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Simulated recoil on heavy cannons

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Simulated recoil on heavy cannons

Unread postAuthor: Sear » Sun Feb 04, 2018 12:47 pm

Hi all

I'm trying to find the easiest and the most elegant way of how to simulate recoil on heavy cannons.

Existing setup
A cannon with breech assembly and a barrel weighting 45 kg. Steel air chamber and a solenoid valve. Operating pressure is 12-16 bar (can vary within these values in practise). Shot weight is negligible.

Design aim
Now I want this setup to move backwards 30 cm and back rather aggressively when the trigger is pressed. And shoot at the same time.

Solution
For sure a pneumatic cylinder needs to be utilized. I'm trying to think of an elegant solution with minimal number of components. The build-up space is of course limited. Ideally I'd like to have one air chamber, one valve and one cylinder :D
On the serious note, I may need to let someone to design a customized pneumatic cylinder, so existing models won't be a limitation.
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Re: Simulated recoil on heavy cannons

Unread postAuthor: Zeus » Sun Feb 04, 2018 4:26 pm

I don't think you'd need to bother with a custom cylinder. You could consider tapping air from the barrel, or just using a second solenoid attached to the chamber. Fire both in unison. However, make sure you have a satisfactory buffer.
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Re: Simulated recoil on heavy cannons

Unread postAuthor: Ragnarok » Sun Feb 04, 2018 4:44 pm

Faking recoil with a pneumatic cylinder is one of those things that doesn't work all that well (particularly with such a heavy cannon).

True recoil is a very sharp impulse, with all the acceleration happening over a distance of just a few millimetres and then everything after that being deceleration.
A pneumatic cylinder does mostly the opposite - a long acceleration and a short deceleration - and while you can theoretically use generous pressures and small volumes to make it a sharper effect, unless the carriage it's pushing against is very heavy, firmly fixed or both, doing that makes the deception pretty obvious.

Sear wrote:A cannon with breech assembly and a barrel weighting 45 kg. Steel air chamber and a solenoid valve. Operating pressure is 12-16 bar (can vary within these values in practise). Shot weight is negligible.

Why do you have such a heavy launcher for pressures that aren't all that high and an (allegedly) negligible projectile weight?
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Re: Simulated recoil on heavy cannons

Unread postAuthor: Zeus » Sun Feb 04, 2018 4:59 pm

Rag, that entirely depends on whether you want true recoil, or the appearance of recoil to the less educated viewer. You aren't gonna achieve true recoil without a heavy projectile, but for the rule of cool, I daresay a cylinder would be satisfactory.

The alternate option is making your projectile heavier, by using something easily dispersed, flour in a paper wad, etc. But then you're tossing 2kg of flour a shot and making a godawful mess.

Maybe a second cannon below it that fires water :P
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Re: Simulated recoil on heavy cannons

Unread postAuthor: Ragnarok » Sun Feb 04, 2018 5:07 pm

There's still a minimum standard for faking it.

Even the less conversant are likely to spot that something is off if the carriage suddenly lurches forwards under "heavy recoil".
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Re: Simulated recoil on heavy cannons

Unread postAuthor: hectmarr » Sun Feb 04, 2018 7:27 pm

It would be possible not to fix the set of the firing gun - air chamber to its base. Instead, fix it on a rail, or two, so that you can slide the distance you want. With a little expelled mass could be achieved a movement, the whole and leave the base solid. It's just an idea.
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Re: Simulated recoil on heavy cannons

Unread postAuthor: Sear » Mon Feb 05, 2018 4:33 am

Thanks guys! The launcher is so heavy and made of steel only for realistic look and feel. And I'm afraid I can't make the shot heavier even in the form of extra dispensable flour. These parameters are constants limiting the amount of remaining options.

That being said, Ragnarok is right about the minimal faking standard for recoil. The question is whether the initial momentum could not be helped with something (and if this is really needed for cylinder of suitable power)? From what I saw (and I admit this tech is new for me), cylinders didn't seem to have any perceivable acceleration time in the beginning.
Later today I try to put my current idea of solution into a simple graphics.
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Re: Simulated recoil on heavy cannons

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Re: Simulated recoil on heavy cannons

Unread postAuthor: Sear » Mon Feb 05, 2018 2:14 pm

Here is my simple drawing. What I have in mind is a modified pneumatic cylinder with an exhaust. Upon opening the valve the cylinder pushes the barrel-breech assembly backwards for a moment. Then the piston reaches the exhaust and the air rushes to the barrel to make the shot. Piston then travels further with smaller amount of remaining pressure; mainly because of already created momentum of the barrel and the breech assembly.

