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Railguns and other tech, appropriate skill type
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vanir
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PostPosted: Tue Apr 03, 2012 8:00 pm    Post subject: Railguns and other tech, appropriate skill type Reply with quote

In some supplements railguns are expressed as a firearms specialisation, others a separate skill, concussion weapons and pulsewave weapons are often expressed as a separate skill, I wanted to open discussion about this.

Railguns firstly don't recoil, well they do but it's out of all proportion the the force of the projectile, more like a baby tap with a howitzer on the action side.
This is because the reaction if you will, to the force driving the projectile is expressed laterally, between the rails which have a slight problem not being forced apart in real world versions, and wearing very quickly when they aren't.

In this sense they act just like a recoilless rifle for the firer, given this is a fictional star wars handheld weapon, still the closest analogue I've got.
So I say it's a missile weapons specialisation, like a bazooka or any other recoilless rifle is a missile weapon. Same skill, projectiles are just ultra-high velocity instead of powered but still usually fin stabilised, explosive, etc.

Should rule a +1D damage versus hard armour natural AP quality however, simply due to projectile velocity in the moonlaunch category.


Pulsewave weapons too, I like using the Archaic Weapons skill for this, since I reckon a black powder firearm is just a specialisation of firearms, there's no significant change from a colt navy to a colt peacemaker except the noise, smoke, noise and noise and a slight delay for s*** powder. Even rifled versus non rifled really just varies hit probability, it's the same "lobbing" skill to at least try to put a projectile onto a target.

So I use Archaic Weapons for certain alien or archaic blaster technologies, but very generalised, like Beam Weapons (the traditional sci-fi laser gun, no gases), and Pulse Wave Blasters (older blaster weapons for Old Republic campaigning, just half range, half ammo blasters of "a non-descript older tech")


Curious about concussion rifles though. I take it these are like man portable artillery to a degree, fires a concussive projectile which deals concussion damage in a small radius, but also acts as a direct fire weapon.

Aren't these somewhere between firearms and missile weapons?



I mean I really don't like the idea of having a full skill for every type of weapon using a similar method of placing rounds on a target, because that's what specialisations are supposed to be for and my characters need mechanical and perception and technical skills to survive a combat zone, we don't just do hack and slash in our games.


So where have a lot of you guys come down on some of these interesting and useful, unusual weapons in terms of appropriate skill use and gameplay?
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Downstrike
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PostPosted: Tue Apr 03, 2012 9:51 pm    Post subject: Reply with quote

On the concussion...
A flash bang grenade just uses the blast overpressure effect of most high explosives while not producing the frag effect [though secondard frag from say gravel is still possible] with the heavy body for the explosive charge. They work great in enclosed areas but do cause physical damage like popping ear drums and the like. In open areas, like riots, they are very cool firecrackers. As with any explosive, standoff is you friend. Being right on top of it in the open can be worse than being across an enclosed room with one going off. That being said, I don't know of a 40mm version...thats when you get into CS gas....but that doesn't mean its not out there.

So I'm not sure if that helps but if you want to PM me on grusome details, you know where I'm at.

Cheers
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vanir
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PostPosted: Tue Apr 03, 2012 10:40 pm    Post subject: Reply with quote

Interesting about concussion damage. Have wondered about that for concussion grenades.

At first I used them as analoguous to frag grenades except instead of working against armour physical damage, they worked against the energy damage rating.

That was mostly just to throw it around a bit and make them different to frag grenades in gaming terms.

I guess the correct way to handle them, is physical damage vs armour only if the wearer is in a fully suit with an enclosed helmet or specified concussion protection.

Otherwise, say with a blast vest alone, or say you're wearing scout armour but no helmet, well you wouldn't get any armour protection from a concussive blast really would you? I mean it's still going to mush your brains inside the skull a bit either way to do its lethal damage if it's a lethal rating.
?
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Fallon Kell
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PostPosted: Tue Apr 03, 2012 11:05 pm    Post subject: Reply with quote

First of all, railguns do have recoil proportional to the damage on target, just like firearms. If you have 5,000 foot-pounds of muzzle energy, you're gonna have about twice the recoil of a .30-30. If you have 5,000,000 foot-pounds of muzzle energy, your recoil will be more in line with that of a tank cannon.

