Tennis Ball Cannon with Clear Combustion Chamber

[hw97karbine] has made a pretty cool tennis ball cannon. While making a cannon of this sort is nothing new to us, we were impressed by the effort taken to get a stoichiometrically ideal mixture of 3.2% butane and air in the combustion chamber.

[hw97karbine] filled a syringe with butane and then dosed exact amounts into the chamber using a hole in the back. To control the air mixture he marked lines on the outside of the cylinder with magic marker. Simple but effective.

More rewarding than the methods was the cool slow-mo videography of the explosions in the chamber. You really have to check it out. [hw97karbine] shows clearly the difference between a well-balanced fuel to air mixture and a poorly balanced one. It’s one thing to say that more fuel does not mean better combustion, as we all remember from our personal potato cannon experiences, but it’s another thing entirely to see it.

[Via Reddit]

Your Fingers Will Never Leave Your Hands with This Firecracker Launcher

Who doesn’t like to ring in the New Year with explosives? But speaking from personal experience – I can neither confirm not deny nearly blowing my hand off once with a small dry-ice grenade – a hands-off way to launch your fireworks can be a plus, in which case you might want to check out this automatic firecracker launcher.

[Valentin]’s build has all the earmarks of an inspired afternoon of hasty hacking. Mostly built of wood and hot glue, there’s a feed ramp for fresh ammo and an elastic-powered sled on a ramp. Fireworks are metered onto the sled with one turn of a small gear motor, the fuse is light by a butane torch, and another gear motor pulls the sled back and launches the firecracker. The launch is somewhat anemic – perhaps some stouter rubber bands or latex tubing would provide a little more oomph. But it’s still a fun build with plenty of potential for improvement – perhaps something along the lines of this automated beer catapult?
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The Most Powerful DIY Railgun

The US Navy is working on a few railgun projects that will eventually replace the largest guns on the fleet’s cruisers and destroyers. These rail guns will fire a projectile away from the ship at around Mach 7 on a ballistic trajectory to a target one hundred miles away. It’s an even more impressive piece of artillery than a gun with a nuclear warhead, and someday, it will be real.

most-powerful-non-military-railgunUntil then, we’ll have to settle with [Zebralemur]’s DIY mobile railgun. He built this railgun capable of firing aluminum projectiles through pumpkins, cellphones, and into car doors and blocks of ballistics gelatin.

All rail guns need a place to store energy, and in all cases this is a gigantic bank of capacitors. For this project, [Zebralemur] is using fifty-six, 400 Volt, 6000 microfarad caps. The MSRP for these caps would be about $50,000 total, but somehow – probably a surplus store – [Zebralemur] picked them up for $2,400.

These caps are just the power supply for the rail gun, and aren’t part of the structure of this already large, 250 pound gun. Luckily, with the seats down in [Zebralemur]’s car, they fit in the back of his hatchback.

These caps are charged by a bunch of 9V batteries stuck end to end. When the caps are charged, all the power is dumped into two copper bars in the gun, accelerating the aluminum projectile to speeds fast enough to kill. It’s an incredible build, but something that should not be attempted by anyone. Although this does seem to be the year that all danger seekers are busting out their electromagnetic projection flingers.

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Making a Crossbow for the Zombie Apocalypse

Curious if he could, [Gignathiosis] decided he wanted to try building his own crossbow. So he did.

He built the entire weapon using hand-tools, minus a drill for the holes, though he could have gotten a brace for that bit. The most impressive part is that he used a hacksaw to carve up a block of aluminum into the trigger release — a job normally done by a mill. The only modern components on the bow is the limb (which he ordered off Amazon) and a bit of tactical rail for his scope. The end result is a gorgeous hand-made cross-bow.

There’s just something so satisfying about manufacturing old technology using hand tools. It probably has something to do with the thought that, if you ended up back in time somehow, you could use your 21st century knowledge as a hacker to change the world… and maybe become a ruler — or a magician — as long as you don’t do something that results in your entire existence vanishing.

Though if you really wanted to mess up history — take back a fully-automatic crossbow with you instead.

3D Printed Gun is Off the Rails

There are certain topics that cause people to have knee-jerk reactions: Try asking a crowd which Star Trek was best or–around here–take a stance for or against the Arduino and you’ll see what we mean. Certainly people polarize quickly when you talk about a 3D printed gun. However, if anyone can sneak [xtamared’s] 3D printed rail gun through airport security, then some guards will have to be fired. It looks like a cool prop from a bad movie, but (as you can see in the videos below) it can project a conductive slug into a decidedly low-tech target.

There aren’t many build details, although you can deduce a few things from the pictures and the captions. At the rear of the gun is a paintball tank that gets the slug moving before it hits the rails which further accelerate the projectile. The electric part is Arduino-based and the very prominent capacitors at the front end can deliver 1800 joules of energy (and add 20 pounds of weight to the gun).

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Make A Cheap (And Dangerous) Automated Flamethrower

Nothing lights up the night like a quick blast from a flamethrower, but there is a reason why you can’t buy them in the Halloween decoration aisle at Target. They are dangerous, for fairly obvious reasons. [Erco] seems to have no particular fear of death, though, and he shows how you can build a simple flamethrower with a small candle, a servo, Arduino and a can of hairspray. Tresemme Extra Strong Hold, in particular, although we don’t think the exact type matters that much. All he did was to mount the candle in front of the hairspray, then mount the servo so the arm presses the spray head down. The candle does the rest, lighting the highly flammable propellant in the hairspray to produce the flamethrower effect. [Erco] is using four of these, which are co-ordinated to fire in time with music.

This one seems a bit risky. Servos have a habit of locking, and there is nothing stopping these from locking in the open position, or sticking there if the Arduino crashes. A relay or other switch that reverts to an off position when the power is removed would have been more suitable here. Secondly, there is no emergency off switch. [Erco] has wired the Arduino up next to the flamethrower itself, so you are going to have to reach in to disconnect it. That is risky enough, but he also tried a 4-way configuration that would have been impossible to disable in the event of a problem (shown in the accompanying images). Thirdly, there is no fire protection between the can of hairspray and the open flame, so if the spray head melts or fails from the heat, it’s game over. Finally (and most importantly), where are the fire extinguishers? We’d like to hear how you’d build this with safety in mind. Let us know in the comments below.

We’re big fans of flames and explosions: we’ve have seen a couple of Survival Research Laboratory shows and were blown away by their destructive pyrotechnics. But, as SRL head Mark Pauline said in a recent talk, “when things blow up at an SRL show, it’s on purpose”.

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Anvil Firing: Awesome or Reckless?

The English language needs a word for “awesome and dangerous simultaneously”.

We recently ran into the strange pastime of anvil shooting on YouTube (where else?). The idea is that you pack about a pound (!) of black powder between two anvils and light it up. The powder explodes, and the top anvil gets shot into the air. Hilarity ensues, if everyone’s far enough away and wearing hearing protection.

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