Fishing/Bait launcher Pneumatic cannon

[jackssmirkingrevenge]

Currently I have a 40" barrel. How far from the base should I drill the holes to vent the barrel into the sleeve? Once I get it together I will experiment to see if I need to extend the barrel and the sleeve.

The best place to put the vents is just after the projectile reaches maximum velocity in the barrel. If you put them before, you'll lose performance, if you put them after then the deceleration wont be optimized. This point will of course vary according to weight of projectile, firing pressure etc.

You can see it in this simulation at about 14 inches in a 40 inch barrel, using a much smaller chamber:

Note however that the chamber is much smaller than the on you're using. You really should aim for a small chamber at high pressure as opposed to a large chamber at low pressure, because the latter will not give you good enough acceleration.

For the above example I halved the chamber volume and doubled the pressure, technically the same amount of air - but we increased velocity by 12%:

I really recommend plugging numbers into GGDT (That I don't think we than D_Hall enough for!) before starting construction, it will save a lot of trial and error and wasted PVC.

[Pbbraun]

Attached is my first try with GGDT. What do you think? I use a MAC so I had to dig out an old PC notebook to run the program.

Sorry for the flaky file but I think you can read it. Looks like I the 1/4" holes (vents) 4 of them should be about 25" from the base of the barrel.

Hope you can open the file.

[jackssmirkingrevenge]

Attached is my first try with GGDT. What do you think? I use a MAC so I had to dig out an old PC notebook to run the program.

It's really hard to read the data, can you get a better screenshot?

Looks like I the 1/4" holes (vents) 4 of them should be about 25" from the base of the barrel.

25" looks about right for maximum acceleration assuming the barrel is 40 inches long. You're going to need more vents for efficient braking though. The barrel cross section is 3.1 square inches while 4 x 0.25" vents is 0.2 square inches...

[Pbbraun]

Tested it today. Drilled 4 3/4" holes in the 2" barrel. Put an arrestor on the end. Pumped it to 40#. The lightweight pvc sabot, made from a 1 1/4" end cap (about 2 oz) blew the arrestor off. See pictures.

Don't know where to go now....

Thinking that finding out how to make a biodegradable sabot may be the solution. Any suggestions on how to do that would be appreciated.

[jackssmirkingrevenge]

Did you fire it with an empty sabot? It's critical that is is full because otherwise it Will accelerate much faster and put more stress on the arrestor. In any case as previously stated your chamber is far too big vis a vis the expansion space to be very effective.

That being said, perhaps if you're more concerned with the fishing than spending too much time doing launcher r&d perhaps a biodegradable sabot is the best route. Surely a papier-mâché paste using water, flour and newspaper to press cup shapes would not be too difficult? http://www.ultimatepapermache.com/paper-mache-recipes

[Pbbraun]

You are correct... the sabot was empty. I was thinking about the paper mache idea. Will the paper mache be strong enough to handle around 6 oz of weight/bait/hooks/etc?

I was thinking about using the 1 1/4" pvc as a form for the sabot. Also thinking about replacing the pvc barrel with a stainless or aluminum barrel as the pvc barrel is not smooth on the inside.

You said:"chamber is far too big vis a vis the expansion space to be very effective". Do you mean that the fill chamber is to large for the barrel? Would extending the barrel help?

My current setup does a good job of getting the sabot out a long way.

Thanks for your help.

Bill

[Pbbraun]

One more thought. Would a 1" slice of a potato (2" diameter) work as a piston/sabot to launch the bait with the bait wrapped in wet biodegradable paper?

[jimmy101]

You could use pycrete for a reasonably sturdy, biodegradable sabot. Search Spudfiles and the web. If you use newspaper it is stronger than if you use sawdust. Short lengths of barrel can be used to cast the sabot. The newspaper (or sawdust) greatly reduces the rate of melting. A half dozen or so in a decent cooler should stay frozen all day.

