Community Project Poll

[inonickname]

I'd happily take part in number two if the bore size was reduced. To be honest a large compressor wouldn't run that for long. I have plans drawn for one that use a centrifugal magazine and a timed rotary valve.

[Ragnarok]

I would cut down on the bore size, especially if the air supply is to be self contained, otherwise the "comfortably held" specification becomes difficult to achieve.

Actually, on the note of #2, the desire for something "minigun-esque" was how I originally got into designing the auto hybrid. The demand for both the power and the rate of fire I wanted would have trashed any air supply if doing it purely pneumatically.

By doing it with a hybrid, I could cut back on air supply needed for the same performance by about 80% - similarly cutting back on the flow needed through a regulator.
(It got switched to a single barrel design later, mostly to make synchronisation of parts easier, but partly because it was unnecessary weight and power consumption. However, doing it as a gatling cannon is still entirely possible.)

That's sort of what I'd like to see in this community project - having hard criteria to meet, then finding a lateral way of dealing with the problem.

[deathbyDWV]

I'm thinking for number 1 it could incorperate a stock that is held on both shoulders. It could be made out of pipe and could have a built in recoil reduction system. It would also be cool if we made the piston valve a blow forward bolt.

[jeepkahn]

EDIT: for instance, cannon #1 doesn't have to be comfortable in ragards to recoil. All he was saying is that its a hand held cannon and must be reasonably practical to use while holding. Nothing mounted to a tripod etc. Actually, I think a ridiculous recoil could very well add to the excitment and make videos more entertaining to watch. It will certainly increase the wow factor.

Sorry, but it's no fun when a cannon sends someone to the hospital due to recoil... My nieces bf had 4 stitches installed below his eye because of the decimater, ...If you're feeling froggy I'll make a stock for it and you can shoulder fire it if you like.. It lifts a 30lb+ tripod like its nothing even with my 250lbs leaning into it... And it's only a little 1" bore pneumatic...

I can only imagine a 2" bore 10x hybrid...

[Pookydarts]

For the Girandoni style proposal, pretty much any thing that you see here would suffice:
http://www.youtube.com/watch?v=PgdfMa8caNg

So long as it splits a 2x4 at 50m.

For freedom, take away the requirement to work using a cam, (to allow blowback or other actuation) and for focus (and to try to push us to achieve together something slightly beyond what a single member could achieve individually) let's say something like the one at 52 seconds.

And if semi is more achieveable than full auto, so be it.

[jackssmirkingrevenge]

For the Girandoni style proposal, pretty much any thing that you see here would suffice:

So long as it splits a 2x4 at 50m.

The Caselman is an established design with plans available and anyone with a half decent machine shop and a bit of patience could make it - it would be an achievement but hardly any innovation there.

[Pookydarts]

Bugger.

Thanks for the links though!

[Ragnarok]

I'll make a stock for it and you can shoulder fire it if you like...

Actually, to tell the truth, that might even be a better option.

As I said to Moonbogg in the chat the other day, 2000 grain projectile at 1450 fps, 114 grains of propellant from a 25 lb. 10 oz rifle. That works out at about 139 ft-lbf of recoil. Unpleasant, but clearly controllable.

Your projectiles are slower and lighter, and the Decimator is heavier - in other words, things that will lower recoil energy. As I don't have a value for the Decimator's chamber volume, I can't give you a number for the recoil energy, (I should note however, a vast majority of the recoil you're experiencing will probably be from the gas' momentum. Using a less dense gas than CO₂ would cut the recoil), but I can't see it being so much larger than that.

Of course, if you have decent specs on the Decimator's chamber volume, I could get back to you with an actual number.

Personally, I think the issue here is more that you're choosing a poor method of controlling the recoil (a stock would likely be much better) and a very dense propellant gas.

Anyway, with your muzzle brake (particularly if the blast were directed backwards), you'll probably notice a very dramatic reduction in recoil - omitting gas momentum, the recoil for the 30 lb Decimator firing 1200 fps 1" steel balls is a mere 16 ft-lbf...

[jeepkahn]

Chamber volume=63.617in3
weight=30ish lbs
projectile=956grain
gas=co2@700psi

now that you mention it, shooting from the hip it is relatively managable, but for comparison, from the hip my 12ga shooting slugs kicks less than the decimater...


Also, a note on muzzle brakes, from the research I've done it's not the muzzle blast being directed backwards that supplies the recoil arresting(it plays a part but not significantly), it's the amount of surface area impacted by the high velocity gases(which has a fair amount of inertia)...Basically the weight of the gasses at velocity impact the surface area of the brake pulling the gun forward, the reason for the angle on brakes is to maximize the surface area and angle of impact...

[Ragnarok]

now that you mention it, shooting from the hip it is relatively manageable...

Also, if you're shooting from the hip, you'd find it hard to get hit in the face by the recoil.
I imagine part of the thing is that you're leaning into it, bringing your face closer to the recoiling cannon - while a stock also demands such proximity, the fact it pushes back on the shoulder rather than the hands forces back the torso (and its large mass compared to the hands) and in the process, brings the head with it.