I house rule the division of marksmanship skills into handguns and long guns, rather than blasters and firearms, but before I did that, I always treated railguns as a specialization of firearms, since they work so similarly to the user.

Concussion weapons as you described would be missile weapons, I think, but I've always thought they were supposed to be more along the lines of what we see the Geonosians using in Episode II–collimated shock wave cannons.

Finally, I just wanted to clarify: flashbangs don't use high explosives, which detonate at supersonic speeds (the supersonic shockwave sets off adjacent molecules of explosives). They use low explosives which deflagrate at subsonic speeds (the heat of the reaction sets off adjacent molecules of explosives). Flashbangs and the police who use them have gotten a bad name lately amongst OWS types, and I don't like to reinforce the image that they've tried to paint of riot police throwing high explosives at peaceful demonstrators. Just a simple brick of high explosives without any shrapnel would still dismember any protestor standing within several feet. Very different from a flashbang, which is much closer to a loud firecracker in composition and application, than to a bomb.
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vanir
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PostPosted: Tue Apr 03, 2012 11:24 pm    Post subject: Reply with quote

Railguns don't have that kind of recoil. they don't vomit, they squeeze.

I mean they don't fire a projectile, they don't express a rearward force to make something go forwards.

They squeeze like squeezing soap in your hand, and it pops out. They do it like that. Hence the problem with wear on the rails and framework to keep them from shoving each other apart.

Get a sausage balloon and squeeze one end, slowly walk the squeezing hands to force the air, or the bulk of it, ahead of your lateral motion. They work like that.

There is some recoil, but it is well out of proportion to the force of the projectile.
Most modern, actual railguns however combine firearms and railgun technology, a low powered shell is fired down the rails and then accelerated, these naturally have quite a bit more recoil.

On a purist railgun, the reason they were a popular idea for the 70s-80s strategic space defence network proposals, is because they won't unduly mess up the orbit of a satellite firing one. Nothing that can't be corrected by some tiny oxy thrusters.
The vast bulk of the force is expressed between the rails. One field and another field pressing against each other, timed coils, easy. In fact with a fin stabilised projectile there's no reason it can't be suspended within the field as soon as it enters it. Most everything to do with recoil is dependent on the action anyway, not the muzzle velocity.
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thedemonapostle
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PostPosted: Tue Apr 03, 2012 11:40 pm    Post subject: Reply with quote

heres a good video of a real world railgun shooting a 40lb non-aerodynamic projectile at 4,500-5,000 miles per hour. video clearly shows recoil, but it does fire a 40lb projectile

http://www.foxnews.com/scitech/2012/02/28/its-real-navy-test-fires-first-working-prototype-railgun/
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Fallon Kell
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PostPosted: Tue Apr 03, 2012 11:51 pm    Post subject: Reply with quote

vanir wrote:
Railguns don't have that kind of recoil. they don't vomit, they squeeze.

I mean they don't fire a projectile, they don't express a rearward force to make something go forwards.

They squeeze like squeezing soap in your hand, and it pops out. They do it like that. Hence the problem with wear on the rails and framework to keep them from shoving each other apart.

Get a sausage balloon and squeeze one end, slowly walk the squeezing hands to force the air, or the bulk of it, ahead of your lateral motion. They work like that.

There is some recoil, but it is well out of proportion to the force of the projectile.
Most modern, actual railguns however combine firearms and railgun technology, a low powered shell is fired down the rails and then accelerated, these naturally have quite a bit more recoil.

