300 psi pneumatic, a couple questions

[bravootome]

Just look the other way when owerride your tank. And fill it in open air.

you may never know when it will blow up if you only test it.

[wdr0]

Hey, just want to let you all know I have not abandoned this project. However some of the fittings have not yet arrived and I starting college so it may be a bit before I get it done. It will happen though, I have already invested $400 in parts. I was expecting to have the fittings sooner so I could have it done before school.

[wdr0]

Hey everyone, I have assembled the cannon and tested successfully up to 80 psi. I think it would be best to take it out of town for higher pressure tests, so I am not sure when I will do that. I also need to make a better piston I think for the higher pressure tests. I will get some pictures up in the next couple days. I ended up with the 2" barrel 15ft long, and around the same length for the air chamber. It put an empty aerosol can through 3/4" plywood.

[Technician1002]

You may wish to do some in barrel launch testing to find the optimum length for your barrel. I found that a 2 inch barrel has some serious flow limitations that reduce the flow considerably if it is very long.

For some ideas, here is a link to some 3 & 4 inch barrel length testing. This is a page I produced.
https://inteltrailblazerschallenge.wiki ... rim+method

Near the bottom of this page is this image showing the time taken to travel the last few feet in the barrel where no accelleration is achieved. A shorter barrel removed the excess air drag in the length and provided better launch speeds.

If you can, try capturing your launch data. We put a t shirt through a double layer of wall to wall carpet.


If you don't have a scope, Audacity works fine for measuing the launch data.

[wdr0]

Yeah, I am going to have to look into doing more exact testing of performance. I am sort of new to the whole thing, this is my first cannon. I ended up with a fifteen foot barrel, as that was the longest I figured I could strap on top of the car. The idea being the cannon would be semi portable. I went with the longest knowing I could always shorten it. Right now I am working on a frame for it. I am basically just building a steel truss that it will mount to. Steel seemed excessive for a plastic cannon, but what the heck, it won't cost that much and probably will look better. I will get pictures up, right now I have been using all my spare time for construction.

[wdr0]

Here is the cannon mostly done. I will get the few photos of the build I have and some explanations up sometime soon.

[Ianbuckwell]

That looks great, you going to drive round with that on top of your car, maybe its an optical illusion but it looks huge, how big is your car, think you may need a van or trailer

Is this purely pneumatic?

[wdr0]

No, you are not deceived. The truss is 1ftx2ftx16ft. It is two 8ft sections that bolt together. The tank is two 7ft sections of 4" pipe that join with a union, and the barrel is one 15' piece of 2". I can get all the pipe parts in and on my car. I moved the truss with a freind's truck. It is all pneumatic. Recently tested up the rated 300 psi successfully. I want to get more info up for you guys but have been really busy. Shot a trailer hitch ball 400+ft. Found a skid mark on the ground at that distance, but the ground drips into a valley so I probably won't ever find it.

The dart pictured fired through a fridge top to bottom so all the layers(top of fridge, freezer floor, wire racks, bottom of fridge, and the steel condenser coil on the bottom). It also went through the cinder block set in the fridge, and continued down range. It was getting dark and we could not find any of the three fired. My friend was going to look today in the light. The first dart did not work as planned. The sabot fired, and the dart remained in the barrel. Subsequent rounds were fired with a plastic puck loaded behind them.

[Ianbuckwell]

It is f'ing massive, sorry misunderstood, I had visions of the cars roof being used as a platform for firing it from, looking like some kind of tank!

Must say it looks and performs impressivly. What do you use for your air source as I imagine even with diving bottles you wouldn't get many shots.

[velocity3x]

Here is the cannon mostly done. I will get the few photos of the build I have and some explanations up sometime soon.

I don't see a muzzle brake on the business end of the barrel. Has it occurred to you that the 2" diameter barrel with a large volume of 300 psi air could turn into a "rocket motor" with about 900+ lbs of thrust? How do you hold the cannon in place?

[wdr0]

Well, I did a test at 80 psi on my pick nick table and it only slid back about two feet. The truss is welded steel and weighs at least a hundred pounds. I decided to just fire it(from a safe distance) and see how much it moved and if restraint was neccecary. It dosen't seem to move much at all, all together it does weigh at least 200 pounds though. My air pressure source is a central ac compressor pictured below. It only take about a minute per fill with 120 psi going into the compressor. Works great, but does require a 220 circuit(not exactly readily available in the us). The blue housing on the output is a oil filter, the copper line goes to the tee on the inlet. It's crimped to allow a little flow through so the oil filtered out gets sucked back into the compressor. The filter on the inlet is a plain water separator to keep water out of the oil. I don't have a picture of the piston, will get one, the cannon is semi permanently set up at my friends house 20 minutes south of town.

I may be going out to my freinds house for more testing tomorrow. I will try to get some piston pictures, and possibly even a video. Please feel free to ask away with any questions.

So I did not do anymore testing today. I did recover one projectile(about 200 ft down range after passing through the fridge). I also determined why the cannon would no longer pressurize after our last shot. The piece of inner tube the forms the seal somehow folded under itself on the right.(yes I know, my piston is not pretty, or quality material, but it works). I may soon be working in a machine shop so may have the means to make better such things. I hope to actually get a chance to fire it more tomorrow, and intend to get video.

[wdr0]

So today I was able to do more testing. Fired two of the sabot rounds toward a log. The first impressively embedded itself all the way up to the fins into the log(14+ inches in the log). The second about 7" imbedded, and the 3/4" solid steel shaft bent. Also fired hitch balls at various cans. I did get video, I will get it up sometime but I still have to figure out how as I am new to it.