What I tried to achieve with this solution is that only a single valve and single air chamber could be used. And to create a compromise between the power applied on a piston and an inevitable delay of the shot.
The same could probably be achieved with a specific 3-way solenoid valve but likely with greater space demands and with some controller circuit necessary.
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Re: Simulated recoil on heavy cannons

Unread postAuthor: Ragnarok » Mon Feb 05, 2018 3:14 pm

Sear wrote:From what I saw (and I admit this tech is new for me), cylinders didn't seem to have any perceivable acceleration time in the beginning.

If they're trying to shove a 45kg launcher about, they are going to be slowed down quite a bit.

Then the piston reaches the exhaust and the air rushes to the barrel to make the shot.

This flow restriction is going to *massively* cripple performance.

You'd be far better off doing it the other way around, tapping gas off the barrel for the pneumatic cylinder (rather than tapping gas off the cylinder for the barrel).
If you trap some gas in the cylinder with something like a check valve and a way of venting it once it'd recoiled enough, then it'd let it recoil for longer than the projectile was in the barrel.
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Re: Simulated recoil on heavy cannons

Unread postAuthor: Sear » Mon Feb 05, 2018 4:03 pm

Just to make sure I got it correctly, Ragnarok: by tapping gas off the barrel you mean to put something like a T-piece in the hose that currently leads the air into the barrel and connect in to the cylinder? Or something more elaborate? The air discharge is very quick but the cylinder needs the pressure to be applied for some time in order to do its job.
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Re: Simulated recoil on heavy cannons

Unread postAuthor: Ragnarok » Mon Feb 05, 2018 4:17 pm

Sear wrote:Just to make sure I got it correctly, Ragnarok: by tapping gas off the barrel you mean to put something like a T-piece in the hose that currently leads the air into the barrel and connect in to the cylinder?

Not exactly, because that's not how I was expecting the launcher to be laid out.

It would help if you could provide some pictures, I think.
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Re: Simulated recoil on heavy cannons

Unread postAuthor: Sear » Mon Feb 05, 2018 4:56 pm

Ok, here is how the setup looks like.
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Re: Simulated recoil on heavy cannons

Unread postAuthor: Ragnarok » Mon Feb 05, 2018 5:17 pm

... right, I've gone back and looked through your posts.

If this is for paintball, the performance of the design is probably not a major concern.

I do have two concerns though:
-If such a light projectile and low velocity is involved, the pressure and the time the system is under pressure simply may not be enough to be able to drive a recoil mechanism off the same valve.

- And I do question the safety aspect of having a 45kg launcher recoiling "aggressively" in the relatively hectic environment of a paintball game. If anyone is the slightest careless or a component fails at the wrong time, someone could get fingers broken or severed.

I'm reminded of this:
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Re: Simulated recoil on heavy cannons

Unread postAuthor: Sear » Mon Feb 05, 2018 5:34 pm

The performance itself may not be that big of a trouble, but as you mentioned before the effect has to be at least somewhat believable.

Regarding your concerns:
- the system is under pressure for a brief moment only (and it is not exactly air tight in the breech area either). That's why I wanted the air to go to cylinder first. Yet I can safely raise the pressure up to 40 bar if needed (but I cannot let it in the barrel at once else the projectile reaches unsafe velocities quickly).
- that part could be mitigated by physical restrains that protected the gunner from sticking parts of the body in the way of the recoil on real constructions. And the rest lies in the training. And in the fact that the recoil won't be nearly as aggressive as in the real life. Far from that.
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Re: Simulated recoil on heavy cannons

Unread postAuthor: Ragnarok » Tue Feb 06, 2018 2:04 am

Sear wrote:- that part could be mitigated by physical restrains that protected the gunner from sticking parts of the body in the way of the recoil on real constructions. And the rest lies in the training. And in the fact that the recoil won't be nearly as aggressive as in the real life. Far from that.

I'm very much of the Murphy's Law school of thought. If it can go wrong, it will.

I've twice had valves fail in a fashion that only didn't fire a loaded launcher because I'd installed safety features that almost no-one else does. One of those failed valves was rated to fifteen times the pressure I was using it at.

You need to consider what would happen if something similar occurred while someone was loading. As it is, your current design would be perfectly capable of recoiling while the breech is open and someone's hand is in the way.

If you're expecting people to use it "in combat", the design needs to be as failureproof and foolproof as possible, because eventually something will fail or someone will work it wrong.
That's not too dangerous when it's a question of a foam slug shooting off down range, but when you've got solid metal machinery lurching around someone could be hurt.

If you are going to make it recoil, design it in a way where it cannot possibly go wrong - don't rely on safety training.
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