On a purist railgun, the reason they were a popular idea for the 70s-80s strategic space defence network proposals, is because they won't unduly mess up the orbit of a satellite firing one. Nothing that can't be corrected by some tiny oxy thrusters.
The vast bulk of the force is expressed between the rails. One field and another field pressing against each other, timed coils, easy. In fact with a fin stabilised projectile there's no reason it can't be suspended within the field as soon as it enters it. Most everything to do with recoil is dependent on the action anyway, not the muzzle velocity.
Every action has an opposite and equal reaction. That slug going forward out of a railgun barrel is an action. The railgun must then also go back into your shoulder with force proportional to the slug fired. The soap you squeeze from your hand also recoils against your hand, opposite to the direction of motion. If that soap shot forward with about 2,800 foot pounds of energy, your hand would suffer the same recoil as my shoulder when I fire my .30-06. More importantly, if I were to fire a 180 grain projectile from an 8lb railgun at 2700 feet per second, it would feel exactly the same as firing my rifle.

It doesn't matter if that projectile's motion comes from an explosion or a squeeze; it comes from the gun pushing on it... and the slug pushes back.

Wikipedia wrote:
Materials used
The rails and projectiles must be built from strong conductive materials; the rails need to survive the violence of an accelerating projectile, and heating due to the large currents and friction involved. The recoil force exerted on the rails is equal and opposite to the force propelling the projectile. The seat of the recoil force is still debated. The traditional equations predict that the recoil force acts on the breech of the railgun. Another school of thought invokes Ampère's force law and asserts that it acts along the length of the rails (which is their strongest axis).[7] The rails also repel themselves via a sideways force caused by the rails being pushed by the magnetic field, just as the projectile is. The rails need to survive this without bending, and must be very securely mounted.
(Italics and bolding mine)
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vanir
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PostPosted: Wed Apr 04, 2012 3:46 am    Post subject: Reply with quote

Well clearly I've managed to confuse myself severely.

Yet when I stand upon a sheet of ice in slippery shoes,
and I throw a basketball away from me, it seems to me I should move backwards more, than if I squeezed the basketball between my hands and it popped forwards from me at the same velocity. I mean I'm talking about Lorentz Force, as opposed to linear Force. Part of the body of Force is in a triangular shape and not a straight line.
edit. I got it now, it means I need much more Force pressing together to get the same velocity on the basketball.

Consider the explosive/gaseous drive of a firearm exerts at the rearmost of the projectile and recoils against the breech

Consider that Lorentz Force is used between a negative and positive rail, the armature-railcar doesn't need to be a physical sabot but maybe a plasma (allowing a gaussian style suspension of the projectile in space, removing friction)

But you're right, I've confused myself, the source of propulsion is along the rails, so there would be recoil for the momentum of the projectile along the rails, however not directly against a breech block because of Lorentz Force (perpendicular recoil to Force presented, that's the rule, but the housing...okay I see this).

There would be much more recoil with a solid armature-railcar however, a sabot like our real world tech uses. There'd be noticeably less with a plasma like SW tech would use.
And the Lorentz Force is still spreading some of the recoil laterally, not quite every bit of it will go lengthways along the rails, unless you've got a great big heavy sabot-armature or a huge projectile.

You can use very small projectiles at supervelocity with low recoil for tremendous kinetic energy. In man portable Star Wars form it should still be a low recoil weapon.

But not recoilless as I asserted.
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Bren
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PostPosted: Wed Apr 04, 2012 5:37 am    Post subject: Reply with quote

]A railgun is not a firearm as it does not use a chemical propellant. It is electrically powered and accelerates a conductive projectile along electromagnetic rails.

Newton's Third Law tells me the a railgun is no more recoiless than any other projectile weapon though whether the recoil is predominantly directed along the breech or the rails seems undetermined. From Wiki:
Quote:
Materials used

The rails and projectiles must be built from strong conductive materials; the rails need to survive the violence of an accelerating projectile, and heating due to the large currents and friction involved. The recoil force exerted on the rails is equal and opposite to the force propelling the projectile. The seat of the recoil force is still debated. The traditional equations predict that the recoil force acts on the breech of the railgun. Another school of thought invokes Ampère's force law and asserts that it acts along the length of the rails (which is their strongest axis). The rails also repel themselves via a sideways force caused by the rails being pushed by the magnetic field, just as the projectile is. The rails need to survive this without bending, and must be very securely mounted.

