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Thread: 8 inch props?

  1. #1
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    8 inch props?

    Hi guys,

    Ive got a dji 550, it comes with 8" props and 10" props in the box. The instructions say 8" for 4 cell lipos and 10" for three cells. I have three cell lipos but ran the hexa on 8" props before figuring out the instructions. Since switching tomthe 10" it handles like crap! Way to twitchy nomatter what i set gains and stick scaling to. Question is am i just crap at flying and this is the way the hexa handles with a kk2 or can i fly it on the 8" props and not hurt the motors and batteries?

    Sorry if a silly question,

    Mountie

  2. #2
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    I bet those motors are getting mighty hot trying to spin fast enough to keep that hex in the air on 3S packs... Handling is due to tuning. If you're running a KK2 there are countless tuning guides online so I suggest looking into that. Were you using the stock PID's w/ 10" props?
    -Chris
    www.youtube.com/user/criccio

    [QUOTE=Zeeflyboy;562833]If it all ends badly this time, I'm quitting FPV and RC and taking up golf.[/QUOTE]

  3. #3
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    Stock pid? Sorry total beginer here.

    8s handles better 10s had way more torque but i couldnt get the hang of them.

  4. #4
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    Quote Originally Posted by Mountie View Post
    Stock pid? Sorry total beginer here.

    8s handles better 10s had way more torque but i couldnt get the hang of them.
    No, you're not going nuts and the problem is not tuning.

    I'll give you the solution first, then the explanation. Get a set of APC 8x4.5MR's _and_ a couple sets of the spacers, you'll probably have to order them direct from APC at apcprop.com, since it's hard to find them in stock in most places. Do NOT use the DJI 8" props at all and avoid the 10" props (or cut them down as I suggest below).

    Now the explanation: The 10" DJI props are too heavy; they're durable and give good lift, but they also give a spongy, bouncy response which will drive you insane while FPV. It's slightly better in manual mode and with the attitude gains turned way way down, but it's still going to make you seasick, especially in a stiff wind. The 8" props do throw blades! Especially on 4S; they're just too weak to take the punishment of those rpms and get into a flutter situation very easily. The blade chucking in flight is bad and will lead to a crash (I've thrown 2 blades with these on my f550).

    So ditch all those props and go with the APC's. They completely fix the problem and restore it to flying like a jet like it's supposed to .
    PS: in the meanwhile, you can trim the 10" props down to 9". This won't stop the spongyness, but it'll help somewhat. That way you can at least have something to fly until you get your APC's in...

    LS
    Last edited by lucien; 6th November 2013 at 10:59 PM.

  5. #5
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    Thank you very much for the insight, one question is there only one apc to choose from all the same pitch?

  6. #6
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    Quote Originally Posted by Mountie View Post
    Thank you very much for the insight, one question is there only one apc to choose from all the same pitch?
    I'm not 100% sure what you mean, but an 8x4.5 is what seems to be called out for when flying on 4S. And it so happens that APC makes a multirotor prop in exactly that size. But they have other sizes:

    http://www.apcprop.com/SearchResults.asp?Cat=28

    you of course need 3 of each, 3 regular and 3 "pushers". And you'll need the plastic inserts also to get the correct fit onto the motor shafts (as well as a taper reamer to ream out the holes).

    But the 8" is really what you want for FPV on the f550, since they give a completely bounce-free, super sharp response in flight. Larger props may work but the additional weight (moment of inertia) may introduce the bouncy-bouncies again....

    PS: I should add that the bouncies tend to not be as bad if you're carrying a lot of weight on the aircraft. My f550 is totally bare, just the batts and FPV equipment. No landing gear, no GoPro, no nothing. So the bigger props really make mine wobbly. But if you're more loaded up, 9" or 10" props will work better... So yeah you may have to experiment some in that case. Also, you can fly the 8" props on 3S, but the performance will be pretty marginal. No, it won't cook the motors/ESC's. But, the throttle stick will be near 3/4 full for most of the flight and towards the end of the pack you'll be nearly at full throttle in the hover. I recommend 4S with the 8" props, since you'll need the RPM's...

    LS
    Last edited by lucien; 7th November 2013 at 09:31 AM.

  7. #7
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    Makes good sense to me thank you

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