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  1. #1
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    Aluminum Spreader Bar & Strength

    Has anyone try using 0.6" dia aluminum tubing as spreader bar? does curve spreader bar preventing the hammock from flipping over? would the tubing has more strength with more sections or less sections? if i were to bend the aluminum tubing, would the pulling force on the hammock bend the tubing even more?

    Thanks guys!!

    Below is my first prototype on the redesign of hammock tent.
    i want to figure out some of the engineer and weight aspect before I move forward with the design. Thanks!

    Last edited by Henrykhwu; 04-07-2013 at 22:55.

  2. #2
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    I do not know about the spreader bars, but that is a neat idea for the poles to create it into a "tent", without being claustrophobic.

    Are you using tent poles that can collapse down?

  3. #3
    Jazilla's Avatar
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    Neat idea. Is the top made of water proof material?
    Yosemite Sam: Are you trying to make me look a fool?
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  4. #4
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    Quote Originally Posted by lubbockhammockguy View Post
    I do not know about the spreader bars, but that is a neat idea for the poles to create it into a "tent", without being claustrophobic.

    Are you using tent poles that can collapse down?
    yes, I am. it will be collapsable so you can assemble it. and Thanks!

  5. #5
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    Quote Originally Posted by Jazilla View Post
    Neat idea. Is the top made of water proof material?
    That is made out of ripstop nylon.

  6. #6
    Jazilla's Avatar
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    Really cool idea. The cover being made of ripstop will hold some warmth in the winter, may even cause condensation if it isn't vented. During the spring and summer its going to be mighty warm in there. What's the intended purpose of the nylon cover?
    Yosemite Sam: Are you trying to make me look a fool?
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  7. #7
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    From the picture of your hammock it appears there are significant bending stresses applied to the wood spreader bars you are using. You are attaching the ends of the hammock to the spreader bars at two locations a distance away from where the suspension triangle is attached. The distance between these points multiplied by the force applied to the bar by the hammock body results in a bending moment. Additionally, you have a compressive force applied to the end of the spreader bars by the suspension triangle. Assuming the end suspension is carrying a tensile force equal to the weight of the occupant, the compressive force on the bar will be:

    1/2 * w * cos(angle)

    where the angle is measured between the spreader bar and one of the sides of the suspension triangle.

    If you can calculate how much moment is being applied to the bar, and you know the compressive forces, you can calculate what diameter and tube thickness are needed to resist those forces. If you use a segmented bar, the moment in the bar at the joint will need to be calculated and checked against the resistive capacity of the connection.

    Don't forget to include a significant factor of safety due to additional dynamic forces of getting in & out of the hammock, etc.

    If you use curved bars, things get more complicated. The curve in the bar applies more moment to the spreader due to the compressive force acting on the ends. This moment starts out as the compressive force on the bar multiplied by the distance from the middle of the bar to its straight-line position if you didn't use a curved bar. Deflections caused by this moment, and the applied moment from the hammock also cause an additional moment to be applied to the bar. This "P-delta" effect is usually calculated iteratively until the subsequent calculated deflections are small enough to be a rounding error.

    If the bar is too small, the deflections from the starting position will continue to failure.

    So, there is a way to calculate all this, but it is a bit obtuse, and your best bet is find an engineering friend who has taken mechanics of materials and statics. They can help you calculate it out.

    Otherwise, start beefy and go from there. Based on the extra moments you are putting on this bar, you need to start with something much heavier than the straight spreader bars you would see on other bridge hammocks in the forums.

    Quite an interesting clamshell design you have there. Looks pretty neat.

    Good luck.

  8. #8
    Senior Member Labrador's Avatar
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    That looks really cool. A waterproof breathable material would be really cool as a cover.

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