Bungee Bazooka... Joerg-ified?

Discussion in 'General Slingshot Discussions' started by Cylvre, Oct 17, 2011.

  1. Cylvre

    Cylvre New Member

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    So the other day I received the weekly newsletter from Instructables<u></u>, my favorite DIY site, and one of their features projects immediately caught my eye: The Bungee Bazooka (as a new member I'm not allowed to post links to outside websites, but a search for Bungee Bazooka on the Instructables website should yield the relevant post). I looked over the build and while it's an excellent DIY build guide the performance of the final project, lobbing one of his homemade darts about 100 feet, left me wanting more. I immediately thought of Joerg's recent bullpup sling-rifle, which uses a similar design, and wondered how I might go about scaling up the flatband and roller system from that and combining it with this Bungee Bazooka.<br><br>So I've spent this morning combing through the forums here and learning a lot, but as often happens when diving into a new pool of knowledge I also have yet more questions as well. Most of my questions (and it seems like this is very common) are dealing with the rubber, but hand-in-hand with that are concerns about the structural integrity of the device with the scaling up of it's power.<br><br>When it comes to banding size the most useful information I've found is what Joerg posted on this thread: <a href="http://theslingshotforum.forumotion.com/t470-band-lengths#3915" class="postlink">http://theslingshotforum.forumotion.com/t470-band-lengths#3915</a> From what I'm reading there, and going by the dimensions within the instructable which calls for a 5 foot (1.5 meter) pipe, the draw length on this beast is going to be just under 10 feet (3 meters!!) which by my understanding would then put my band length from 3 feet 4 inches (1 meter) down to 2 feet (~61cm) depending on how powerful or long-lasting i want the bands to be. The immediate problem I see there is that even when the device is uncocked and fully "at rest" the rubber will be under tension, since the bands will be shorter than the pipe, and therefore will loose power after a time. This is a problem Joerg mentions in his post about the pros and cons of using rubber on crossbows:<br><br><i>"<strong>Must be kept relaxed</strong>. Rubber looses power quickly in <br>drawn out condition, so you should not cock a slingshot crossbow and <br>then wait a long time before you shoot. Now this can be compensated by <br>using heavy rubber, and also the rubber "heals" quickly (full force is <br>back after 15 minutes if you relax the bands again), but this issue is <br>serious for hunters."</i><br><br>Even beyond that issue I'm not sure how many band layers of TB Gold would be best to use in a device this size. Since it's a 4 inch (~10cm) PVC pipe I figure 2 inch (~5cm) bands would be able to be used which at one band per side would mean a minimum draw of about 26 pounds (12 kg), two bands makes about 52 pounds (24 kg), three bands up to 78 pounds (36 kg) (numbers figured from information in the above linked post, I could be confused and completely wrong about them). For larger, varied ammunition (tennis balls, rolled up t-shirts, snowballs) is there any kind of rule-of-thumb to go buy for draw weight?<br><br>Then as the draw weight climbs up I wonder if just the PVC pipe walls (only 3/16", about 4.8mm) will be strong enough to withstand the tension in the bands or if it would be prudent to instead create a stronger structural framework around the pipe that would absorb the power/tension of the bands and just have the pipe act as a guide or "barrel".<br><br>So what do you think guys, would it be easy to upgrade this project into a more powerful device, or have I thought myself into a complete redesign that maybe in the end would be more effort than it's worth?<br><br>Thanks in advance for any ideas/comments/suggestions you have (and sorry for the short novel of a post!)<br><br>~Chris
     
  2. Ryan Wigglesworth

    Ryan Wigglesworth Senior Member

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    <a href="http://www.instructables.com/id/Bungee-Bazooka/" target="_blank" rel="nofollow">http://www.instructables.com/id/Bungee-Bazooka/</a><br><br>This is pretty cool, we need to *Joerg-ifi* it though, like you said. This thing needs to shoot giant lead balls the size of tennis balls <img src="http://illiweb.com/fa/i/smiles/icon_twisted.gif" alt="Twisted Evil" longdesc="13"><br><br>I think you should use wood, instead of the tube that they use, or a stronger version of pvc tubing, the thick black stuff perhaps.<br><br>NERF BULLLETS LOLLLLLLL
     

  3. JoergS

    JoergS Administrator

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    Found a video of the guy shooting it:<br><br><embed pluginspage="http://www.macromedia.com/go/getflashplayer" src="http://www.youtube.com/v/93ODwV5-XO8" width="425" height="350" type="application/x-shockwave-flash" wmode="transparent" quality="high" scale="exactfit"></embed><br><br>I think that the weapon would shoot harder if he would shorten the bands and attach the ends much closer to the muzzle, so that they are fully stretched to 550% in loaded condition.<br><br>Also the tubing creates friction, which means he looses a lot of speed. I can shoot a tennis ball a lot more far, and faster, with my howitzer (as seen in the Venus Williams video). <br><br>This reminds me that I always wanted to make a bottle shooting slingshot<br> crossbow... It would look fairly similar, just with much more rubber and a front hook, so you can slip the muzzle over a fixed object (rail or tree branch), then pull back the bands with both hands and walk backwards to cock it. I think I can throw a half full coke bottle about 100 or 150 meters. <br><br>I would of course only put some colored water inside of the bottles, but in theory people can add a lighter, turning the weapon into a molotov shooter... which may cause trouble.
     
  4. PandaMan

    PandaMan New Member

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    I would love to see a bottle shooter. I assume you would test both plastic and glass bottles?<br><br>PandaMan
     
  5. tayloriand

    tayloriand New Member

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    Hi Cylvre,<br>This is a great post and perfect for this forum.<br>In addition to admiring beautiful wooden slingshots I'm sure many - like me - have a stupid big smirk on my face (and a girlie giggle) when they see a rubber band powered device launching projectiles at inappropriate objects.<br>Cheers<br>Ian
     
  6. Cylvre

    Cylvre New Member

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    I'm glad at the positive response! I'm already plotting about how I will be going forward with this...<br><br>Joerg, I do have one question about what you said. When you talk about the tubing creating friction are you referring to the large pipe that serves as the "barrel" or the smaller ones which he has the rubber running through on the outside to prevent it from snapping back?<br><br>I like the look, and minimal safety feature, of partially enclosing the release and sling within the large pipe as this design does. Makes me feel less wary of a band snap or having an object "explode" when fired and making a huge mess (like a tomato, or egg). If having the ammunitions slide on the inside of the pipe would reduce the efficiency of the slingshot I may have to consider having everything "float" inside of the pipe and just keeping it as an aesthetic feature rather than a structural one.<br><br>So many ideas... To the drawing board!
     
  7. JoergS

    JoergS Administrator

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    The "sliding" of the ammo in the PVC pipe is the cause for the friction. If you let it float freely, there is no such friction of course.
     
  8. petersonOD

    petersonOD New Member

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    Cool design. I agree there could be a few improvements.
     
  9. SkauneJohan

    SkauneJohan Member

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    would love for a Jørg version of his bazooka <img src="http://illiweb.com/fa/i/smiles/icon_twisted.gif" alt="Twisted Evil" longdesc="13">
     
  10. onnod

    onnod Im from Holland, isnt that weird?

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    the bottle bazooka would be cool idea <img src="http://illiweb.com/fa/i/smiles/icon_twisted.gif" alt="Twisted Evil" longdesc="13">