Anyway... 62 gram projectile at 365 m/s (~1200 fps, as your chrony readings tend to say), about 90 grams CO2 (which I'm assuming to have an average velocity at the muzzle of 300 m/s*, probably generous), in a 13.6 kilo cannon... 90 Joules recoil energy, or 67 ft-lbf.
*The fact that this is less than the muzzle velocity isn't a problem.

A lot of recoil, but nothing that a stock and a good stance couldn't handle. Wouldn't be entirely comfortable though, and might well cause "flinching".

But with a good muzzle brake, you could expect that to fall dramatically. Like I say, the gas has momentum of ~27 Ns, and the projectile momentum of ~23 Ns. Compare to the 4 bore, with propellant momentum of ~9 Ns and projectile momentum of ~57 Ns.

You'll find this with a lot of high pressure launchers, that the gas is actually more massive and fast than the projectile that it's propelling (thus being responsible for the majority of the recoil - as can be demonstrated by dry firing). For that reason, muzzle brakes can be more useful on launchers than on rifles.

from the research I've done it's not the muzzle blast being directed backwards that supplies the recoil arresting, it's the amount of surface area impacted by the high velocity gases

Newton's third law... if you want the launcher to experience an acceleration towards the muzzle (i.e slowing it), then the gasses must experience an acceleration towards the breech.
It may not necessarily reverse the direction of the gasses, but it must at least slow them. If it can reverse the flow (i.e. putting a larger impulse on the gases than merely slowing or stopping them), then all the better.

Basically, you want to change the flow speed of as much of the gas as much as you can - so large areas (to affect more of the gas) angled to direct those gasses backwards (to change the speed as much as possible)

[jeepkahn]

I've also often wondered how much of a pneumatics recoil comes from the exhausting of the leftover gases once the projectile leaves the barrel... As you said, the mass of the gas is often larger than the projectiles mass, which leads to the thought that the post projectile gases are traveling significantly faster than the projectile, therefore inducing more rearward thrust than before the projectile exited the barrel...

i.e. the projectile causing a sharp kick, but the gases exert a strong shove after the kick, causing a more dramatic SENSATION of recoil...

[Technician1002]

For freedom, take away the requirement to work using a cam, (to allow blowback or other actuation) and for focus (and to try to push us to achieve together something slightly beyond what a single member could achieve individually) let's say something like the one at 52 seconds.

And if semi is more achievable than full auto, so be it.

Good point. A solenoid with sufficient power could make an electric hammer to operate the valve. ROF and full or semi auto would be a simple switch selection or trigger pull pressure.

[Moonbogg]

Cannon #1 wouldn't cost 2 grand. Not a chance. This insane cannon only cost the guy $700

Like Ragnarok pointed out more than clearly, the cannon can be designed to absorb recoil. Simple a that.

VOTE CANNON #1! SUPERSONIC BASEBALLS!!!

[Ragnarok]

The projectile causing a sharp kick, but the gases exert a strong shove after the kick, causing a more dramatic SENSATION of recoil...

Well, recoil is somewhat hard to figure out completely. "Felt recoil" doesn't always match up to actual recoil energy (energy being far more important than recoil momentum), but it can't be quantified, so for comparison, you have to go with the numbers, not any.

Also, I should dispel the myth of there being an initial "kick" from the projectile, By the time you're feeling the recoil, the projectile is already long gone. Consider, that with the Decimator's 56" long barrel, the launcher has recoiled only about a quarter inch by the projectile is gone, which isn't enough for you to have started to counter it.
Given the fact that the projectile is gone by the time you're starting to slow the cannon and that it's the actual slowing of the launcher/rifle that gives the force of the recoil, you are never directly providing part of the "equal and opposite force" on the projectile.

So, the direct equal and opposite force to the projectile is absorbed by the cannon. The equal and opposite force from you then trying to slow the cannon back to stationary is what you'd call the recoil force.

Thinking that the projectile is still around when you're feeling the kick is a common misconception... false in all but one case - spring air rifles, which consequently demand precision in how they are held so that recoil is as predictable as possible if you still want to get accuracy out of them.

Anyway, that's part of the reason I prefer to work by solely recoil energy (and sometimes considerations of whether a cannon's COG and stock are going to create "straight recoil" or "muzzle climb").

[POLAND_SPUD]

no1 is doable but it seems too simple to be a community project... all you need is a strong chamber, breech load and a muzzle brake

no2 is demanding... too demanding I suppose... does it have to be a Gatling gun ?? could it be specified like 'we're looking for high power full auto gun'?

no3 would be something new when completed ... many people said it would be a cool to build a semi auto/full auto hybrid but it got only 1 vote

For freedom, take away the requirement to work using a cam

it's hard not to agree with that...
no4 and 5 are too specific when it comes to operating principle... IMO it's high time to modify the guidelines for them as they are not interesting for most builders and are so vague that basically any working prototype would be in accordance with the them

why power requirements are mentioned only for no1 (2" and 10x mix) but not for the rest??