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Need some help with my design

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Need some help with my design

Unread postAuthor: Hyudryu » Thu Oct 02, 2014 9:22 pm

Hi guys, I have my design for an air cannon, but I have some questions about some parts.

So the concept of the air cannon would be pretty simple. I bought a small bike pump rated at 90 PSI, and I plan on connecting that to an air reservoir (preferably brass or PVC), and connecting the reservoir to a release valve which leads to the beginning of my barrel. My design would look something similar to this
Image

Where the bottom is my bike pump, and the gray section is my air reservoir, the gold section is my brass valve which I found here: http://www.ebay.com/itm/291039822902?_t ... EBIDX%3AIT
And the red part is going to be tube/hose but I'm not sure how to use it. Should I connect the hose to a fitting of some type?


Now after buying the pump, I noticed that the head is threaded, and is made of either polycarbonate/ABS plastic, and is like the diameter of a dime. Now I don't know what to buy that would thread onto it, and at the same time be able to connect to the rubber hose i plan on getting. If anyone knows what that's called, or have any previous experience with a project like this, could you please give me some advice :D Thanks
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Re: Need some help with my design

Unread postAuthor: lockmanslammin » Fri Oct 03, 2014 12:32 am

hi, Hyudryu

I think I understand what you're idea is here... What do you plan on using as a projectile and what are your performance goals?

The basic plan makes sense, but there are some serious upgrades that could be had here. I am currently building an on-board pump pneumatic so I could help you out a bit.

Let us know barrel diameter, and intended projectile, and we might be able to get you headed in the right direction.

Chris
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Re: Need some help with my design

Unread postAuthor: Hyudryu » Fri Oct 03, 2014 3:26 am

Hey Chris,

So the inner diameter of the PVC pipe is 3/4 inch, and my friend gave me these cardboard tubes which are 3/4 inch outer diameter and it fits pretty nicely, and is pretty air tight, but can move freely without much friction I plan on filling the tubes with some aluminum foil or some airsoft BBs along with epoxy to add weight so it will go relatively straight.

As for my performance goals, I honestly don't know how well 90PSI would do. I'd be satisfied if it worked at all honestly. Even if it just barely shoots across my backyard.

So I thought about the design a bit more and my only problem is getting the air to the reservoir. I measured the head of the bike pump and it came out to be 18mm, and I plan on getting a brass fitting tomorrow from home depot, but I have no clue how to mount a hose onto it. What I had in mind was those hoses that are rubber with the outside weaved with some sort of fiber, like modt bike pumps have. I don't know much about those so I'm not too sure how I would connect it together.

Mark
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Re: Need some help with my design

Unread postAuthor: lockmanslammin » Fri Oct 03, 2014 11:37 am

A few things.

First off you can have all sorts of fun with 90psi. All you need to do is efficiently transfer your chamber volume to your barrel, and unfortunately the valve you posted won't do that. Depends on how involved you want to get, but the easiest thing would be a 3/4" ball valve. Beyond that you have diy piston qev's and sprinkler valves. The piston qev can be cheap, but is harder to pull off than a ball valve. The problem with the valve you posted is that it will transfer the air far too slowly. By the time even a small portion of the air is out of the chamber the projectile will have exited the barrell at a slow speed.

Ammo could be as simple as little potato chunks. You just need to sharpen the end of the barrel on the outside, then pound the potato in and it will cut itself to be a perfect fit. Or c batterries will fit. Or you could make a sabbot (google sabbot) and then drop anything that will fit on top of it.

Also you should look through the pneumatic cannon database for a lot of ideas. There are a lot of cannons in there that you could learn from.


It might be simpler to start with if you keep the pump and cannon separate at first. You just need a Schrader valve to screw into the chamber. Make all your connections where the pvc is double thick at the joints.

I could go on and on, but do you have any questions about what I have already said?

One more quick thing, little tubes are ok for filling the chamber, but the path from the chamber to the barrel should have no parts that have a smaller diameter than the barrel.

Chris
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Last edited by jrrdw on Sat Oct 04, 2014 7:43 am, edited 1 time in total.
Reason: Double posting.
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Re: Need some help with my design

Unread postAuthor: Hyudryu » Fri Oct 03, 2014 2:06 pm

I understand pretty much what you are saying, but i'm not sure how to route the air from the chamber to the barrel. I have decided to use the sprinkler valve trigger because it seems pretty easy to make, but how would I connect the hosing from my chamber to the sprinkler? What kinds of adapters/fittings would I need for it to connect? I might use a hose that is like 3/4 inch in inner diameter so it doesn't restrict much airflow, but what material for the hose, and how to connect it is what I'm having problem with.

Mark
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Re: Need some help with my design

Unread postAuthor: lockmanslammin » Fri Oct 03, 2014 7:52 pm

Looking at your drawing what I'm thinking is that you have the but stock are already there. You could have that as your pressure chamber and make it dual purpose. Then there would be no tubing in the crucial area. You would just put threaded adapters on both halves and the sprinkler valve would be the connection between the two. Whatcha think?

If you like the look of the chamber where it is you could still put it there and use it as an ammo holder.

Now you have to look into a pilot valve for your sprinkler valve. A lot of people use a blow gun, or you could use a small ball valve. Either would work, the blow gun just makes it a little handier and more like a normal trigger.

You could also put a battery pack in the mock chamber and actuate it electrically with a momentary button.

I think you will be impressed with 90psi when you get it done. It will be a bit dangerous if you get it working correctly so be careful.

