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  1. #1
    CPM M4 BananaTugger's Avatar
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    What kind of wood should I use to make a catapult?

    I have to make a catapult for my Principals of Engineering class, and we have to pick our own materials and construction methods.

    I was thinking of something kindy heavy, like Cedar, but if might be to hard to work with.

    What about Balsa? It's light and stiff, but I don't know how strong it is, and I'm afraid it might crack at the pivot points.

    Where should I use glue? Does would glue work just fine or should I get that Gorrilla stuff?

    Rosewood? That stuff is expensive, but it's strong. So is Cherry.

    Plywood? Or is that too pedestrian? I am a Weight Weenie/OCP'er you know.

    The catapult has to be powered by a spring, and is about three feet tall.

    Thanks.

  2. #2
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    Are you allowed to build a trebuchet? The wood you use is far less important than the design (i.e., pine would be fine).

  3. #3
    CPM M4 BananaTugger's Avatar
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    Quote Originally Posted by erraticrider
    Are you allowed to build a trebuchet? The wood you use is far less important than the design (i.e., pine would be fine).
    No, that's the next thing we're going to build, for now it's a spring powered job.

  4. #4
    Hazardous Taerom's Avatar
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    How big is it going to be? I'd say just go with some pine lumber. Cheap, strong, looks good...

  5. #5
    CPM M4 BananaTugger's Avatar
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    Quote Originally Posted by Taerom
    How big is it going to be? I'd say just go with some pine lumber. Cheap, strong, looks good...
    Three feet tall, minimum.

    Width and length are up to me.

    Pine... sounds good. I'll find a sample at the local 84 and see if it is suitable.

  6. #6
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    Oak is what traditionally used for the base, and spruce and fir were used for throwing arms.
    Balsa has very little compressive strength, you can crush it in your hand, it's also expensive.
    Poplar would work, it has less sap, a finer grain, and is a little easier to work with than pine.
    A sanded ply would also be something to consider. It's strong, large, and can be relatively light. I would not recommend it for throwing arms though.

    Yellow wood glue or Gorilla glue will work. In either case glue joints should be clamped or screwed together.

    Luck,
    --A

  7. #7
    It is what it is... Minesbroken's Avatar
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    you need a material that bends without snapping...stay away from hardwoods....balsa is brittle and would just break probably.
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  8. #8
    Senior Member
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    Quote Originally Posted by BananaTugger
    No, that's the next thing we're going to build, for now it's a spring powered job.

    a trebuchet can be powered by a spring -- i.e., one where the spring tension comes from being stretched, rather than compressed.

  9. #9
    Non Tribuo Anus Rodentum and off to the next adventure (RIP) Stacey's Avatar
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    notrem, Notrem, NOTREM!!!

  10. #10
    It is what it is... Minesbroken's Avatar
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    notrem?
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  11. #11
    Non Tribuo Anus Rodentum and off to the next adventure (RIP) Stacey's Avatar
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    Think: "The Shining"

  12. #12
    It is what it is... Minesbroken's Avatar
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    Lol
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  13. #13
    2-Cyl, 1/2 HP @ 90 RPM slvoid's Avatar
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    Ideally, you'd want something with huge elastic modulus. I recommend carbon fiber.

  14. #14
    explody pup
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    Quote Originally Posted by slvoid
    Ideally, you'd want something with huge elastic modulus. I recommend carbon fiber.
    I was going to suggest CF wrapped around/bonded to balsa wood.

  15. #15
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    Quote Originally Posted by slvoid
    Ideally, you'd want something with huge elastic modulus. I recommend carbon fiber.

    only if you are using the wood to create the spring tension.

  16. #16
    It is what it is... Minesbroken's Avatar
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    yeah, wouldnt it be the rope that creates the tension on a catapult?
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  17. #17
    Third World Layabout crtreedude's Avatar
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    How much weight do you plan on flinging? That is your criteria. My I not so humbly suggest ash? After all, it is what bats are often made of. You want a bit of rigidity that will spring back. Ash is also generally very straight grain. Hickory would probably do well as well - used a lot for handles on tools.

    Want exotic? I think Mango would be something that would work well - it is used for ox yokes down here - pretty light, but very tough. If weight is no issue, I can suggest things that are one step away from steel.

    Balsa down here is nearly free - 1 year from seedling is a 12" diameter tree. Not kidding. I wouldn't think of using it, it would collapse most likely. It is pretty tough though for such a soft wood.

    You also might do some research into woods suitable for bows (as in archery) - the most famous is Osage Orange and for a long bow, Yew. Down here we have something called Peyibeja (I think I spelled it right) which almost looks like a palm, the original people here used it for making bows - incredible stuff. This will allow your spring to load the wood - not sure that is your goal. If rigidity is the key - then I might go with iron woods - check out Ipe (for something you should be able to get) - VERY hard, very rigid.

    But I really don't think you could go wrong with ash - and it should be readily available. Also, hard maple (most dowels you buy will be of this) is a good choice as well.

  18. #18
    Third World Layabout crtreedude's Avatar
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    Oh, I don't recommend a banana trees - won't work for sure.

  19. #19
    Hey guyz? Guyz? Wait up!! Siu Blue Wind's Avatar
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    Quote Originally Posted by Stacey
    notrem, Notrem, NOTREM!!!

    Wannabe Notrem. Never. Nobody else can ever be.
    Quote Originally Posted by Buddha
    We are what we think. All that we are arises with our thoughts. With our thoughts, we make the world.
    Quote Originally Posted by making View Post
    Please dont outsmart the censor. That is a very expensive censor and every time one of you guys outsmart it it makes someone at the home office feel bad. We dont wanna do that. So dont cleverly disguise bad words.

  20. #20
    explody pup
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    Quote Originally Posted by crtreedude
    Oh, I don't recommend a banana trees - won't work for sure.
    And I was just about to recommend banana trees!

  21. #21
    Senior Member
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    Quote Originally Posted by crtreedude
    Oh, I don't recommend a banana trees - won't work for sure.

    There are other similar "woods" that I would not recommend.

  22. #22
    Non Tribuo Anus Rodentum and off to the next adventure (RIP) Stacey's Avatar
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    I wanna see you fling a piano with THAT wood!

  23. #23
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    Quote Originally Posted by Stacey
    I wanna see you fling a piano with THAT wood!

    Only people who are very special to me get to see that.

  24. #24
    It is what it is... Minesbroken's Avatar
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    Morning wood? *sits with eyes closed waiting for the abuse to start*
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  25. #25
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    Quote Originally Posted by Stacey
    notrem, Notrem, NOTREM!!!
    exactly what I thought when I saw this thread!
    but noone could really copie him

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