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Stress fractures... A theory

Discussion in 'Pro/Adv Discussion' started by Pepperami, Jul 7, 2015.

  1. Pepperami

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    Not that I know the definitive reason for stress fractures, but I do like to theorise :)

    As I've flown r/c heli's in my time one of the things that we all routinely did was blade balancing and there aren't that many threads on here regarding the practice

    The blades have to only be a little heavier on one side to cause them to put stress on the motors and housings, but in the P3 or indeed in any quad there are 4 of them

    This would not only cause more stressed on the components but an underlying vibration which could in the worst case scenario start to literally shake things loose

    How many of you actually balance your blades?
     
    skyhighdiver and clkilljoy like this.
  2. tvckz

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    I think 90% have no idea what you are talking about. We are solving 1.2.6 issue up here )))
     
  3. Oso

    Oso

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    My feedback (theory) in the other related threads has been the torque from the new motors and/or unbalanced props is stressing that area of the arm beyond its design limits. I personally don't think it has anything to do with over tightened screws. Even so, I don't do a good job of keeping my own props as balanced as I should. I've followed the several threads discussing balancing, but so far haven't really embraced it yet. I do intend to at some point soon.
     
  4. snerd

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    A couple of posters have said that most all of the DJI props are balanced very well from factory. I can only take their word, as I don't have a prop balancer. I sure would like to have one, though. I've been looking at the Du-Bro.
     
  5. Pepperami

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    Lol see that's what I thought.... I can almost hear people saying "blade balancing wtf is he talking about!" Lol

    I think it's worth considering, I know that there are lots of people unhappy with 1.2.6 and I get that for them it's a huge deal, others are more fortunate and have no problems with it and soon I hope DJI release a new Firmware to fix any issues

    I do think that blade balance is a key factor on any flying R/C model, the same as you balance the wheels on your car you can literally feel it through the steering when you have a badly balanced front wheel, and it's the same thing happening on a badly balanced blade!

    The over exaggerated example would be a plank of wood with 5kg on one tip and 5.5kg on the other and you spin it at several thousand RPM a minute.... We all know what's going to eventually happen, and yet such a simple thing goes mostly unrecognised let alone the subject actually approached and people doing it

    I'm sure the people on here that have flown R/C heli's will know what I mean :)
     
  6. BenDronePilot

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    I have the Du Bro as well as a dual sided threaded rod for the self tightening props. Works great
     
  7. snerd

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    How have you found the factory props? Balanced or off enough to make a difference?
     
  8. Pepperami

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    There's a guy in the UK making a really nice tool for the job and it's really quite reasonable in price and considering the costs of maybe another outer shell when they become available or the risk of screws falling out due the vibrations that are occurring I think it's worth the money

    I've not flown mine yet (still!) but I'll be getting one of these in the next week or so I think it's worth the investment
     
  9. Bluethundr

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    You know I thought this as well. But when I have had the bird in a hover at eye sight the tracking of the blades was perfect. I know back in the day of my gas helis you would have to add tape to one side of the rotor to get the correct 'balance" for the tracking. You could easily see if one side was heavier then the other.
     
  10. silverstoned83

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    Pitch corrects tracking, not balanced blades.
     
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  11. Pepperami

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    Yeah was going to put blade tracking is the tape on the blades but blade balancing is entirely different
     
  12. Dome

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    I second your idea.. just yesterday I felt slight different sound and controls from P3P and I shutted down all the stuff and take out P3A newer blades and tried on the P3P... it seems all normal and a bit different. Insect, dust, ground debris slashed during rotation, probably change the props balace a lot...
     
  13. Kman

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    I'll say this isn't a good theory.

    Almost all of the P3's with cracked shells is the inside screws on the rear arms. I think they are over tightening the screws at the factory.
     
  14. caffeinated

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    It's interesting actually. I've seen quite a few threads on here discussing causes, and possible prevention methods, for stress fractures but not a lot of threads complaining that they have stress fractures (in comparison to the other issues).

    I'm going to go hunting for them as I've missed them somewhere and my curiosity is piqued
     
  15. Pepperami

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    I'm glad to have evoked that curiosity :)

    Kman - yeah possibly, I'm not an expert and the screws being over tightened at the factory could be a cause for the fractures I agree, these are after all plastic shells, it's a shame they weren't carbon fibre with metal inserts for the screws..... No there's an idea :)
     
  16. 4wd

    4wd

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    Not my experience, I balanced them on day one and they needed a significant amount of work, very similar to the Vision Plus.. (no cracks here either!)
    Most won't be aware of vibration unless it affects the video - which the rubber balls and gimbal are very good at stopping.
     
  17. robinb

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    Mine were very close, took a very small amount of adjustment.
     
  18. BenDronePilot

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    I've gone through balancing around 10 props and some of them either did not need balancing it all or barely needed any adjustment. A few however needed more. Not too bad overall..

    I guess based on the 10 props I balanced you have roughly a 50 50 shot of it not really needing to be balanced as it's off by so little if at all. Maybe two of the props needed a little bit of time to get just right.

    Overall I wouldn't be too worried if you haven't been balancing your props. But if you're looking to eek out every bit of performance and increase the longevity of your rig it's still worth doing.
     
  19. clkilljoy

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    The P3 is so hard to take apart compared to the P2. I would take it apart and see if there is a gap under the screw in the shell and see if this is what is causing the cracking. If there is nothing underneath to support the shell to tighten up against it could be what is causing the cracks. I will remove the screws and see if there is a gap in the that location. ( I want to re-torque them all anyway) Good post. If it is not a design flaw, then something is causing it. Prop balance although slight is still one more thing to consider.
     
  20. Farmer

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    I recently purchased the threaded balancing rods for the Phantom range and a Dubro.
    Been working backwards through the P3 the P2 and now my P1.1.1, and concur with BenDronePilot, the Props are particulary well balanced and only a portion required adjustment.