Anybody else have any input on this?

Chris
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Re: Need some help with my design

Unread postAuthor: Hyudryu » Tue Oct 21, 2014 4:14 am

Hey Chris,

I took your advice and made the stock into the pressure chamber, and used the sprinkler valve as the trigger. The cannon fires perfectly and I am very happy :) And now I want to make another one with a larger barrel so I can shoot larger projectiles. I don't plan on making the pressure chamber extremely big, so I decided to just increase the pressure for my next project.

Anyways, for my next project, I got a bigger bike pump, (advertised up to 300PSI) and I was wondering if you can give me some input on that. My PVC pipes claim that they are capable of holding up to 480 PSI at 73 degrees fahrenheit, but the end caps and the elbows i'm not too sure. Also, the sprinkler valve is only rated at 150 PSI max, so what is your advice on this? Should I switch to copper/steel instead of PVC? And if I do so, what should I use for my trigger mechanism?

Thanks,
Mark
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Re: Need some help with my design

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Re: Need some help with my design

Unread postAuthor: lockmanslammin » Wed Oct 22, 2014 11:41 am

I'm glad it worked out for you. You should post some pics of it and give some performance details.

Pvc is rated for water pressure, not necessarily air pressure. Water isn't compressable like air, so if pvc fails with water it just cracks and the water runs out. With air, it explodes and can send shrapnel in multiple directions. There are endless threads on here about this very subject.

I wouldn't get near pvc with 300psi. Especially if you plan on being anywhere near the cannon when it is under pressure.

pneumatic-cannons/topic13286.html

There is a thread about my only higher pressure pneumatic. It is all type L copper with soldered joints and brass threaded fittings. When it was done I pumped it a ways over my intended pressure remotely (around the corner of my garage wall) before I ever got near it while pressurized.

Just trying to point out that there is a level of danger involved here, and that all precautions should be taken.

What kind of size are you thinking of going to? If you stayed with pvc (all pressure rated ) and your old pump you could try a big coaxial with a piston valve.

Higher psi can take a lot of pumping with a bigger chamber, what kind of pump did you get?

I'm not sure if that link will work or if you'll have to copy and paste it to a browser tab.

Chris

Also...

Just to point out what 300psi can do, here is a couple damage photos from that copper cannon I posted. This is what something as light and whimpy as a marshmallow can do at pressure like that. This is a piece of 2x4 and a piece of 1/8" tempered hardboard.

Image

Image

300psi is a lot, and definately out of the toy cannon category. Just be careful and stay safe.

Chris
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Re: Need some help with my design

Unread postAuthor: Hyudryu » Thu Oct 23, 2014 4:30 am

I'll take and upload some pictures of my finished product tomorrow :)
And damn, the last thing I'd want is to have the pvc explode while i'm pumping it. I'm going to try wrapping the pressure chamber with duct tape to try to prevent it from exploding if it does give out, I used 1 1/4" schedule 40 PVC pipe for the pressure chamber, and the pipe is rated 330PSI and so are the elbows and end caps. I'm probably not going to be going past 200 PSI at all with PVC. But honestly I think my sprinkler valve would be the first thing to malfunction if I do exceed the pressure rating, because while the PVC pipes are rated at 300+ PSI, the orbit 3/4" sprinkler valve is only rated at 150PSI. But I will take some precautions when pumping up the rifle. My barrel is 3/4" and I bought a 3/4" diameter aluminum rod on amazon and i'm going to saw it into 3/4" inch projectiles.

I'll upload some performance videos when I get my aluminum rod, and i'll also compare it to my cardboard projectiles.

I got my 300 PSI pump from Amazon. http://www.amazon.com/gp/product/B00FE0 ... UTF8&psc=1 I am honestly skeptical about the whole 300 PSI rating given by the manufacturer, but it at least has the female schrader valve connector so I wouldn't have to press on the pump while pumping.

Also, one thing I encountered is the accuracy of my projectiles. When I shoot from a range of over 15 feet, it would curve to some random direction. Do you have any advice on making it more accurate? Without rifling, this air cannon is more like an air musket haha
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Re: Need some help with my design

Unread postAuthor: lockmanslammin » Thu Oct 23, 2014 5:34 pm

That pump will work, but I think you will be suprised by how many pumps it will take to get the pressure up very high.

What is the length of your pressure chamber?

I suppose the risk you are willing to accept is up to you as far as pressure and pvc go. I would still do an over pressure test with a guard of some sort between you and the cannon and make sure it is safe, and then stay a ways below that tested limit afterwards, but that isn't accounting for colder temps or fractures due to accidental bumps or drops. Just sayin'.

The ID of your barrel is .804, so you will need to patch your aluminum slug with a few layers of t-shirt material or something like that to get a decent seal, and it also may protect the barrel from the aluminum.

Smoothbore barrels are always going to suffer from accuracy issues. My copper cannon isn't very accurate either. Another thing that hurts accuracy is the air that puffs out of the end of the barrel after the projectile exits, blowing it around, you might experiment with an air stripper. It is an extension of the barrel with large holes drilled all over it so the excess air can escape while the projectile is held on course. Another thing is ammo choice. Something that is directionally stabalised might help, such as a dart or something with a hollow back kind of like a standard pellet. I haven't tried much in that regard, maybe someone who has will chime in.
also you should Google airsoft hop-up, you might find that interesting as far as accuracy goes I would assume it would help.

Chris
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