Instructables
Make a simple cannon out of some tube and a vacuum cleaner.

Step 1: Find Materials

Find a length of tube. PVC or cardboard tube will work. Make sure you will be able to hook up a vacuum to somewhere on the tube, but not the end holes. Then find any ball that is close to the inside diameter of the tube.

Step 3: Test It!

Place the tube on a horizontal or angled surface. Put the ball in the tube, then press something (newspaper, plastic, etc.) on each end. Start the vacuum and it should hold the seals on the end. Remove one of the seals and the ball should fly out the other side. Depending on how you did it, the ball can have a lot of velocity, so be careful.

Play with the different types of tube and the length and diameter of the tube. Some will work better than others. Change the type of projectile, too. For some fun, try shooting marshmallows or mini marshmallows. There are endless possibilities with this project.
 
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Mr_Rep3 months ago

What would be the best way to put a one way valve on the barrel, so that the barrels seals after each shot but doesn't interfere with the projectile too much?

weldor3 years ago
This device is what is often referred to as an "air ejector" and can also be used to move fluids. A simlar device can be made using a garden hose instead of the vacuum and it can be used to move liquids, They are both used on board ships. The first unit is powered by steam and is used to remove pressure/creeate a vacuum in certain steam powered equipment. The second one I described is used to dewater the bilges and tanks. I know this from first hand experience. I spent ten years in the US Navy operating anda repairing shipboard machinery and equipment. Anchors Aweigh!
I'm not so sure...

An air ejector uses the Bernoulli effect to suck up/eject fluids while the above "cannon" simply creates a partial vacuum and uses atmospheric air pressure to accelerate the ball.

While the effect is pretty much the same, a better analogy for an "air ejector" version of this would be using a leaf blower to push air through the tube, and then dropping the ping pong ball in an opening in that tube to be accelerated by the air blower.
without building one, it's hard to tell what principles this is using. if the ball is being pulled through the tube directly by the vacuum, it's pretty basic. however, if the suction on the far end is a result of the air flow at the end connected to the vacuum end, it's operating on the venturi effect. the name of the equipment he's talking about in the navy is an "eductor" i'm also in the navy, they're used for removing water from spaces after fires, or just general plumbing.
One year after I post a comment XD

After some serious thinking and a little dusting up on my physics I can sort of see how it could work through the venturi effect...though I'm not sure how well it works when the air has to turn a right angle like it would in this cannon. I suppose both sort of effects could be at play. Perhaps if we made different cannons that try to use primarily one principle or another maybe we could isolate which phenomena might be more at play.
singhjr961 year ago
imagine if you have this concept with a tiny motor, a tiny tube, and a de laval nozzle and a barrel. you could make a quite powerful cannon out of it. or more specifically as i was thinking a paintball gun. depending on how fast you could get rid of the air in the tube, and if you could even find a way to open and close the vacuum tube quickly and efficiently. and pump that air through a tiny de laval nozzle. basically making a tiny one man small portable air ejector.
would this work if you used a elbow and another pvc pipe to make it an L shaped cannon, Im trying to build a paintball Milsim Mortar, to sell so I can by equipment for my 3 man speedball team (paintball)
ALogan973 years ago
I'm definitely trying this as soon as i get some PVC. It would make a great base for a new Nerf rifle I'm building
cool bike
hapman95 years ago
dont vaccums suck stuff up
ilpug hapman93 years ago
they do. The whole premise of this cannon is that the vacuum creates a vacuum in the tube, and then air is allowed into the tube, propelling the ball out as it rushes in to fill the vacuum.
hapman95 years ago
Message me back cuz i dont really get it........ and i wanna try it out
The way i understand it is that the vacuum cleaner creates a vacuum in the tube due to both sides being covered. Then, when the paper on the side that the ball is on is removed, air is sucked in to the tube (from the side of the ball) to fill the lack of air in the tube, thus propelling the ball to the other side of the tube because the other side is still covered, and breaking the other piece of paper.
So really the vacuum cleaner isn't pulling the ball to the other side, the incoming air pushes the ball.
danm955 years ago
Im realy tempted to make one of these and tall my little brother to put his hand over one end then mine over the other then move my hand and shoot him(LOLOL) >: )
danm95 danm955 years ago
*tell
iq_abyss5 years ago
Does this work off of a ventury effect?
I saw one in my science class but with a 2" pvc pipe called a ping pong cannon; its pretty loud, it shot right threw a soda can. Dangerous but cool.
y2kkmac7 years ago
Even though this may sound odd, use gorilla tape! It makes a kindofifyouwantittoobereallygood difference. Also, make the opening for the long tube (where the vacuum takes air in) large, and put a steel/iron/whatever mesh covering on the hole.
tyeo0988 years ago
I made one with a makeshift onway valve on one end and a hopper on the other, materials: duct tape dixie cup card board
debben8 years ago
Cool stuff. I did something similar for a friends stage-show to shoot confetti. Also when i made a potato canon i put a pressure relief valve to make sure i got enough psi.
Fark 21118 years ago
This cannon is really cool. But still, if there is a magezine, how fast can it shoot?
Intense! Great contribution.
This cannon sucks! literally! no, but on a more serious note, sweet project :)
unclepunchy8 years ago
ah, i belive its a Bultaco Alpina...74ish? i got a 75 'Taco Sherpa T and they got a different tank... but we digress :P the cannon.... nice job!
ehmbee8 years ago
Anyone riding a vintage Bultaco can't be all bad....neat project, can't wait to try it out with my buddy's 11 and 13 year-old evil geniuses, or is it genii?..MUUAHAHAHAHA!
radiorental8 years ago
that looks like squid-labs/instructables HQ
elemenoh8 years ago
Yeah! Great project but I have to admit that bike is a bit distracting... in a good way. :D
brob8 years ago
Awesome. I'm digging the rather large looking workshop/garage space too. I wish I had that luxury. I have to use my dining room for projects.
courtney8 years ago
That's a Bultaco. I'd say early to mid 70's flat track bike, probably a 350cc Sherpa.
Awesome!

http://epll.no-ip.com/Bultaco/miquel/Bultaco/lbultaco.htm
mattgyver8 years ago
Definitely will try this! Also, to satisfy my curiosity, what kind of motorcycle is that?