[JoergSprave] has done it again. His latest, most ridiculous weapon? A Gatling gun that fires crossbow bolts, using compressed air inside coke bottles — and an electric screwdriver.
For those of you not aware, [Joerg] is our favorite eccentric German maker, a purveyor of slingshots and all things ridiculous and weaponised. He runs the SlingShot Channel on YouTube, and has graced us with things like a slingshot cannon (firing 220lb balls!), a machete slingshot for the upcoming zombie apocalypse, and more.
Each coke bottle has a quick release pneumatic air valve, with a wooden lever attached to it to make opening the valve easier and quicker. The coke bottles are pressurized separately using an air compressor, but can also be filled using a bicycle pump — he got his hands on a pump capable of putting out 300 PSI! Word of safety though — you really don’t want to use coke bottles as pressure vessels — but [Joerge] is crazy so we’ll let it slide.
The bottles are then mounted on a ring which is rotated by an electric screwdriver. As the bottles spin around, the wood levers catch a curved surface, forcing the valves open, firing the arrows at approximately the same location every time. It’s surprisingly powerful, low-tech, and accurate.
[Thanks WickedMongoose!]
I think that soda bottles make a perfect reservoir for this application. What will happen if it does explode? You’ll have light weight crap flying around that will be stopped easily by friction with the air. Contrast that with a heavy PVC pipe (no no nooooo) or a steel reservoir that fails – sharp pieces that can really hurt you flying in all directions.
He really should be wearing a face shield and ear protection though.
Clearly spoken by someone who’s never filled coke bottles with dry ice and water… (don’t try it at home kids)
Yep, I still have a scar on my leg from that light weight plastic that is easily stopped by the friction of the air. and it was significantly further away from me than the bottles in this arrow shooter.
What kind of bottle were you using? I’ve done it many times and admittedly, been lucky, but curious what kind of plastic bottle it might have been that was able to maintain that kind of speed/penetrating power?
Also, coke bottles are made to hold in carbonation.
He should be wearing a face shield and ear protection!?!? This is a man who made a frikin’ arrow gatling gun, the massive cloud of testosterone this demigod of awesomeness exudes is more than enough to protect him from nuclear bombs, never mind exploding pop bottles!
Very irresponsible thinking right there.
Wrap some duct tape around that and that would solve most of the shrapnel problem.
When PET or PETE breaks it tends to shear in such a way that the edges are beveled and very sharp. Most of those bottles are actually multiple layers with ‘virgin’ new on the inside, a gas barrier to keep CO2 in and O2 out, and the bulk of the sandwich is the outer layer that contains a lot of recycled plastic from old bottles.
Dentists use 2liter plastic bottles pressurized to 130 psi 24/7/365 in the spit sink. I hear they can go to 180 eazy peazy
Disgusting that a medical operation is conducted without suction, requiring the poor person to get up and spit. Disgusting!
What is such pressure used for anyway.
Nevermind the bottles exploding, the bolts look like they could do some serious damage to a human target.
piotrsko, I would say you heard correctly. I used to pressurize 2 liter Coke bottles all the time with a hole drilled in the cap and bicycle inner tube schrader valve pushed through. With a 1/3 of the bottle filled with water and then compressed air, they make a hell of a rocket. Alternately I would fill them with air only and shoot them with a pellet gun for a very loud bang. 180 psi was the highest my compressor could handle and the bottles were under so much pressure that thumping it or dropping it would sound like glass being struck. Even after repeated cycles of pressurization and depressurizing, I never had one fail, but some safety equipment is never a bad idea.
I even spiked some pressurized bottles on the concrete with all the strength I could muster and still never had one fail. They sure would bounce way more than you expect though.
We used to do the same thing when we were kids. Our compressor only went up to 120 psi though. You could smack it on your knee when pressurized and hear it ring like a wine glass. I never had one fail either.
They can be used “safely enough” as a pressure vessel for hobby applications, in my experience. You’ve gotta know the risks you’re taking though.
One thing to note is that not all soft drink bottles are made the same – and the designs are continually improved by manufacturers trying to cut down on material costs or other factors. So a bottle might take 200psi, but the Coke bottle of tomorrow might not.
We need to regulate coke bottles!!! Coke bottles are too dangerous for our nation’s people.
All jokes aside… This project is awesome…. This is certainly a guy I wouldn’t want to mess with.
I neglected to take into account the energy stored in the air. Am I reading this correctly: http://www.tribology-abc.com/abc/thermodynamics.htm
with a 2 liter chamber, 200psi (1.378Mpa) gives 3600 joules (or 7200 – I don’t understand the units difference yet). That seems excessive – is that really how much energy is stored in the coke bottle at room temperature?
That guy’s laugh is enough to send you running for cover.
Joerg Sprave is awesome :) and I think he knows what he’s doing, or at least experience :D
If you shrink a coke bottle using heat (like hot/boiling water) you will increase the wall thickness.
It works out that the volume decrease is directly proportional to the hoop stress in the bottle wall at the same pressure (i.e. shrunk volume = n% start volume and shrunk stress = n% start stress).
This improves your safety factor at the expense of holding less air which may not matter as much in a single shot device such as this due to the barrel volume being much less than the tank volume.
You could, of course, use this stronger tank to increase the pressure but that makes things less safe should they go wrong.