Booms Twisting

Discussion in 'Cinestar 8' started by Tristan Twisselman, Feb 19, 2015.

  1. Tristan Twisselman

    Tristan Twisselman Active Member

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    So I am starting to think my last crash may have had something to do with the boom twisting mid flight. Although I have had them twist in the past and not cause a crash the copter definitely doesn't react or fly as smoothly when they are twisted. I have metal boom clamps and they are as tight as they can possibly get without stripping or snapping the bolt. I even lightly scuffed/sanded where they mount. The only other thing I can think of at this point is to drill a small hole and use a set screw to keep the booms from rotating. I do this on the tail boom of all my 3D helis to keep it from rotating...thoughts?
     
  2. Steve Maller

    Steve Maller UAV Grief Counselor

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    I have definitely had this happen to me, but I don't think you are going down the right path thinking about drilling holes in the carbon fiber arms. The metal boom clamps and carbon fiber arms should work really well. However, if you are using cheap aftermarket parts, there is a good chance that you don't have a good fit, or the materials are substandard. I'm not making accusations here, just trying to help you figure out what happened. I would not drill holes in carbon fiber arms, as that can substantially weaken them, and have a negative effect on their stability.

    What kind of evidence did you see that gives you the thought that a twisting arm would have led to your problem? I've had two situations arise where that definitely happened, and in one of them I actually had some camera footage which supported that. Fortunately, in both cases I was able to recover and get the copter on the ground in one piece.
     
  3. Tristan Twisselman

    Tristan Twisselman Active Member

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    Hey Steve,

    I'm using FreeFly everything. Frame, booms, boom clamps, heavy lifter motor mounts or whatever they are called they sell. It's all FreeFly/cinestar stuff. I don't know what else to do at this point
     
  4. Gary Haynes

    Gary Haynes Administrator
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    Or the motor mounts rotated? Metal clamps on the motor mounts?
     
  5. Tristan Twisselman

    Tristan Twisselman Active Member

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    Metal clamps all around.
     
  6. Gary Haynes

    Gary Haynes Administrator
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    Consider putting alignment marks using a metallic ink pen on the boom/center section junction and same on the motor/boom end so that you can see if you are getting any rotation. I haven't seen any rotation of a boom. And unless there has been a delimitation/failure on the boom structurally by their nature I would be surprised if we have enough torsion to 'twist' the actual boom tube itself. Andy might have an opinion on that.

    I don't do this anymore but early on I always used Loctite 222 on the bolt threads.
     
  7. Steve Maller

    Steve Maller UAV Grief Counselor

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    In my experience, metal boom clamps CAN twist, but only if the screws become loose. So as part of my preflight I do typically go through all of the screws to make sure nothing has come loose. But if they are sufficiently torqued, they should not slip.

    Did you experience and uncontrollable spin with your copter? In my experience that is the symptom of a loose boom.
     
  8. Dave King

    Dave King Well-Known Member

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  9. Steve Maller

    Steve Maller UAV Grief Counselor

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  10. Dave King

    Dave King Well-Known Member

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    HI Steve

    No I haven't had any need to try them with the flat 8 combo. I have absolutely no movement what so ever on my booms. I couldn't move them if my life depended on it. Johnny Beaver posted them on facebook and he has tried them on his big rigs with the big KDE motors and has not had any issues.

    I liked the idea so that motor alignment wouldn't be a problem provided the clamp was tightened down evenly.
     
  11. Ryan McMaster

    Ryan McMaster Active Member

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    They will be a bit weaker due to the flat part on the boom. A cylinder is always much stronger. The one concern I would have with them is a rough landing would induce quite a bit more flex that could cause a break where a cylinder does not. The crush resistance on these booms will be much lower compared to a cylinder too.
     
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  12. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Cylindrical booms do have the advantage that, if you have a crash, they absorb some of the kinetic energy by allowing things clamped to the boom to rotate.... The downside with the metal boom clamps is that they bite down so hard that that rotation doesn't happen so I have a suspicion that you will see more booms breaking. Just a theory...

    Andy.
     
  13. Dave King

    Dave King Well-Known Member

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    Everything has its advantages and disadvantages. Sometimes you need to use certain things out of necessity. If the booms are rotating this is the perfect way to prevent that from happening which will PREVENT CRASHES. Johnny Beaver wouldn't use them on his Heavy lift rigs if they didn't work. If you don't know who he is he's one of the most serious drone guys out there with many years of experience. I also know Howard Depp uses a similar design although he doesn't use the ones from this company.
     
