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This little cannon is powered by bursting a rubber diaphragm with a bicycle pump. I cut the diaphragms from an old bicycle inner tube. You can double them up or burst one at a time. It uses 40mm foam practice golf balls for ammo. You can also use it with just the pump but it doesn't fire with near as much force.

This is not my original idea. A few years ago I saw this rocket launching toy on TV. If you make this you could use the same replacement diaphragms.

UPDATE: Apparently you can use more than just a rubber diaphragm. I've also tried duct tape and aluminum foil. It works great.

Step 1: Get the Parts

Plumbing parts come in all shapes and sizes. These are no different. You could make the same set up bigger or smaller. You could even modify the barrel for a smaller diameter and use it for paper rockets. What you see here cost me $14.00.

You'll also need a base and a way to attach it. I'm using the base form an Estes launching pad. The support bracket came from an old portable fan.

Step 2: Install the Valve Stem

I started by drilling a pilot hole with the end cap mounted in my lathe. From there I moved it to the drill press and drilled it out with a 1/2" bit. I used sand paper to ease the edges of the hole.

Having a valve stem tool is helpful but not critical. Before pulling it in place I added a little grease to ensure a proper seal.

Step 3: Screw the Parts on

Since only one side is pressurized you only have to worry about a seal at the valve stem and at the threads to the end cap. Before threading the cap into the union coupler I applied silicone grease. For the exit side I simply threaded the adapter on hand tight.

Step 4: Prep the Barrel

I cut a section of pipe about 3" long. I then used a razor blade to round over both the inside and outside edges. This allows the foam balls to load without getting caught up. To smooth out the finish I used sandpaper. All that's left is to push the barrel into the adapter.

Step 5: Cut the Diaphragms

This part is pretty straight forward. Use a pair of scissors to cut a section of bicycle tube out. Unscrew the coupler and use the male half as a template to cut a disc out.

Step 6: Testing... Testing

Without a foam ball in place this cannon is "call the police" loud. Check out the video and you'll see the air burst push the camera back (see the intro video at 1:05). Out of all the discs, only one ruptured with a slit. All the others took a star shape. Sometimes I'd see pieces of inner tube in the barrel. So keep in mind more than just a foam ball could come flying out. Don't shoot your eye out.

Step 7: Mount the Cannon

I used the bracket of an old portable fan for a mount. I hot glued it on and added a couple zip ties for support. The base is an Estes model rocket launch pad. After a little machining on an aluminum tent stake it fit right in the base (see the last picture).

Finally I painted it with rubberized undercoating.

Step 8: Launching Ammo

The barrel has an inner diameter of 35mm while the foam golf balls are 40mm wide. This makes a snug fit which is great for launching. While I'm using an old bicycle inner tube for diaphragms you could also use these.

It works without the diaphragm but it doesn't go as far. As tempting as it might be, don't shoot other people with this.

Thanks for reading.

<p>This is very cool! I have been experimenting with various compressed air cannons, and I have found that a electronic sprinkler valve is very effective when releasing large quantities of air!</p>
<p>The other posts reflect my feeling as well, you have a very nice project. I want to recognize you for the effort that went into the documentation! Clean, concise and obviously well thought out. The pictures make it very clear what you explained so well in your text. Truly, &quot;An Instructable that doesn't require deduction&quot; .</p>
<p>Very cool!</p>
<p>Very nice, the next upgrade would be an 4&quot; dia x 12&quot; long PVC pressure tank connected to an electric sprinkler valve connected to your cannon. Pressure could be attained via your foot pump or air compressor.</p>
<p>I've used a sprinkler valve as an air pressure solenoid and I can confirm this would be a good approach. You'd definitely want an accumulation chamber just behind that valve to build up enough air to push the ball out forcefully.</p>
<p>Are you cutting section of bicycle tire or tube? Picture shows tube text says tire.</p>
Tube. Sorry about that. Fixed it. Thanks!
<p>I'm sure it wasn't on purpose but I got it the first time:)</p>
<p>Great idea, any idea how many psi it takes to rupture the inner tube?<br>Also for more speed and accuracy fit a larger barrel.<br>I built a ping pong Cannon featuring a vacuum and burst dusks, but I've never seen a burst disk used with just positive pressure before, most people use a PVC ball valve, does the bust disk work better?</p>
<p>PVC ball valve tends to be a slow release pressure = less power delivered. Burst disks fail catastrophically for a quick release of press and a lot of power. The downside is that, unless you have great quality control on disk, build, and use, you lose some control over the amount power and when it's released.</p>
<p>Yes! Finally another design with a burst disk! Never seen one use rubber before, kudos. I have my own version I posted a little while back that's a bit...fancier I suppose. It has a trigger system, versus the failure system here. Feel free to check it out and combine different ideas with this type of launcher. https://www.instructables.com/id/Cascade-Failure-Triggered-Double-Burst-Disk-Pneuma/ </p>
<p>Very cool. Aluminum foil worked great for a diaphragm. Thanks!</p>
<p>&quot;It works without the pump but it doesn't go as far. As tempting as it might be, don't shoot other people with this.&quot; you mean without the diaphram? not pump right? </p>
<p>Good looking out. I fixed it. </p>
<p>Nice job! I bet some heavy aluminium foil would work quite well as a disc also.</p>
pretty cool. @ kaiven- that is similar to some of the 'tater gun designs i have done in the past.
<p>AWESOME! When I saw this on the homepage I was like &quot;Whoa!&quot; :D</p>

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Bio: Awesome Gear I've designed myself.
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