Introduction: 15-Minute Snow Hand Cannon
It was a normal Winter day in Buffalo. The sky was cloudy, the air was chilly, and the precipitation was rapidly changing from chunks of slush to fluffy lake-effect snow.
Snow is fun. You can walk on it and make things with it and hurl it at your friends; that is of course, if you have willing fiends and any sort of physical coordination. While I had a bunch of friends handy, I was severely lacking in the ability to move snow downrange with any sort of distance or accuracy. As an uncoordinated engineering student, there was only one solution: make something to do it for me.
This instructable details the making of what is affectionately called "The Snow Hand-Cannon" by those who have seen it in action.
It needed to be cool (and not from the weather), it needed to be made out of things I had (college dorm tech), it needed to work, and it needed to work now. With little in the ways of materials and less in the way of tools, this is the coolest way to move snow.
The end result runs on air pressure from a bike pump and can chuck snow-bullets a bit farther than the average person's maximum throwing distance.
This is a gun. It shoots things. Although I've shot it at people and been shot with it, if the projectile isn't ONLY SNOW, it could be dangerous or even deadly. Ice chunks or rocks aren't allowed. Don't point it at anything you don't want to shoot even if it isn't loaded. A bit of debris in the barrel could be the next projectile.
PVC is brittle, especially in the cold. Don't drop it on hard objects while pressurized and be careful (Safety glasses, etc.) when pressurizing it.
Step 1: What You Need
1"x~30" PVC pipe**
1*x~12" PVC pipe**
Repair kit bike pump (or floor pump)
Plastic grocery bags
A stick (narrower than the inside of the PVC)
A chunk of foam or something around 2-3" cube (5 cm cube)
** The length and even the width are approximate and mostly governed by what I had available. I've tested it with a smaller pipe and it still works and I assume the same is true for slightly larger diameter. One pipe needs to be at least twice the length of the other, preferably more. When I have money and I can go to a Home Depot, I want to make a super-cannon that's actually a cannon size.
Hand saw or chop saw (to cut the PVC if necessary)
Sandpaper (medium to rough grit)
Step 2: How It Works
The limited time and resources favored a simple, practical design. The gun uses no valves and no mechanical trigger. You just pump air into a pipe that's sealed with a plastic grocery bag and when the pressure gets high enough, it pops and the air goes out and carries a packed snow chunk with it.
The plastic bag is held in place by simply putting it between the barrel and the T-joint when you put it together. Everything else is held together by duct tape.
Step 3: The Pipe: Part 1
Take the long piece of PVC pipe; this is the pressure chamber. The reason that we use the long one as the pressure chamber is that the larger volume is more effective in transferring energy to the bullet for any given initial pressure.
Duct tape the crap out of one end of the pressure chamber. It's important that there are no leaks here, so take your time and make sure the tape is sealing against the pipe. I used around 8 layers, but more couldn't hurt.
It's the pinnacle of pressure-vessel technology, I know.
Step 4: The Pipe: Part 2
Take the shorter piece of pipe; this is the barrel. Sand the ends so that the sawed edge doesn't cut the plastic bag. I was too lazy to sand both ends, so I just marked which end I sanded with a bit of electrical tape.
Again, it's pretty simple. If you thought projectile weaponry was complicated, I'm here to prove you wrong.
Step 5: The Pump
The bike pump doesn't currently connect to the pressure chamber. We could be all fancy and put a Schrader valve in it, but I didn't have one nor did I have the time to get one. The snow needed to be launched NOW!
That's where the T-joint comes in. Tear the duct tape lengthwise into halves or thirds and wrap it around the pump's output until it matches the inner diameter of the T-joint. I added a final layer of masking tape so that the duct tape wouldn't get torn up when I took it apart again, but that's optional.
Take your time and get the duct tape exactly to the size of the T-joint. If this doesn't seal well, the gun will be finicky if it works at all.
