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Thread: Catapult!

  1. #1
    Rails against Big Carrot JohnnyEgo's Avatar
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    Default Catapult!

    My son is in 5th grade, which means it's science fair time in this county. After ruling out all the ideas that were improbable if not impossible, such as the robot butler and the hoverboard, and the things I was not willing to do, like the paper mache volcano or winding 40 feet of copper around a motor armeture, we stumbled across ballistic trajectory as a topic. Which totally called for catapults.
    Had my son draw up a design first:

    Then grab some scrap out of the bins:


    He crosscut the maple base and frame arms with the sled.



    Then he cut the finger joints on sled jr.


    I did the single rip cut because it was fairly narrow, then he took over with the walnut for the multi-angle base.
    Math is tough. Let's go shopping!

  2. #2
    Rails against Big Carrot JohnnyEgo's Avatar
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    Drilled holes in the frame for the pivot arm.


    Drilled holes for the angled base.


    I trimmed up the lever arm on the bandsaw. I won't let him anywhere near the router, so I also knocked the edges off with a roundover bit. Then back to him for glue and clamps.




    Two wiped on coats of Danish oil for the win.





    We originally used 4 rubber bands, which ended up launching the ping pong balls something like 20 feet. I down-powered it so we could run the experiments at a reasonable scale in the garage.


    We used video to determine the horizontal distance and elapsed time. In the context of his algebra-less experiment, that was enough to prove which launch angle sent the ball the furthest. I showed him how to use the kinematic equations to resolve vertical displacement and the component vectors of velocity, but I wouldn't say he was highly interested in that. But we had fun making the catapult and shooting ping pong balls all over the place. And when Mom wasn't looking, we launched cherry tomatoes all over the kitchen as well.

    I am proud of the fact that his project represents both his actual levels of understanding and effort, and I look forward to seeing it between the projects of the kids who home-sequenced the genome of their dog and the one who built a functional model of the Jarvik heart.
    Math is tough. Let's go shopping!

  3. #3
    Prefers it FIRM Skully's Avatar
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    That friggin cool!

    Now, on to a full size one for the front yard and capable of launching farm animals.................
    "The rifle itself has no moral stature, since it has no will of its own. Naturally, it may be used by evil men for evil purposes, but there are more good men than evil, and while the latter cannot be persuaded to the path of righteousness by propaganda, they can certainly be corrected by good men with rifles. --Jeff Cooper"



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  4. #4
    QUITTER Irving's Avatar
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    I didn't make a catapult until 11th grade physics. A few years ago we picked a science fair project that got the school district, and the state involved, and all the other group member parents bailed their kids out of the project. Nicely done.

  5. #5
    Zombie Slayer MrPrena's Avatar
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    That is 1st prize for sure!

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    Gong Shooter copfish's Avatar
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    Awesome project! Looks good too! Let us know how it was received.
    I shoot, therefore I am. Vivere die!

  7. #7
    Rails against Big Carrot JohnnyEgo's Avatar
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    Quote Originally Posted by Irving View Post
    I didn't make a catapult until 11th grade physics. A few years ago we picked a science fair project that got the school district, and the state involved, and all the other group member parents bailed their kids out of the project. Nicely done.
    That must have been a hell of a project!
    Math is tough. Let's go shopping!

  8. #8
    Paper Hunter To Bear Arms's Avatar
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    Dang! Not sound gay or anything, But I always enjoying looking at pictures of your wood projects!! And I thought it would be bigger! But that is a sweet catapult! Glad to see your Son using the power tools and hope he enjoys his time with his Dad in the shop.
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    The "Godfather" of COAR Great-Kazoo's Avatar
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    He is definitely getting taller. Soon he'll be showing you how to make those projects
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  10. #10
    Rails against Big Carrot JohnnyEgo's Avatar
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    Haha I think I could scale it rather easily out of a piece of plywood and some bungees, but we get into enough trouble with the neighbors as it is.

    I'd like to believe he will look back on this and enjoy it. Mostly, he considered it a needless distraction that took him away from his video game for an entire Saturday. I've been trying to reinforce the concept of finding satisfaction in the completion of a hard or tedious task well done, even if there isn't any joy in the task itself. He didn't really want to do it, and I had to prod at him a bunch to see it through, but he sure seemed to like being able to say he built it himself, particularly after his friends told him how cool it was.

    I recall driving my own father nuts in the exact same way, and while I value the time he spent doing things with me now, I sure resented the hell out of him when he pulled me away from Speed Racer or He Man cartoons. So I'm taking the long view of things.
    Math is tough. Let's go shopping!

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