Bait Cannon, Help Needed

[baitcannon]

Hey guys, newbie here.....

Long story short, I'm looking to design a bait cannon.

I need some input on where to start in terms of size. I'm looking to build one that will be compressed air, using a spud as the wadding, and needs to be easily portable.

In a nutshell, I go cat fishing and bank fish. No real desire to get a boat and sink money into that, but what I need is to get my bait and line out farther from the bank.

Going to go with a 3" PVC Chamber with a modified irrigation valve to activate it. Going to carry a bike pump that will go up to 160 psi.

Considering the size of my bait. I was thinking a 1"-1.5" diameter barrel.

Length of the barrel is really my dilemma. I would like to keep it around 36" give or take. Air Chamber size (yes I have read the recommended ratios) I figure could be a 1-1 length ratio for keeping it compact.

Now, with this scenario, what kind of distance do you think I could achieve? 100' would be great, if I could get 300', that would be awesome. I'm worried though that the barrel length won't be long enough to achieve this.

Any thoughts or suggestions? Accuracy isn't an issue, just distance.

Thanks for all the help, don't beat me up too bad.......

[jackssmirkingrevenge]

Welcome to the forum!

I highly recommend downloading GGDT: http://www.thehalls-in-bfe.com/GGDT/

It will allow you to play with different parameters such as chamber size and pressure, barrel length etc. to give you an idea of performance and it also comes with a handy external ballistics calculator that will give you an idea of what range is possible.

I assume you are planning something like this, in which case the range is difficult to estimate because of the line drag which is what is the biggest range limiter, but you will at least be able to see which combination of parameters will give you the highest muzzle velocity for a given weight.

[baitcannon]

Thanks for the link to the calculator! That's a huge help in at least getting part way to where I need to be.

I had done the reading on the equations to do the math yourself, but like you said there is going to be many limiting factors. At least with the calculator, I can play around with different design scenarios to see what would possibly work for my needs.

If anyone cares, I will load up photos as I design the cannon.

One other question I have is the that it seems that the piston valve is the best overall valve to use. Has anyone used butterfly valves at all? Seems like you can make one spring loaded and get quick opening action with one.

[Zeus]

Butterfly valves are ostensibly similar to ball valves, so you can enter a generic valve in GGDT, add a 45% flow coefficient and between 50-75ms opening time to model it if you want to try it out. A piston valve is of course ideal though.

[baitcannon]

What is the flow coefficient for a modified sprinkler valve.

Think I'm going to go that route as it seems to the middle of the road between a ball valve and piston operated.

[jackssmirkingrevenge]

One other question I have is the that it seems that the piston valve is the best overall valve to use. Has anyone used butterfly valves at all? Seems like you can make one spring loaded and get quick opening action with one.

Opening a large butterfly valve will require a spring and triggering mechanism of considerable force. It is much easier to allow the air to do the work with an exhaust valve. If you don't feel up to the task of constructing a piston valve a modified sprinkler valve is a reasonable substitute.

[baitcannon]

Right now I'm back and forth on either building a piston valve or just going with the modified sprinkler valve.

Honestly though, I take projects like this and start to over think it. Need to just do the KISS method on the this first build. Simple modified irrigation valve will fit the bill, thought I might be starting to think about building a piston valve. Doesn't look that hard.

Ran the GGDT Calculator, thing I don't get is with a short barrel, with optimization, the reservoir can be pretty small. Only issue is thought the muzzle velocity and speed seems to suffer.

But, with my initial build idea numbers, my muzzle velocity is good, speed is good, and even with a 2.5 drag coefficient for my odd bait I'm slinging, and 1.5 psi projectile drag in the barrel, I'm looking at approximately 300' for projectile distance, and that's the target I'm looking for.

[jimmy101]

One challenge with opening a ball or butterfly valve fast is how do you stop it? The stronger the spring, the faster it opens, the harder it is to stop, the more likely it is that something breaks.

[baitcannon]

I was thinking with a butterfly valve that you could mount it so that the air pressure from the reservoir will force it open. You would need to make a very strong trigger to hold it closed.

But then you could run into your trigger binding and not wanting to release.

The release on the trigger will be pretty violent also. Not sure how safe that would be.

And it didn't think of the mechanics internally, you are right in that you could run into slamming the thing open and potentially breaking something.

For my first build, just going to do the simple mods to the irrigation valve. Going to keep it simple. Ended up buying some spare PVC peices from a guy on Facebook, basically got them for cheap so I have room to play.

Got a couple of blow guns too. One is an older one that has a no spring and a push button.

[baitcannon]

Ok, so I got all my parts rounded up that I need. Going to do the extra modified irrigation valve.

Got lucky and found a couple of schrader valves with NPT threads. I didn't think they were out there and was trying to figure out how to get one installed on a 1/4 inch brass T to put in the cap of the irrigation valve so that I can fill through the pilot.

Here's a question I have though. To make the piston for the irrigation valve, I came up with large, but thin fender washers. The O-ring I found should work great in the groove I need to make.

Basically it's 4 fender washers stacked on each other. The two center ones I will reduce the diameter to accept the O-Ring.

So does anyone think this is going to be too heavy? Should I bite the bullet and just try and make my disk's out of PVC or some other lighter material?

[jackssmirkingrevenge]

Here's a question I have though. To make the piston for the irrigation valve, I came up with large, but thin fender washers. The O-ring I found should work great in the groove I need to make.

What do you mean? An irrigation valve already has a diaphragm, which is effectively the "piston" so the only modification really is to remove the solenoid pilot and replace it with a higher flow blowgun valve.

[baitcannon]

I am doing Hubb's extended modification of removing the diaphragm and spring and filling the chamber thru the pilot.

I saw it in the pdf file he created and figured I might as well try to achieve optimal air flow without any restrictions.

[jackssmirkingrevenge]

Never heard of this one, do you have a link?

[baitcannon]

Sorry for the delayed response. I started to get the parts together for the cannon, but when I looked at my work bench in the garage, I sighed....Ultimately I spent the better part of 4 days cleaning up my garage.

Now I am helping my son with his livestock at the county fair. (mmmmmm, future bacon...) Should be able to get back to building next week.

This is the thread I picked up the idea. It is a sticky in the pneumatic section.

http://www.spudfiles.com/pneumatic-cann ... 16786.html

The more and more I think about it, I think I will be making the lighter version of the piston. Going to try and do it the right way the first time.

[baitcannon]

Cannon is done!

Test firing at 100 psi yielded a conservative 100 yard shot at a 45* angle.

Needles to say my 9 year old son was ecstatic....

So here is a pic of the final product. As a former landscaper, I had plenty of materials laying around to build it. The PVC pipe was the only thing I didn't have.

Now, I will explain my piston design in the next post. I used Hubb's modified irrigation valve design, but simplified it. I did mess up on one aspect of the design, and I might buy a new valve to correct.