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    New steel ballista design...critque knowledge needed

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    ChronicCodez
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    Post by ChronicCodez on Thu Jan 03, 2013 12:00 am

    I currently only have one large bolt securring prods. Should I drill another hole in springs and use another bolt? Or is my design all wrong to begin with?


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    Post by Todd the archer on Thu Jan 03, 2013 2:43 am

    Very unusual design to say the least. I would put a second bolt on the limb so that they don't try to reverse themselves when drawn back.

    Honestly it does not look like the most effiecient design, but that is not saying it won't work.

    Keep us posted with your progress.

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    Post by shiloh on Thu Jan 03, 2013 5:38 am

    Very cool design indeed, my money`s on that it works, and I concur, another bolt to keep the limbs from pulling away from the frame.
    If you`re worried about compromising the limbs strength by drilling more holes, maybe peg the limbs on the outside, up through the frame against the limb to hold them in place.
    Cheers.

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    Post by kenh on Thu Jan 03, 2013 7:01 am

    I concur - at least two bolts, or as Todd sez, the whole thing could rotate and ruin your day! Will be interesting to see some performance specs - draw weight, power stroke, speed of optimum bolt, etc.

    Is that a Latchet style trigger mechanism you've got there?
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    Post by mac on Thu Jan 03, 2013 7:25 am

    ChronicCodez,

    I am also worried about the destructive and injurious possibility of the limbs rotating around on their mounting bolts while the weapon is drawn. I think that some means of preventing that is paramount.

    The other thing I see that you will want to attend to is the length of the string. If there is no tension on the string at brace, you run the double risk of stress reversals in the limbs and "sudden unstringing syndrome". A shorter string is what you need.

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    Post by Gnome on Thu Jan 03, 2013 9:03 am

    Wow, that is an interesting design. Is it inspired by anything pre-existing, or did you just come up with it? I think the concensus on additional limb attachment is unanimous, I'm wondering about the method. If you drill bolt holes you'll want to brace it externally with more steel, which leads me to wonder about using some kind of fitted clamp that would not require drilling holes through your limbs in the first place.

    Oh, and is the railroad spike in the photo as a scale reference, or is that what you're planning to launch with this monster?New steel ballista design...critque knowledge needed 499925

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    Post by ChronicCodez on Thu Jan 03, 2013 3:17 pm

    I myself am worried about eating one of the prods. I have some one inch plywood that I may triple up as a shield for testing. Over all design is pretty much my own. Made up of junk I have lying around. Prods are from my cultivator (a large rake that I pull behind my tractor). Stock is made from a teak board sandwiched in between two hard wood pallet studs. This allowed me to make the groove with little effort . I will alter it more later on.

    I have shims that I'm going to install in between each prod and wood. I believe this will pull the string taunt.

    I haven't made my trigger yet. I've been thinking an opposing tooth trigger. I thought I'd get some input before I continued. What you see in the picture is my slide that will grab cable and pulled back with a winch.

    I would rather secure the prods with a clamp but I am worried that they are too close to bottom of groove in the stock. Could the clamp only go through wood on bottom and wrap around prod? I'm not big on terminology yet so could someone tell me some things to google so I can better understand different styles of clamping prod to stock.


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    Post by Rizzar on Fri Jan 04, 2013 12:41 am

    Hey there.

    I was looking at the pics for some time now trying to think about an answer.

    Besides you need at least a clamp or a second bolt to prevent the limbs from rotating you would be well advised to wear some full body armour when testing the device!!
    Especially when using old used parts.

    Another point is, even if it works without breaking, you shouldn´t expect much performance: am i seeing it right there is some heavy metal on the back of the limb ends which is building the nocks??? (for security aspects it would be better to have it in front of the limb instead the back i think, but could be of little matter)
    So i think the cultivator blade´s (if that is the correct appellation) weight is wasting significant energy and with its position limits the working range of the spring.

    But you are sure these parts are from quality made spring steel?
    For safety reasons it would be logical for me to let these mountings break at some point instead of accelerating a stone to missile niveau when cultivating ground.

    As mentioned before, in bracing position there should be already tension on the string to prevent the limbs from bending in the opposit direction when shooting which would maximise risk of breaking.

    The shield is a good idea, you should put it into a "V" behind and to the sides when spanning and shooting the first dozens of shots.

    Coming to the trigger mechanism, since this seems to me quite big, why don´t you have a look at those roman siege arbalests and get some ideas there, i´d think this will look great mounted on a tripod with a spanning rail and (long) rope action trigger.

    Greetings Rizzar
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    Post by ChronicCodez on Sat Jan 19, 2013 3:09 pm

    Some updates...

    https://2img.net/h/i21.photobucket.com/albums/b295/ChronicCodez/image_zps85dbde44.jpg

    https://2img.net/h/i21.photobucket.com/albums/b295/ChronicCodez/image_zps73c7d979.jpg

    https://2img.net/h/i21.photobucket.com/albums/b295/ChronicCodez/image_zps3d0e32f2.jpg

    **Sorry, I can't remember how I posted images in first post

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