If your pump output isn't circular or is too wide, you can get a 1" (3 cm) length of plastic pen body or a bit of narrow tubular metal that's approximately the same diameter as a bike valve (or a bike valve, I suppose). Anything hollow that fits in the pump is good. Just wrap the duct tape around that instead of the pump and connect that to the pump. All we need here is for the pump to connect to the pressure chamber through the T-joint. If the pump matches the outer diameter of the T-joint, you might get away with simply taping the pump to the T-joint. It'll go on the middle opening of the T.
Step 6: The Bag
You want bits of bag that are 3 layers thick. One layer can't hold all that much pressure and 4 layers sometimes holds the pressure too well and the barrel pops off or something breaks. 2 could be better for a controlled safety version, but 3 has been empirically determined as the optimum number for reliability and range.
It's hard to operate plastic bags with mittens on, though, so I made a bunch of 3-layer bundles to speed the reloading process.
Cut the bag into strips a couple inches wide (4-5 cm). If you're careful, you can keep the side portions where the handle and the bottom seam hold four folded layers together. Cut off one layer and the remaining 3 will stay together.
With the strips that didn't come seamed together, just tape them together three layers thick.
Step 7: The Stick
You want a straight stick without knots that fits inside the barrel. You will use this to pack the snow into the barrel to make a snow bullet. Use your knife to cut off any sharp bits and extra branches. My stick was a bit too thin at the end, so I wrapped duct tape over it until it was the correct diameter. You can put a big wad of duct tape over the other end so it doesn't jab your hand when you're packing the snow.
Step 8: Assembly
Take the chamber and insert it into one side of the T-joint. Push it in tightly and duct tape it on so that it doesn't come off before the bag pops.
Take the duct-tape wadded bike pump and insert it into the middle of the T-joint. Duct tape around the seam to ensure a seal. Tape around the whole assembly to keep the pump from popping off under pressure.
Take a piece of styrofoam (or anything, really) and tape the pump parallel to the chamber. If you have a floor pump, you can skip this bit. This just keeps the pump from wobbling around as you try to fire.
Put the 3-layer bag piece over the open end of the T-joint and press the barrel (sanded end first) into the joint so that it holds the bag. Twist the barrel in well so it doesn't shoot off under pressure.
Step 9: Test It
Point it at something that isn't alive or fragile. Pump.
There should be a loud pop (surprisingly loud when you don't put a projectile in).
With my little pump, it takes about 9 full pumps to fire.
Sometimes, you can overcome a small leak by pumping really fast. As long as you can get the pressure high enough, it'll work. In any case, if you can't feel a bit of resistance in the bike pump, you have a leak.
If the bag doesn't pop, check the end of the chamber for leaks and put more duct tape around the pump-T-joint connection. Make sure there aren't wide creases in the tape where the air can escape.
If it still doesn't work, check that the bag didn't get cut as you pushed in the barrel. Sand the edges of the barrel more or try a different brand bag. I used Wegman's and Dash's bags. They're thin, a bit stretchy, and tan and advertise their recyclability.
Once you can get it to pop reliably, it's time to go outside.
Step 10: The Snow
Take the barrel and scoop it through the snow so it's full of loose snow. Put one end of the barrel against a wall or sidewalk (or even your hand) and pack the snow down with the stick using it like a ram-rod.
If the snow packs well, you should get a good, solid chunk. Depending on the snow density, the bullet might be too big. If the snow bullet is more than a couple inches long, push a bit out of the barrel and break it off.
There should now be a bunch of packed snow at one end of the barrel (preferably the end you sanded).
Step 11: Wreak Havok
Put the snow-bullet filled barrel into the T-joint with the plastic bag like in the test fire. Point. Pump. Enjoy!
Although it's reload rate is a bit slow, it'll definitely be much more awesome than anyone else's launching method and there's a good chance it'll fire farther than people can throw. It's also more accurate at long ranges once you've found a good way to pump without moving the barrel. Rain snow-bullets down on your enemy's fort from beyond their throwing range.
Just don't go disturbing traffic or wounding innocent passers-by. Don't shoot anyone point-blank or in the face. Don't get hurt or hurt anyone, yadda yadda. See the disclaimer in the intro.