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Mechanical/Spring Powered Cannon

A place to ask general spud cannon related questions.
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Mechanical/Spring Powered Cannon

Unread postAuthor: Dr meat201 » Tue Dec 14, 2010 5:34 pm

Has anyone here seen a good mechanically powered or spring powered cannon? i.e. elastic or springs to store potential energy. My friend and i got to talking today about one that would use a car suspension spring to impart the force on the projectile. On a golfball. Then, we got to talking about the realisim of such a design. Recoil would be massive and it would be impossible to load (compressing it by hand - ouch! ). But, back on topic, has anyone seen such a design?
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Unread postAuthor: jackssmirkingrevenge » Tue Dec 14, 2010 5:58 pm

It's not the best of ideas, if you look at commercial spring rifles one of the most powerful is the Webley Patriot which doesn't exceed 30 ft/lbs, and is about as powerful as you can get before it's impossible to cock.

Pneumatic rifles on the other hand go up to several hundred ft/lbs and are much easier to shoot accurately, unless you have a machine shop and are making it out of mechanical interest, it's best to steer clear of home-made springers.
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Unread postAuthor: Dr meat201 » Tue Dec 14, 2010 6:07 pm

I have made a few pneumatic ones but I was just a little bit curious as far as spring power is concerned. My friend and I thought that perhaps (With some effort on 2 people's parts) the suspension spring from a motorcycle or dirtbike. That is, unless you could devise a way to make a gearing system. That would make it rather easy (if a bit more time consuming) to reload.
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Unread postAuthor: jackssmirkingrevenge » Tue Dec 14, 2010 6:16 pm

You could no doubt make a powerful spring gun, but the equivalent pneumatic with the same power would be incredibly lighter and simpler to manufacture.

Think of how many pumps it takes to fill the chamber of a medium sized pneumatic, a springer has to compress all that air in one go, to achieve the same performance it's going to have to be extremely heavily engineered.

A possible "easy" option for a large compression piston type launcher would be to use gravity, something along these lines, but it would obviously only work as a fixed "siege" type launcher.

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Unread postAuthor: Technician1002 » Tue Dec 14, 2010 6:27 pm

The difficulty in spring power is the springs have mass. Since they have mass, the energy in releasing them is consumed in accelerating them. Unless the spring is the projectile, much of the spring energy must be absorbed back out of the moving spring in a safe fashion after the projectile is ejected.

Ways to reduce the amount of energy consumed by the mass in the spring, it is common to devise ways to have the mass of the spring move much more slowly than the mass of the lighter projectile. Examples of this include bows and arrows, catapults, trebuchets, crossbows, and air springer rifles.

Due to the physics involved, most spring power projectile launches have a fairly low maximum muzzle velocity. A modern piston valve air cannon can easily achieve higher velocity.

In an air cannon, the spring storage medium of air is much lower mass, and is ejected with the projectile.

Here is an air springer demo.

[youtube]http://www.youtube.com/watch?v=LCs2423w4Cw[/youtube]
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Last edited by Technician1002 on Tue Dec 14, 2010 6:44 pm, edited 2 times in total.
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Unread postAuthor: Dr meat201 » Tue Dec 14, 2010 6:35 pm

My impression of how I would build one (ignoring the far more logical and cost effective option of pneumatics) would be to have the spring directly force a "hammer" that pushes the projectile out of the barrel directly. Essentially it would be like a pool cue hitting a billiards ball, with the ball attached to the cue until it pushes off.
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Unread postAuthor: jackssmirkingrevenge » Tue Dec 14, 2010 6:42 pm

Dr meat201 wrote:Essentially it would be like a pool cue hitting a billiards ball, with the ball attached to the cue until it pushes off.


The problem is that the ball then can only go as fast as the cue that's pushing it, and that's a fairly heft cue you're going to have to stop. This is why springers compress air in a piston as opposed to striking the projectiles directly.
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Unread postAuthor: Dr meat201 » Tue Dec 14, 2010 6:49 pm

Ah, i see. Oh well, it was just an idea anyways. I'd guess i'll have to get back to the drawing board for pneumatics them :D
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Unread postAuthor: jackssmirkingrevenge » Tue Dec 14, 2010 7:00 pm

what's the objection to pneumatics though, is there any particular reason why you seem to be reluctant to go that route?

You could always use combustion to power the piston ;)
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Unread postAuthor: D_Hall » Tue Dec 14, 2010 7:32 pm

jackssmirkingrevenge wrote:what's the objection to pneumatics though, is there any particular reason why you seem to be reluctant to go that route?

You could always use combustion to power the piston ;)


Which is how a 2-stage gas gun works.
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Unread postAuthor: Moonbogg » Wed Dec 15, 2010 1:45 am

So the second stage causes super heating and expansion? Couldn't you use a pneumatic piston to slam into the air cavity infront of it to cause superheated air expansion? It could be called the "Pneubustion cannon".
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Unread postAuthor: Technician1002 » Wed Dec 15, 2010 1:44 pm

D_Hall wrote:
jackssmirkingrevenge wrote:You could always use combustion to power the piston ;)


Which is how a 2-stage gas gun works.


It is not in the immediate future. I have a 2 stage in the planning stage. Stage one will be the 8 gallon chamber with a 4 inch valve. The second stage would be a 4 inch piston compressing a volume for a golf ball barrel. I expect to exceed 1,000 PSI in the second stage with compression heating.

The second stage compression ratio should turn out to be about 20:1 to 30:1 or the compression in the Diesel engine.
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