Step 9: Operation and Performance

Operation of the system is pretty straightforward. First, turn on the main valve on the CO2 tank and set the regulator pressure to whatever you want. Connect the gas supply to the launcher section and plug in the solenoid and the power into the console in their appropriate jacks. Turn the key on, flip the toggle, wait for the secondary chamber to fill, and "pull" the trigger. It's that simple. Once you let go/release the trigger, the cannon should automatically fill back up to the pressure set by the regulator.

On my launcher, the minimum operating pressure is about 20 PSI. Keep this in mind; if your supply of gas is less than your operating pressure, the gas can leak out. This would be really dangerous if you used a gas like CO2 in a closed space, not to mention frustrating as all of your compressed gas would be gone.

As far as performance goes, there are a lot of factors that come into play when dealing with distance, speed, etc. With the launcher itself, performance is really maximized by eliminating dead space - the space "in between" critical elements of the launcher. For example, the more space you have between your projectile and the main valve, the more your cannon's performance suffers. Moving the projectile as close as possible to the valve will result in greater power and acceleration. Since we used cam-lock fittings on this launcher, the performance will indeed suffer a little bit. However, I think the added functionality of the cam-lock fittings far outweighs the decrease in performance. Likewise, one needs to eliminate space between the main valve and the pilot valve. In this case, we did about the best we could, since the QEV and the DCV are back to back. 

