A crossbow pneumatic idea

[boyntonstu]

http://www.airowgun.com/pellet.php

I spoke with the company.

The guy said that a 70 pound pull would shoot a .22 pellet about 600 FPS.

The idea is simple; the bow forces a piston down a "bicycle" type pump which is the compressed air source.


HMMN!


Why not use an 80-85 pound self cocking crossbow pistol as the basis for a homemade air gun?

see:

Imagine a .375 piston 6" long.

The 80 pounds on a .375" diameter (0.110 square inches) would create 727 PSI

I am not sure of the volume that the .375" diameter would generate but let's guess a 6" stroke.

6" x .11 = .66 cu-in.

A .22 barrel with an equal volume of .66 cu-in would be about 17" long.

OTOH A 150 pound crossbow rifle could push a much larger diameter piston about 24".

For the same .37" diameter this crossbow would yield 2.64 cu-in at about 1,400 PSI!

Comments most welcome.

BoyntonStu

[THUNDERLORD]

Yeah, JSR linked to that one about 1 million years ago, and it was discussed before.
(I Had it in my "favorites" before that).
But, New info/more discussion on it is cool IMO.

It's been the opinion of myself and other members that it's not "optimized" for optimal power as it could be.

Unless someone is an "archery freak", another spring besides a crossbow or bow (like an automotive coil spring) seems more practical.
Although it would be cool to see an automotive "leaf spring" suspension converted into similar IMO.

Thanks for the mathematical info, I will check it out sometime soon.
Got to go pick up my lady...sucks being apart during week...d*mn economy...maybe I'll come up with the best design ever and...
The world will be mine (/fellow spudders)!!!...MuHahahaMu HAhaHAha ah ah ah!!!
BTW, (I am thinking of a jet pack w/ nozzle into giant vortex maybe). 8)

[TurboSuper]

I reckon you'd need something to hold the BB back in order to generate any significant pressure.

[Technician1002]

Getting the transfer of energy correct is rocket science. Potential energy is released to kinetic energy of the piston, string, etc. The mechanical energy at the same time is converting back to potential energy as compressed air, which at the same time is being converted to kinetic energy on the projectile.

The balancing act is to get everything to come to a stop with all the energy transferred to the projectile with no energy returned back upstream as recoil.

It should be able to work, but the timing, distance, volume, mass, energy, would make my head spin.

[boyntonstu]

I reckon you'd need something to hold the BB back in order to generate any significant pressure.

Did you see the video?

.22 at 600fps.

Whatever they do, it seems to work OK.

How about a multiple rubber 'slingshot' gun instead of a bow?

5 slingshots should produce a few hundred pounds of pounds of force over 24-30" of throw.

BoyntonStu

[jackssmirkingrevenge]

Here's one I made earlier

[john bunsenburner]

Well, I would presume there is easier ways of doing it, cheaper too. But if you get the math right and can machine parts in the correct sizes id say give it a go.
The only recommendation i have is to make the bow your self from either glass fiber or carbon fiber if you have the tools already, that would make it cheaper and more like what you want. Perhaps one could eliminate a few steps by having the projectile directly in front of the piston so that the piston accelerates it, instead of having air pressure build up first. Otherwise this calls for a burst disc...

If you do it make it bit with a stand and perhaps a lever for cocking, and be sure to make a nice reloading mech for it, especially for the burst discs if you use them.

[boyntonstu]

I thought of using a pressure relief valve.

You draw the bow and it pushes the piston down a cylinder.

There is a pressure relief valve set to open when it reaches say 1,000 PSI.

IOW The projectile is immobile until the desired pressure is achieved.

An additional chamber and a check valve could also be considered for multiple 'pumps'.


BoyntonStu

[Brian the brain]

With the recent discussion of autoignition or " dieseling" airguns...I think this topic deserves a revisit.

I made a marble shooting rubber band gun once ( about 14 years ago I believe, that would be perfect for this.

Basically a harpoon type gun, with a toprail to guide the marbles, much like a barrel would do.

It had about 90 kilo's of pull..and shot a marble halfway into solid wood.

I'm guessing that would be enough force to get a piston to diesel...
Over under type...flip it around to get it to be more compact...with the action in front...and the piston popping towards the back...hmmmm
Cocking it with my full weight...

Yeah...I see a new project coming up...

[TurboSuper]

I'm thinking it works on Venturi's principle in that it uses the pressure generated in the cylinder to create a high velocity airflow in the barrel. Just a thought.

[boyntonstu]

With the recent discussion of autoignition or " dieseling" airguns...I think this topic deserves a revisit.

I made a marble shooting rubber band gun once ( about 14 years ago I believe, that would be perfect for this.

Basically a harpoon type gun, with a toprail to guide the marbles, much like a barrel would do.

It had about 90 kilo's of pull..and shot a marble halfway into solid wood.

I'm guessing that would be enough force to get a piston to diesel...
Over under type...flip it around to get it to be more compact...with the action in front...and the piston popping towards the back...hmmmm
Cocking it with my full weight...

Yeah...I see a new project coming up...

I love it!


Thinking outside the box.


BoyntonStu

[mobile chernobyl]

Not to rain on your parade, but wouldn't the power generated by a bow be used most efficiently directly... as in pushing an arrow/bolt projectile?

It's almost like using an air cylinder to push another air cylinder connected to a barrel... your going to lose efficiency through drag in the seals, heat, etc...

It's a cool Idea and all, and a good one for "portability" but it almost seems like just a way to create unnecessary energy losses in the system.

However if your intent was portability and I missed that - Carry on...

[boyntonstu]

Not to rain on your parade, but wouldn't the power generated by a bow be used most efficiently directly... as in pushing an arrow/bolt projectile?

It's almost like using an air cylinder to push another air cylinder connected to a barrel... your going to lose efficiency through drag in the seals, heat, etc...

It's a cool Idea and all, and a good one for "portability" but it almost seems like just a way to create unnecessary energy losses in the system.

However if your intent was portability and I missed that - Carry on...

Have you viewed the Airowgun video?

1 pull of a 60 pound bow and a .22 pellet goes 600 fps.


Is that efficient?

Can you guess what a 150 lb (or higher) crossbow could do with th same technology?



BoyntonStu

[mobile chernobyl]

Yes it appears efficient without looking much further into it, but you must agree - there WILL be losses to seal drag and heat.

I guess what your getting at here is it's portability? In that sense yes, having a 600 fps 22 cal projectile by your side and being able to wind it up (if it's a cross bow) or just pull it back (compound/conventional bow) is nice.

However a break action pellet gun uses a very similar method of storing energy, and is already designed around shooting a pellet, not adapted around a bow system.

It's a cool idea, but certainly nothing revolutionary.

[MountainousDew]

Definitely not revolutionary, because all this would be is a uber boosted nerf gun... But still awesome!