Wednesday, August 17, 2011

Air Cannon!

So for my first blog, I figured I would use my air cannon project. I built this a while ago but I still pull it out of the garage almost every weekend to have some fun. 

     I got the idea to build this huge air cannon from my high school physics teacher. He built one out of steel pipe and used it to launch a bean bag a couple hundred feet in to the air. The air tank held 230 cubic inches of air. I of course wanted to build one that would put his to shame so I designed one that held 750 cubic inches of air (not the one pictured). It had a single tank and a 6ft barrel that was 1 inch in diameter. It was constructed completely out of scd 40 pvc with the exception of the brass ball valve and a steel pipes leading to the ball valve and the brass fittings for the gauge and the fill valve. I used 25 gal air compressor to fill the tank to 135 psi. I was a little worried about the "T" pipe fracturing so I covered it in electrical tape to prevent shrapnel.
     For projectiles I used half inch PVC with a steel lug in one end all wrapped electrical tape to attain a snug it in the barrel. These projectiles, when fired upwards can get so serious altitude. I'm to lazy to calculate it out right now but at about an 80 degree angle, I got flight times of 13 seconds!

     However It was a must to try a horizontal test for sheer power. A 2x4 seemed like a good test subject. As you can see from figure 1a it pretty much spit it in half! 
figure 1a

     This whole cannon idea has been coming along awesome so far, but I've always wanted a cannon that actually looks like a "cannon". So I started to plan out a new and very improved air powered masterpiece. My sights were set on a cannon that was so big that it had to be mounted on a carriage with wheels to even move. It also needed to have a barrel wide enough to fit baseballs, gatorade bottles or any other thing that may come about…like impact detonated projectiles. ..maybe  I Figured it also needed to have excessive power if I ever wanted to add barrel length or launch something really heavy. I decided to use a twin tank design to maximize the volume and keep the length in check. I planed on using a 10 foot barrel and at least that length in tank space so my design incorporated a fold between the barrel and the tanks. The new tanks are 6 feet long and 4 inches in diameter totaling 1809 cubic inches! That's a lot of air when its filled to 140+ psi! Each tank will have its own fill valve and gauge. This way I could use one tank at a time and hopefully get a few shots before it needed to be refilled. I still with a ball valve trigger system because the electric solenoids are only rated up to 80 psi. 

new tank compared to old.
     The new tanks are huge! By huge I mean probably too big…but thats crazy talk…OVER ENGINEER EVERYTHING!  When I built the smaller old one, before I attached it the barrel, I filled it up to 100 psi to check for leaks and then quickly released the air to feel how much force it could put out. It gave me a nice push but not enough to be impressive. I decided to do the same test on the new tank. Assuming that it would have a little more force, I took a more defensive stance. When I flipped the valve, the force of the air rushing out was enough to throw me off my feet and push me a good 3 feet through the air!  

     With all of the main components made the last step was to fit them all together, witch can be easy if the barrel was a couple feet long and I could support the entire weight and fit the two pieces together at the same time. I ended up having to suspend all the pieces from cross beams and slowly move all pieces together. After all the pvc was in place, I built the chassis and the wood cross sections between the tanks and the barrel. I got the wheels from an old circus wagon. They are completely lined with steel and are mounted on a solid 1 inch thick solid steel axle.

     Here is the finished product! I wrapped the barrel and some other parts in electrical tape, as I have found it really helps prevent shrapnel if anything were to explode. The cannon has exceeded my expectations and I will probably never get bored of it. I built this when I was 16. I'm 19 now, and still roll it out of the garage almost every weekend I'm home from college. The usual projectile I use is a gatorade bottle filled with water. How ever I have filled them with concrete. I have also shot railroad spikes(several at a time like a shot gun), hockey pucks(I glue 4 or five together to make a piston shape), long poles, flags, small impact detonated explosives, base balls, and even tanks of propane in to a bon fire! I have run some numbers on this thing and taken a few measurements… average projectile velocity is around 360 miles an hour! How ever that is the speed of a "full" gatorade bottle. Using that velocity and knowing the length of the barrel, I calculated the acceleration and used that to find the force that is exerted on a full gatorade bottle. So, in theory if I were to launch an empty gatorade bottle, it would accelerate much faster. How fast you ask? Well, the muzzle velocity would be somewhere around 1200 miles an hour. Almost mach 2!  

                                                            Here are some of the videos I've made…


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  2. looks good! I am trying to build one now and I was told not to use DWV fittings. Did you ever have a failure?