If you think you want more power, you could always increase your operating pressure or get a bigger secondary chamber. I would recommend this if you were planning on launching large objects (larger than golf balls) over far distances. Just remember that you won't get as many shots out of the same CO2 tank as a launcher with a smaller secondary chamber. My choice of 2"x10" was "middle of the road" in that I can shoot golf ball sized objects as well as smaller things without penalizing myself in CO2 usage.
<p>What if you stored the secondary tank in the backpack as well, and just had a length of hose running from the QEV to the barrel. The electronics box would be attached to the back of the barrel, and wire would run from it into the DCV. Thoughts?</p>
<p>About how long did this take to construct</p>
<p>Could this configuration be used to launch a tshirt with any distance? Since it would only be used for tshirts, I'm thinking just a 2.5 inch x 12-18 inch PVC barrel attached directly to the QEV. I'm exploring this topic for the first time, and any help would be appreciated!</p>
<p>This is a youtube video of a similar gun, but using a .50 caliber muzzleloader barrel with power provided by an air compressor. I think the valve works the same.</p><p>https://www.youtube.com/watch?v=VfBRbSXM2Wk</p>
<p>instead of using a co2 tank could i use an 12v air compressor? like out of a 4x4?</p>
This is very, very impressive! I've got a couple questions about other possible projectiles: <br> <br>1) would it be possible to rig a barrel to fire a non-tipped arrow? (like a basic archery arrow that doesn't have anything attached to the pointy end. Or maybe something smaller and shorter, like a flachette? <br> <br>2) have you considered testing a barrel with a load similar to a black powder rifle? The average black powder ball (lead) is similar to a 50cal round, except its just a round lead ball. Since you wouldn't need powder, all you'd have to do is load it exactly the same way but just skip the powder load. You'd just need to pack the barrel with proper wadding and then drop the projectile in and pack it down. There's no real practical use for it, aside from the fact that it'd prolly be a blast to fire and would certainly get some curious looks from gunners at the range. <br> <br>One more thing: have you seen the wrist weapon that the black widow (Scarlett johannsen) used in the avengers? It looked to me like about ten individual barrels wrapped in a ring around her wrist that fired darts or flechettes. Do you think it's possible to rig up a smaller version of your design here to power something like that? <br> <br>Yours is without question my -favorite- kind of instructable because reading yours just gives me a flood of ideas and inspiration to work on something that I had either never considered or always thought was outside my comfort zone. Work like yours makes work like mine better simply by proxy! <br> <br>Well done! <br> <br>-steven
I'm very interested in the qev and camlock coupling that you used in this design. I have worked on several pneumatic cannons of my own ( at much lower pressures the your co2 tank ), and have had problems from the valves and connectors I used in my designs. For the most part my designs use modified diaphragm valves and npt thread fittings to connect interchangeable parts. I was wondering where you found the metal cased qev and the camlock fittings, as I can't find them locally or at reasonable prices online. Thanks.
Try McMaster-Carr. That's where I bought all of the components except for the 3 way valve. I bought it from Automation Direct.
This is amazing! I've always wanted to make a air cannon that refills itself. The instructables was very clear and complete. <br>
Great instructable. I really do hope you make my launcher attachment, I am interested to see how this 3/4&quot; QEV compares to a cheapy sprinkler valve. Try the tennis ball attachment, you need a pretty quick opening system to launch a tennis ball from a 2&quot; coupler. If you make the net launcher attachment I will definitely point the &quot;PVC will kill you&quot; commenters here. <br><br>It's hard to tell in the pictures but it looks like you have the quick connect Tee connected to port R in the Step 3 picture, but in the later pictures your assembled cannon appears to have it hooked to port P. Looking at the diagram for this DCV valve I think you want to hook to port R, this should allow CO2 to flow to the chamber in the solenoid relaxed state (port R to A), and fire (exhaust port A to P) in the energized state. This will make the electrical firing circuit simpler, just wire the NO firing switch and the NO safety key in series. The battery won't drain trying to keep the solenoid energized all the time. The system should be safer because you won't get an accidental discharge if the battery drains or a lead pops off.<br><br>Pneumatic diagrams are tricky, the use of open and closed is the reverse of the electrical meaning. A normally closed electrical device allows current to flow completing a circuit, when actuated it opens and blocks current. A normally closed pneumatic/hydraulic device is off (think of closing a valve) blocking flow, and when opened allows the gas or fluid to flow.<br><br>One last thing. It is possible for the CO2 regulator to fail, that would dump 900+ psi into the gun. I am sure the air hose or clamps would fail and act as a relief, but you could replace the tee with a cross and put a real relief valve there.
The DCV is a very cheap indirect acting solenoid valve. In it's relaxed state, the CO2 cannot flow into the pressure chamber. Direct acting valves would indeed simplify the electronics for the cannon, but I wanted to use parts I already had as much as possible. If I ever had to remake this cannon, I would most definitely use a direct acting DCV.<br><br>The CO2 regulator that I am using has an inline safety pop-off valve, which is nice. Nobody want's stuff to burst on you.. That wouldn't be good.<br><br>I'm close to finishing your net gun attachment. Im so excited to try it out! Hopefully I'll finish it soon, but all of that engineering homework comes first.
Thanks for pointing out the different type of solenoid valves, I had no idea. I am guessing that the way the internal piloting works prevents the pressure inlet from being moved to a different port. You probably saved me some wasted dollars and loud swearing.<br>
nice cannon, I can see you have almost perfected it, the only thing you can improve is to make it auto load and I think longer barrel would give more power. I have a combustion cannon myself and the bad thing with it is that it takes long to load and its boring to wait, the fun part was the construction and testing. <br>P.S. how much did it cost in total?
I completely agree. The golf ball barrel is breech loaded and the nerf barrel is soon to be of the same design. I did not want to make a true semi-auto since I would most likely need to set the bore/barrel to a specific one. I wanted versatility. However, it is still possible to do semi-auto. I'm definitely going to try when we build our new lab here. For this project I had to buy all of the tools (pipe wrenches, adjustable wrenches, drill, drill bits, etc.) since I can't use University equipment for personal projects. This added to the final cost. Overall it probably ran me around $400, including the equipment.

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Bio: I am a mechanical engineering student at the University of Alabama. I love to build whatever interests me. I especially enjoy merging machinery with electronics ... More »
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