to push my FPV out a bit further, and an extra 2 mins would get me to my goal.

    If its just the descent that has been causing the issues, I can manage that.

    FYI, this is the mount I am speaking of:

    [​IMG]
     
  2. OI Photography

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    I had those exact mount and used them for a while before ditching them. It seemed that no matter what battery I put on them (even the stock DJI 2200's), there was noticeably less stability across the board. Can't say if that was all due to aerodynamic effect or just because of the change in weight distribution, but I'm happier without them.

    The locations they're at can affect the downwash from the props and cut into the total amount of lift produced as well, which logically would also cause the vortex ring state to take effect sooner on descent.
     
  3. Howzit

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    Did you ever go with a different dual mount setup. Perhaps d3wey's?
     
  4. OI Photography

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    Sure did (D3wey's), and as long as you're not loaded too heavy overall it works great! I used the original P1 "FPV Undertray" he makes (non-Zenmuse version). What video transmitter are you using? Both the fatshark 250mW and the Immersion 600mW will fit in the mount on it, the latter will just take some minor trimming...not sure about other brands.
     
  5. Howzit

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    I'm using the fatshark 250mw, so all should be well.

    Where did you pick up the 4 little metal extensions that are needed for the under tray? I assume any local hardware store should carry such things? Also, I assume stability was improved? Any recording of improved times with stock batteries or mad dogs? I'd guess in the 2-3 minute range?
     
  6. OI Photography

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    If your total flying weight (AUW) is 1300g or less, then adding a 2nd batt of the same capacity should net you ~50% increase in flight time over a single batt of that capacity, and my real-world use did exactly that or just a smidgen better.

    Hanging the 2nd batt under the middle of the body also lowers the COG, contributing to better balance on the aircraft.

    The 25mm brass extensions for D3wey's undertray were hard for me to find domestically, I had to order a set of 25 from China. If you're in the US and need some just let me know, I'll be happy to drop a few in the mail for you.
     
  7. DeweyAXD

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    The NAZA seems very unhappy about weight being added outside its centre axis. Due to the Phantoms smallish 330mm frame size the winglets seem to cause the NAZA to get in a real muddle if you over cook the descent and let it roll over too far. The result (as a fair few have experianced) is almost total loss of vertical control. It is recoverable if high enough up (and with enough left in the batts) but if not it can end in a very hard and heavy landing. Seems to be known as the 'Death Wobble' (example here: http://www.djiguys.com/Forum/viewtopic.php?f=4&t=3629) and every time I see someone post about it they seem to have this setup. They also seem to get a little in the prop wash (one guy suffered the wobble with them attached but with not batts on them!).

    Don't get me wrong my FPV undertray design won't mean you can go doing flips and rolls but the lowered CG as OI mentioned does seem to make the NAZA cope much better on descents and heavy pitching or rolling as when you come off the sticks gravity helps to swing the body back level and the NAZA does the rest.
    While I can't really prove it I also feel that the less compensation the NAZA has to do in GPS mode, the less power is used.
     
  8. ElGuano

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    350mm :). We're not running f330s here!
     
  9. Gizmo3000

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    I've no experience, but it seems that of the people I know who've tried it, many are dissatisfied with the results.
    not only is the craft unusually heavy and less nimble, but the wings catch some of the prop wash apparently.

    My advice to those who want longer flight times
    - get larger 9" Vision style props
    - try a 2800mah battery instead of duals
    - lighten your Phantom if any way possible (don't bother with landing gear extensions for instance)
    -cautiously lower your Battery Failsafe levels a bit

    and then just be happy and learn to fly and shoot with whatever flight time you end up with.

    still not happy? then
    - get a P2
    - build a quad that accepts larger batteries. (I would get about 11 minutes with my F450 with 4500mah batteries)
     
  10. Howzit

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    OI Photography,

    PM sent.