  14. Howard Dapp

    Howard Dapp Active Member

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    I've been using square and flat surface/rounded cornered booms for 5 years after 3 years of round tube. One thing I can say is I've never experienced an uncontrolled situation due to boom rotation...just one less potential issue to look out for during preflight check. This is one of the reasons why I went this route. Hobby grade thin walled round boom tube, in my opinion, is no stronger than what I am using for booms. At the weights most of us here are flying, in combination with larger more powerful motors, I believe that currently available boom clamps need more clamping surface area...increase the width x2 or 3.

    This topic just reminded me that I need to fnd a solution for my handheld gimbal...when I go inverted I'm experiencing boom rotation at the pan boom when kitted with an Epic. Yes, all metal clamps tightened to its limit.
     
  15. Steve Maller

    Steve Maller UAV Grief Counselor

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    Sagely advice, Dave!

    Howard, whose booms & clamps are you using?
     
  16. Ozkan Erden

    Ozkan Erden Distributor

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    I have changed my carbon booms with 2mm wall thickness versions. Stock Cinestar boom's have 1mm wall thickness which is not strong and it will crack if you overtight with aluminum clamps. After upgrading the booms, I can tight the clamps more without worrying about cracking them and also, the frame becomes much more rigid, there isn't any resonance any more with big motors and heavy payloads.

    Btw, I am using custom aluminum clamps they are not original Freefly clamps.
     
  17. Ryan McMaster

    Ryan McMaster Active Member

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    Where are you getting your 2mm from Ozkan? Are you buying it as stock?
     
  18. Ryan McMaster

    Ryan McMaster Active Member

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    They are good booms.

    The material science behind using a tube vs a flat round in this application is what prompted my comment. The stress induction from landing/takeoff/general flying and the higher rate of flex in a flat round vs a cylindrical boom in a heavy lift MR application is a concern. The flat round tube over time will develop stress cracks along the longitudinal axis (top and sides), that may or may not be visible due to the way carbon fiber tube is made, which could cause a serious crash if it decides to break mid flight or shear and the clamps no longer have purchase on them. Motor vibration will amplify this effect, especially in heavy lift rigs and rigs with weak center hub mounting.

    Yes, a Round tube can rotate, but that gives a confirmed visual on pre-flight that can be rectified in the field at no cost and minimal time. I know for a fact the stock Cinestar 500mm boom can take close to 150lbs of direct force before they buckle (partial tube collapse, note still flyable for an emergency landing), and it takes around 215lbs to crack and fracture (total tube failure) the carbon.

    The aluminum clamps combined with Ozkan's suggestion of booms with 2mm walls would be the way to go. The use of a clamp with more purchace and (Grips more of the boom) would also reduce stress related failures in either boom setup.
     
  19. Ozkan Erden

    Ozkan Erden Distributor

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    I found a local supplier; they sell in 100cm lenght. (I'm located in Turkey btw). I cut them.

    I remember searching it on Ebay and came up with plenty of results:

    http://www.ebay.com/itm/25mm-X-21mm...449?pt=LH_DefaultDomain_0&hash=item1c4e65eef9

    It adds some weight to the overall frame weight but I regret not doing it before.
     
  20. Howard Dapp

    Howard Dapp Active Member

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    We've been using aluminum for many years, no threat of invisible cracks. We do a lot of traveling with our equipment and find ourselves in challenging shooting location where, from OUR experience, cf booms just wouldn't hold up, frayed edges,constantly checking for motor level etc. We just returned from a shoot in the the Middle East where we had to chase offroad vehicles over rough terrain while trying to secure our fully built up copters in the back of an SUV...Aluminum is more forgiving when being bump around into other objects...CF booms just aren't rugged enough for us.

    Our arms slide into square aluminum sleeves, no need to check for motor level, which makes break down and setup extremely quick when arriving on set (we like traveling as compact as possible). I think CF tube wear down/compress some around the clamp area when loosened and tightened repeatedly, not sure but I believe we're experiencing this on one of our gimbals...this could be why some experience boom rotation over time

    We're happy with our setup.
     

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