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recoil support

A place to ask general spud cannon related questions.
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recoil support

Unread postAuthor: SpudFarm » Mon Sep 08, 2008 3:47 pm

well simple question put difficult:

whan dealing with loads of recoil, does the chamber generate some of the recoil or just the part of the barrel that has the projectile in it?

i am planning to support the hybrid on only the barrel on my bipod and wonders if it is going to treat normally so the chamber does not tear my bad brass union.

thanks!
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Unread postAuthor: ALIHISGREAT » Mon Sep 08, 2008 3:53 pm

the projectile and gases are whats making the recoil (every force has an equal opposite - thats why a light person will struggle to push a phat person) so the whole gun will recoil backwards...

on another note, every thought of using a muzzle brake?
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Unread postAuthor: SpudFarm » Mon Sep 08, 2008 3:56 pm

haha, my diagram has a HUUUGE muzzle brake on it... :D

so what you say is that if you mount the barrel 100% still the chamber will pull on the barrel, or will the barrel push the chamber?
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Unread postAuthor: man_o_brass » Mon Sep 08, 2008 3:57 pm

That's a simple question of Newton's 3rd Law. The gun pushes a projectile in a straight line down the barrel. The reaction force, therefore will be on the same line in the opposite direction. Whatever bend or fitting is directly behind the barrel will bear the brunt of the recoil force and transmit it to the rest of the gun. In a standard combustion gun, this component in the chamber's endcap, but in pneumatics, it depends on how you've built the gun.

Edit: For clarification, the barrel itself generates no recoil at all since it doesn't push on the projectile. Any friction between the barrel and the projectile will actually pull the barrel forward along with the spud.
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Unread postAuthor: ALIHISGREAT » Mon Sep 08, 2008 3:59 pm

ermm, well i guess the chamber may shoot off :D (but only on you have a weak fitting) i need a diagram :? i don't quite understand what you are getting at?
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Unread postAuthor: man_o_brass » Mon Sep 08, 2008 4:08 pm

I'll put it this way. If you looked down the barrel. whatever part you saw at the other end is the only part that will be pushed on by recoil. That one part will then pull the rest of the gun back with it.

There can be other forces created by gas turning corners in angled fittings, but they aren't much more substantial than the stress of holding the pressure in the first place.
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Unread postAuthor: Ragnarok » Mon Sep 08, 2008 4:13 pm

Ok, this may be a little hard to explain.

In the strictest of terms, as Man o brass says, the force that creates the recoil is just applied to whatever area sits behind the back of the barrel. However, that does not mean only the barrel should be supported, because that only happens on a scale of milliseconds.

When the launcher recoils, you should not think of it as you're providing the equal and opposite force for the projectile's acceleration. The launcher has already done that, and is now moving backwards at a moderate-ish pace, usually a couple of metres a second.
What you're now doing is providing the equal and opposite force to slow the launcher down to a standstill again.

You should really consider the momentum transfer like this:
Projectile, pushes on --> Launcher, which pushes on --> You.

(In Soviet Russia, launcher pushes on you!)

So, in the simplest terms, during recoil, the entire launcher is moving backwards at you, so you should work around that assumption.
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Unread postAuthor: ALIHISGREAT » Mon Sep 08, 2008 4:33 pm

so i was right about the whole gun recoiling :D

so what you say is that if you mount the barrel 100% still the chamber will pull on the barrel


essentially, yes! because the whole gun is moving backwards

if the gun is only anchored to the ground with the barrel, the chamber will still want to recoil backwards, so its the brass union holding the chamber onto the barrel!

so supporting the chamber at the rear is a much better idea as no fittings on the main body of the cannon will be strained!
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Unread postAuthor: Ragnarok » Mon Sep 08, 2008 4:42 pm

ALIHISGREAT wrote:now as for the only supporting the barrel thing

It is worth pointing out that during the projectile/launcher recoil interaction, there are forces from the barrel which will act through these unions in the opposite direction to during the launcher/person recoil, so you could get away with only supporting the barrel.

But personally, I'd avoid such a thing. I'd tie the barrel and chamber together as well as possible, and then control the recoil by slowing both chamber and barrel together.
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Unread postAuthor: SpudFarm » Mon Sep 08, 2008 4:55 pm

i guess i will have to spoil it then..

look at the diagram while reading this:
the gun is only mounted to the bipod on the barrel (hose clams), on the chamber side (everything that is not mounted is) chamber, 2" brass nipple, 2" steel copuling, 2" by 8" steel pipe nipple and 2" female x female brass union. i does this because when i am changing disk the chamber can rest on the wood under it so no lifting/dragging is needed that can damage gauges and stuff.
it WILL kill me if it loosen.

(note, i will only hold it with projectiles under 140grams)
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Unread postAuthor: Ragnarok » Mon Sep 08, 2008 5:09 pm

SpudFarm wrote:look at the diagram while reading this

Exactly how am I meant to achieve that?

I can't read the writing if I'm looking at something else!!! :P
It's impossible to do simultaneously! :D

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Hmm, I can see your reasoning behind the idea, although I wouldn't be too happy doing it myself.
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Unread postAuthor: man_o_brass » Mon Sep 08, 2008 5:37 pm

(sigh)

Like i said, if your design is linear as the picture shows, the endcap of the CHAMBER will experience the recoil. With the barrel clamped, EVERY fitting of the gun will be subjected to EVERY bit of recoil force. If your goal is to avoid stressing these parts, clamp the chamber down and take the barrel off to change disks. You'll probably want to screw a block down behind the chamber as well so that you're not relying solely on hose clamps.
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Unread postAuthor: clide » Mon Sep 08, 2008 7:44 pm

The recoil force comes from the pressure acting on more surface area in the backward direction than in the forward direction. This means that if you plugged the barrel of your gun and pressurized it to your operating pressure, the joints would have about same amount of force trying to pull them apart as when the gun is recoiling if you braced from the barrel. So basically if your gun is safely designed and has all parts operating below their pressure rating it should be able to take being braced from the barrel.

As Rag mentioned you not only have to be concerned about the forces from the recoil, but the forces from stopping the recoil. How much force is generated at that point depends on how fast you stop it. One nice thing about bracing from the barrel is that all your joints are in tension as you are stopping the gun. Fittings are designed to be exposed to tension, but compression is a little abnormal for them. If you brace from the chamber then your joints will be in compression as you are stopping the recoil. This can lead to a sort of buckling action if you aren't careful which could easily snap a fitting.

Normally I would say bracing from the barrel would be best, but since you are standing directly behind the launcher it creates quite a big safety concern with having an unbraced chamber. So in this case I would say brace the chamber and create a setup in the front that confines the barrel and prevents it from moving side to side or up and down, but allows you to slide it forward for loading. You could even put a stop on the barrel that would allow it to slide forward, but once the barrel is all the way back it is braced against your stand. I can draw a quick picture if you're not quite sure what I'm trying to explain.
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Unread postAuthor: SpudFarm » Tue Sep 09, 2008 2:58 pm

hi clide, i does understand what you are trying to say.

but i think i got a idea that can help safety..

a steel plate bolted TIGHTLY to the 2 x 4" under the back of the chamber then have square steel welded in an angle upwards and backwards from the plate so it stopps in the height of the highest point of the chamber and then have a 1/2" plate welded there again (diagram LOOK FIRST THEN READ A BIT AND LOOK AND REPEAT!!)
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Unread postAuthor: jrrdw » Tue Sep 09, 2008 3:08 pm

I myself would be more worried about the soft metal unions (brass) then the recoil. How many shots have you gotten off so far?
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