Heat dissipation

Massive amounts of heat are created by the electricity flowing through the rails, as well as by the friction of the projectile leaving the device. The heat created by this friction itself can cause thermal expansion of the rails and projectile, further increasing the frictional heat. This causes three main problems: melting of equipment, decreased safety of personnel, and detection by enemy forces. As briefly discussed above, the stresses involved in firing this sort of device require an extremely heat-resistant material. Otherwise the rails, barrel, and all equipment attached would melt or be irreparably damaged.

In practice the rails are, with most designs of railgun, subject to erosion due to each launch; and projectiles can be subject to some degree of ablation also, and this can limit railgun life, in some cases severely.


Heat may be a problem for a sniper since it may make detection via thermal imagery or alien senses quite easy.

A railgun appears as a weapon in one of the WEG scenarios and they got the recoil correct as the arachnid being that uses a railgun is quite strong.
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atgxtg
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PostPosted: Wed Apr 04, 2012 10:44 am    Post subject: Reply with quote

Uh guys,1)since the force is being applied an oppising angles, most of the recoil won't be concentrated directly to the real of the projectile. That means that a lot of the recoil force would be applied in two opposite directions and cancel out.

The firing weapon, vehicle, whatever would still need to absorb the stress of firing, but the net movement could be very low.If the rail were a spiral, then even more of the recoil could be balanced off.

But, nothing says that the railgun has to push the bullet. If you put a charge on the front ofhte railgun it could pull the bullet down the rail as well as push it from behind. The the two forces could conceivably cancel out.

And, the easy way to do it would be to have two railguns mounted back. That is what modern recoilless weapons do. Firing a heavier, slower moving mass of particles, or powered metal would do the trick. Although that wouldn't help as far as space clutter goes.



I think the major advantage of railguns isn't low recoil, but the elimination of the explosive propellants. That makes the weapons safer, makes it easier to store ammo , lets you store a lot more ammo in a given space, and gets around the velocity limitation inherent in chemical propellants.
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PostPosted: Wed Apr 04, 2012 1:52 pm    Post subject: Reply with quote

vanir wrote:
Well clearly I've managed to confuse myself severely.

Yet when I stand upon a sheet of ice in slippery shoes,
and I throw a basketball away from me, it seems to me I should move backwards more, than if I squeezed the basketball between my hands and it popped forwards from me at the same velocity. I mean I'm talking about Lorentz Force, as opposed to linear Force. Part of the body of Force is in a triangular shape and not a straight line.
edit. I got it now, it means I need much more Force pressing together to get the same velocity on the basketball.

Consider the explosive/gaseous drive of a firearm exerts at the rearmost of the projectile and recoils against the breech

Consider that Lorentz Force is used between a negative and positive rail, the armature-railcar doesn't need to be a physical sabot but maybe a plasma (allowing a gaussian style suspension of the projectile in space, removing friction)

But you're right, I've confused myself, the source of propulsion is along the rails, so there would be recoil for the momentum of the projectile along the rails, however not directly against a breech block because of Lorentz Force (perpendicular recoil to Force presented, that's the rule, but the housing...okay I see this).

There would be much more recoil with a solid armature-railcar however, a sabot like our real world tech uses. There'd be noticeably less with a plasma like SW tech would use.
And the Lorentz Force is still spreading some of the recoil laterally, not quite every bit of it will go lengthways along the rails, unless you've got a great big heavy sabot-armature or a huge projectile.

You can use very small projectiles at supervelocity with low recoil for tremendous kinetic energy. In man portable Star Wars form it should still be a low recoil weapon.

But not recoilless as I asserted.