[Pbbraun]

Jimmy,

Thank you for the info. Recently while fishing in Mexico I used squid. Got quite a bit of action but was beat up in the surf. That is why I built my bait launcher. Squid and probably most other effective bait really stink. I know I stunk up the refrigerator in our rental. Problem is that if I freeze bait I am concerned about stinking up the fridge. That is one reason I am trying to develop a sabot that is biodegradable and doesn't need to be frozen. I have not seen any biodegradable sabots on the Internet but I am working with a manufacturer that make biodegradable tubes that may be the solution. If I am successful and the cost is reasonable I may market the tubes. Time will tell. One concern I have is if I just pack the line, sinker, hook, bait into the tube will it get tangled when landing.

I have experienced backlash launching with a spinning rod.... I have purchased an Alvey reel and will be seeing if that works better. Lots of trial and error but it is fun and doesn't break the bank.

I really appreciate everyone's comments/suggestions.

Bill

[jackssmirkingrevenge]

I was thinking about the paper mache idea. Will the paper mache be strong enough to handle around 6 oz of weight/bait/hooks/etc?

With a thick enough base, perhaps reinforced with corrugated cardboard disks, it should be up to the job.

One more thought. Would a 1" slice of a potato (2" diameter) work as a piston/sabot to launch the bait with the bait wrapped in wet biodegradable paper?

That... would probably also do the trick do fish like potatoes? hehe

A stack of cardboard disks cut from a stout box would be a better bet though, you could sharpen a bit of the same pipe you used as a barrel to make a "cookie cutter" tool to make them the right size easily.

You said:"chamber is far too big vis a vis the expansion space to be very effective". Do you mean that the fill chamber is to large for the barrel? Would extending the barrel help?

Yes, the chamber is far too large. If you refer to the simulations I posted like the one below, you'll see that I needed to use a tiny chamber (4 inch length of 2 inch diameter pipe) in order to make it work using air braking:



For your current chamber to work your barrel would need to be much, much longer, too long to be practical.

I really think that for your purposes, a biodegradable sabot is a better solution unless you're willing to invest the time and effort in making an effective captive piston - since you want to travel with it, perhaps the size constraint is not really an obstacle that can be overcome while still having good enough performance.

[Pbbraun]

When you talk about "chamber size" are you talking about the air reservoir (where the air is stored before it is released into the barrel) or the chamber that surrounds the barrel?

Thank you for your continuing help. We are in Galveston Texas this week and I will do some experimenting and post the results.

[jackssmirkingrevenge]

I'm referring to the air reservoir - the bigger it is, the more space the air would need to expand in the barrel sleeve, and at your current size the sleeve would have to be far too large.

Thank you for your continuing help. We are in Galveston Texas this week and I will do some experimenting and post the results.

Don't forget to put a full load in the sabot if you move on with this concept - the more you load it, the slower it will go and the less effort is needed to stop it (assuming whatever is inside the sabot is free to slip out with relatively little friction).

[Pbbraun]

Progress. Had fun in Galveston. Tried out the launcher and it worked well. Made some changes upon our return. Replaced the sprinkler valve with a 1" brass valve. The sprinkler valve has a tendency to leak if any particles enter the valve. The brass valve works just fine by simply hitting the handle to open it. I tried a PVC valve at HD but it is stiff and hard to open quickly. Did use 2" diameter, 1" thick cut potatoes as a sabot of sort. Worked well. I am going to try to manufacture paper mache sabots as a biodegradable alternative to the potato. They would fully enclose the bait package.

I replaced the PVC barrel with a schedule 40 2" ID aluminum barrel. Got it threaded at ACE hardware ($2.50).
HD was not enthused about helping me.

incorporated a PVC stand and rod holder. Used 2" PVC Snap Tee ordered from FlexPVC. That will slide over the 2" barrel. Can't use a 2" Tee as there are stops that don't allow it to slide down the barrel.

[jackssmirkingrevenge]

Basic but it works

The brass valve works just fine by simply hitting the handle to open it.

There are ways of spring loading it for more consistent performance. Also, consider mounting the ball valve at the end of the barrel to reduce dead space and increase performance even more.

HD was not enthused about helping me.

Boooo, what squares!