Thera-Tube draw length

Discussion in 'General Slingshot Discussions' started by Juggle-Early, Dec 1, 2013.

  1. Juggle-Early

    Juggle-Early New Member

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    Hello. I have posted another thread about a project I am working on, but think I may have asked too many questions to generate responses. If you can answer this, or point me to where it has already been answered, I will be greatly appreciative. For my project I am looking to use 4 sections of either Thera-Tube Black or Silver. What I am trying to figure out is the draw length of these tubes. If I have 12 inches of tubing, how long will it be when stretched/drawn? Also, which if these colors will give me the greatest propulsion?
    Thank you for your assistance,
    Randy
     
  2. kohlqez

    kohlqez Accident-Prone

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    tt silver has a heavier draw which should translate to more propulsion, and for the draw length this is just a rough estimate as I sit here with about 12" of tts but I'd say it stretches to approximately 5 feet, but you will need extra to attach the bands. Also I'm not sure what your project is but four 12" pieces of TTS is a hell of a lot of draw weight for most project, you'd probably need a winch or something to draw it back
     

  3. Juggle-Early

    Juggle-Early New Member

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    Thanks for your reply. I posted my project in the New Idea section, titled Help!!! Basketball Slingshot. Here is what I am attempting:

    My contraption is just over 4 feet long. The tubes will attach at the rear of the main vertical section, up to the front posts (18 inches), around rollers, and then back a total of 27 inches. I will be connecting it to a rockwell Jaw Stand (pictured) so I can set the correct angle.

    It will have to travel a distance of 15 feet, with enough arc to go into a 10 foot high basket.

    Do you suggest something different? Should I consider stepping down to Black or Blue?
     
  4. 4foruglenncoco

    4foruglenncoco Member

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    I would buy the rubber that u would use more in the future for future projects
     
  5. Ghosth

    Ghosth Over the hill but still swinging!

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    Juggle most good quality rubber for slingshots will extend up to 500% of its original length.

    However the harder you work it, the more you stretch it the less time it will last. So 12" draw to 24" is 100% extension or quite conservative.

    What I have no idea of is if 4 pieces of Thera Tube black or silver is enough to loft a basketball? You may need all that draw length plus to get up that high, or you may only need half that.

    How much does a basketball weigh?
     
  6. kohlqez

    kohlqez Accident-Prone

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    I've never used it personally, but joerg has a calculator for draw length, projectile weight, etc. It might help or basketballs may be too big and heavy for it to work. How do you plan on drawing and releasing the rubber, maybe if you post a sketch I can be more helpful.
    Another idea would be to ask Joerg, as he is the master of all things rubber, but contacting him can be difficult...
     
  7. Juggle-Early

    Juggle-Early New Member

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    Thanks for the responses. I tried to contact Jeorg directly, with no luck, which is how I ended up here on the forum.

    A basketball weighs 22 oz., or 624 grams.

    Does the length of band increase or decrease the launch distance at all? Hypothetically speaking, would I get the same performance from a 1-foot section stretched to 500% as I would from a 3-foot section stretched to 500%?

    I have attached a picture of my PVC mock-up, which is going to be made from steel once I figure out how long I need to stretch the bands. I am planning to draw the bands back, and latch them into a gate hook, which will be activated by pulling a rope/string.
     

    Attached Files:

  8. Ghosth

    Ghosth Over the hill but still swinging!

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    The only way I see to solve this is to do some testing. Try 4 12" pieces of tubing either black or silver and see if it will launch a basketball at 24" draw. What you learn there should help you discover the answers. I don't have enough rubber in anything but Thera band Red and no basketball so I'm no help.

    I see your PVC mockup but I don't understand how you think it is going to work. Much less 4 likely points to attach tubes at. It seems overcomplicated, but then I probably don't totally understand what your trying to do.
    I see 4 sets of "legs" across the bottom on something that probably doesn't need "legs" at all. Or I'm totally misreading what all those parts are supposed to do.

    I would think you would want 4 full length "rails" to cage the basketball, to control its direction. So in effect they become the barrel of the basketball "cannon". Tubes attach to the far end of the frame holding those rails to give you your motive power. You will probably want something like a 4 cornered net "pouch" to hold the ammo. You can probably use para-cord from each tube -pouch attach point to create a way to lock it in loaded position. From that point figuring out a trigger release should be easy.

    I admire what you are trying to do, best of luck with it!



    Slingshotters shoot 8-12mm balls for the most part, normally weighing from 1/4 to 1/2 an ounce. So your talking several orders of magnitude stronger. But, you probably only need 15' of total height, and perhaps 30-40 feet distance.

    Yes, drawing back farther adds speed/force. But for the most part we do not launch things as heavy as basketballs.
     
  9. Juggle-Early

    Juggle-Early New Member

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    Here is an updated picture. I have used jump ropes to represent the theraband as a reference point. I am planning to use a smaller ring as the "pouch" for the ball to rest in. The silver duct tape band in the picture will hook into a gate latch at the rear, which will be released by pulling on a rope. I hope this helps to clarify some design questions.
     

    Attached Files:

  10. Ghosth

    Ghosth Over the hill but still swinging!

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    Actually that makes a world of difference!

    Ring and strap on basketball looks fine. Should be easy to setup a trigger.

    So it comes down to the point where you tie on 4 tubes and see if the basketball fly's, and how far, how high.
     
  11. Juggle-Early

    Juggle-Early New Member

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    So I had quite an interresting brainstorming session with one of the Physics teachers from my school yesterday. What we found was that, theorhetically speaking, my idea of 4 bands of Silver would shoot the ball over 300 feet, and would require a wench to draw it back. We worked it through, adjusting launch angle and band strengths, and have settled on TheraBand Green Tubing. I placed my order yesterday. Now, off to the metal fabricator. Once everything is done, I will be sure to post pictures and videos.
    Thanks,
    Randy
     
  12. Ghosth

    Ghosth Over the hill but still swinging!

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