The 'recoil' from throwing the basketball isnt from the basketball leaving your body, but from your body making the throwing movement. In effect it isnt 'recoil' but 'torque' (best I can come up with in english).

The recoil effect is the same (ie almost non existent given the mass and speed of the ball in comparison to your own mass).
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Bren
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PostPosted: Wed Apr 04, 2012 3:11 pm    Post subject: Reply with quote

atgxtg wrote:
Uh guys,1)since the force is being applied an oppising angles, most of the recoil won't be concentrated directly to the real of the projectile...
I'd like to see the vector arithmetic for that. Because that sounds wrong.
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ZzaphodD
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PostPosted: Wed Apr 04, 2012 4:11 pm    Post subject: Reply with quote

Bren wrote:
atgxtg wrote:
Uh guys,1)since the force is being applied an oppising angles, most of the recoil won't be concentrated directly to the real of the projectile...
I'd like to see the vector arithmetic for that. Because that sounds wrong.


If the force wouldnt be directed forward but instead just 'squeezed', then the projectile wouldnt leave the barrel... Laughing
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atgxtg
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PostPosted: Thu Apr 05, 2012 9:42 am    Post subject: Reply with quote

ZzaphodD wrote:
Bren wrote:
atgxtg wrote:
Uh guys,1)since the force is being applied an oppising angles, most of the recoil won't be concentrated directly to the real of the projectile...
I'd like to see the vector arithmetic for that. Because that sounds wrong.


If the force wouldnt be directed forward but instead just 'squeezed', then the projectile wouldnt leave the barrel... Laughing


True. I set that up wrong. What I emant as for the forcs to be applies at an angle other than 0 degrees or 90 degrees. But even that idea was incorrect as you'd still get recoil from the force that did move the projectile forward.

My bad.

Howoever, nothing says that the velocity needs to be applied all at once. You could greatly reduce the recoil by applying less force over a longer peroid of time. For example. lets say that you have a railgun that acclerates a 10g projectile to 300m/s., in 1/100th of a second. Doing the math:



V=at; V-300m/s, t=.01s;
a=V\t, or 30000 m/s

F=ma; m=10g, a-30000m/s; F= 300 N-m (the force, or"recoil").

Barrel Length = 1/2at^2; a-30000, t=.001; Length 1.5m


Now if we were to reduce the rate of accleration, but apply it over a longer time peroid, we could reduce the recoil force. For example, lets say we take 1/10th of a second to reach 300m/s.

a=V/t; a- 3000m/s

F=ma; F= 30N-m (that's one tenth the recoil)

Barrel length: 1/2at^2; Barrel Length: 15m



So you can recue the recoil force. You would still need to deal with it, and the total force would be the same, but it would be easier to offset a snaller force over a longer time period.
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Bren
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PostPosted: Thu Apr 05, 2012 12:29 pm    Post subject: Reply with quote

atgxtg wrote:
But even that idea was incorrect as you'd still get recoil from the force that did move the projectile forward.
Glad we cleared that up. Wink

atgxtg wrote:
Howoever, nothing says that the velocity needs to be applied all at once.
True.
Typically railguns use very high velocity projectiles. Because, as you said, one advantage of using EM instead of chemical propellants is you can deliver more force. It may not matter for your example about reducing instantaneous recoil because the projectile is being accelerated along the entire barrel length, but 300m/s seems way too slow for a 10g railgun projectile.

I don't know enough about how a firearm actually works to know whether recoil is instantaneous or whether the expanding gas is effectively applying force (and hence recoil) over a longer period of time as well. Unless the barrel of the railgun is far longer the the barrel of a blaster (or firearm) I'm wondering if, given the higher muzzle velocities attributed to railguns, the recoil effect is at all decreased for the railgun in comparison to a traditional firearm.

From a weapons design perspective, even if you could build a personal railgun with a lower recoil, why not instead build a railgun with an equivalent recoil and a higher muzzle velocity, greater pellet weight, or both?
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