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Strong, flexible material

  1. Sep 2, 2016 #1
    I recently built a backpack system for carrying a camera stabilizer. I have two rods that come up out of the backpack and over the shoulders. Wire is attached to the end of the rods, and the camera is hung from the wires. The rods are run up straight out the backpack, but the weight of the camera bends them over the shoulders into position. The camera is under 15 pounds.
    I built it with fiberglass rods which worked great, but after a couple of weeks of use, the rods cracked, then broke.
    Is there a material that would be flexible enough to bend over the shoulders, yet strong enough to hold 15 pounds on a regular basis?
     

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  3. Sep 2, 2016 #2

    CWatters

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    You could try Kevlar or Carbon rods but at some cost. I think I would experiment with different diameter fibreglass rods.

    Where did the rods fail? Did they fail in the middle or at a stress point where they connect to the pack or camera?

    The camera might only weigh 15lbs but is the rig actually carrying the weight of your arms once they become too tired to hold the camera up?
     
  4. Sep 2, 2016 #3
    Nitinol?
     
  5. Sep 2, 2016 #4

    anorlunda

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    I think fiberglass is a good material. Maybe you can tweak the parameters.

    If the rods were longer, the bending radius would be greater.
    Slightly larger diameter rods would be stronger.
    Cross woven fiberglass cloth molded into the rods influence strength and durability.
    Perhaps a wire rope core to the glass rod.

    You need a fiberglass consultant, or a book.
     
  6. Sep 2, 2016 #5

    Baluncore

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    You need to switch from glass fibre filled with polyester resin to either Kevlar or carbon fibre filled with epoxy resin. Polyester resin does not chemically bond to the glass fibres. Epoxy bonds well to Kevlar.
    There are flexible epoxy resins available that are more reliable than brittle polyester and glass.
     
  7. Sep 3, 2016 #6

    Nidum

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    Special grades of carbon fibre and glass fibre are available for making fishing rods .
     
  8. Sep 3, 2016 #7

    anorlunda

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    Yes, good one @Nidum for stating the obvious. Buy fishing rods and adapt them to your use. They are already optimized for that bending duty and they come in many sizes and strengths.
     
  9. Sep 3, 2016 #8
  10. Sep 3, 2016 #9

    Vanadium 50

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    Have you considered tubes instead of rods?
     
  11. Sep 3, 2016 #10

    Baluncore

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    A tube is used where rigidity is wanted. In this case a springy structure is needed. A tube may collapse and so will be more fragile than a solid rod or a laminated flat section.

    A rectangular section strip bending through 90° can twist and so may flex sideways as well as up and down. Consider wide flat sail battens from a ship chandlers, avoid the rigid foam sandwich. You might slightly taper the batten in width so as to flex in a convenient position.

    Another solution may be to cut an archery longbow in two. Use two short rigid tubes in the pack to extend the cut ends, with the flexible tips bending forward over the shoulders to support the camera.
     
  12. Sep 4, 2016 #11
    Thank you so much for all the replies, I will look into all the options you guys have presented. The fiberglass rods I used were 9mm in diameter and hollow. I had steel wire running through the middle for safety. I was using two 1.5' sections joined by a coupler in the middle for portability. That is where they failed, right after the coupler.
     
  13. Sep 4, 2016 #12

    Vanadium 50

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    By volume. By weight a tube is stronger. In any event, it gives you one additional degree of freedom to work with.
     
  14. Sep 4, 2016 #13
    You could try fiberglass tenth poles. They're very strong and inexpensive, and you can choose different diameter and stiffness, or just couple two of them if your camera is too heavy
     
  15. Sep 4, 2016 #14

    Baluncore

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    I presume by “stronger” you mean more rigid. But the OP wants more reliable “soft” springs that droop forward over the shoulder.

    The first thing that extra degree of freedom allows is to eliminate cavities in the spring, at the same time eliminating that extra degree of freedom. The one thing avoided in soft springs is an open cavity that might collapse. Ask yourself why coil springs are made from solid wire or rod, and why leaf springs are made from flat strips, often laminated.

    When hanging a mass so it will “spring back” to point the same way, consider a tube, a rod or a flat tape. For the same mass and tensile strength, a torque tube will be most rigid, a solid round rod comes next, followed by a flat strip or tape that will be the least rigid and so most free.

    If the OP used a flat strip, then it could bend forward to support the mass, yet be more free to rotate. That would eliminate more left–right sideways motion when walking.
     
  16. Sep 5, 2016 #15

    CWatters

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    Sounds like the cause of the problem was stress concentration. Perhaps caused by the coupler being too rigid compared to the rod or by the end of the wire inside?
     
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