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Old 11-01-2017, 06:12 PM   #1
Kopheay
 
Join Date: Jul 2017
Default Knockback and Realism

I was thinking about some ultratech options, and realized a payload rifle with memory batons effectively deals 20d crushing for knockback. Thats an average 70 damage, vs an average 8 strength, which means 8 yards knockback.

Now I know the 35 crushing damage should kill almost anyone to begin with, but the payload rifle isnt a gyroc weapon. Surely all the force that your target experiences should be equally applied to you in the form of kickback.

Normally gun knockback isnt a problem because piercing damage does 0 knockback, but in cinematic settings they tend to anyway, which we know is just for entertainment. The closest thing to knockback a gunshot could really cause is stumbling and falling from the sudden shift in balance, and admittedly painful force (like wearing an armor plate makes it feel like a really hard punch/kick).

So I'm thinking 1 yard knockback from impact and stumbling, 1 more from tripping or falling backward in shock seems reasonable. Should firearm knockback be capped at 2 yards?

In fact, for similar newtonian reasons, should all knockback be limited?

I propose an equation of (your SM) - (target SM) + 2 = hardcap on yards of knockback. Thoughts?
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Old 11-01-2017, 08:00 PM   #2
lwcamp
 
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Default Re: Knockback and Realism

You could just set the maximum knockback equal to the step of the thing that was hit. This represents it stumbling back from the shock of the impact rather than from momentum transfer.

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Old 11-01-2017, 08:25 PM   #3
AlexanderHowl
 
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Default Re: Knockback and Realism

Knockback is realistic, and I really do not think that 8 yards of knockback is that much trouble.
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Old 11-01-2017, 08:54 PM   #4
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Default Re: Knockback and Realism

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Originally Posted by AlexanderHowl View Post
Knockback is realistic, and I really do not think that 8 yards of knockback is that much trouble.
It really isn't. There's conservation of linear momentum to deal with. If a bullet, colliding inelastically with a foe, transfers enough momentum to them for them to fly back, say, two yards, then the bullet itself must have had that much momentum. But it started out unmoving in the gun barrel. When it acquired the forward momentum, the gun must have acquired an equal backward momentum; so either it would have flown out of the shooter's grip, or it would have hurled the shooter back a comparable distance. And that doesn't happen, and would be a very bad design for a ranged weapon.
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Old 11-01-2017, 09:00 PM   #5
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Default Re: Knockback and Realism

A solution I had been considering is to keep the DX check to stay standing, and the penalty based on the number of yards, but reduce the actual yards traveled to zero or one, depending on the circumstances
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Old 11-01-2017, 09:14 PM   #6
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Default Re: Knockback and Realism

Note that in High-Tech Baton and Beanbag rounds divide damage by five, turn it into crushing, and give double-knockback in the larger calibres (they also reduce penetration, range, and accuracy, but these don't matter for this discussion). While it's reasonable to assume better performance from a UT round, full damage is probably a bit much. I'd look at dividing damage by four, which in this case would give 2d+2(0.25) cr dkb. That's still about 18 points of knockback (technically in Basic it's 9-points, with distance doubled, but I just double the damage as Martial Arts does), enough to knock the average person back 2 yards and force a knockdown check at -1. It's high enough to be useful, but low enough that I could believe the firer doesn't suffer an equal effect because of bracing, weapon design, etc.
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Old 11-01-2017, 09:32 PM   #7
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Default Re: Knockback and Realism

I do think that being braced to deliver an attack vs. being in the midst of combat and suddenly shoved from an unpredictable direction ought to make a difference. I agree completely that Newton has something to say about the "shov-ee" vs. the "shov-er," but "the shooter will be knocked back as much as the target" assumes both are like dry-ice pucks. If one is effectively dug in with cleats for the instant it takes to fire the shot and the other is basically a dry-ice puck, zipping around unbraced, then you won't see this symmetry. That's why, for instance, a push kick can shove the victim several metres away without the aggressor moving.
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Old 11-01-2017, 09:56 PM   #8
Anthony
 
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Default Re: Knockback and Realism

The big issue with knockback is that in GURPS it's linked to damage, which doesn't actually have much to do with momentum. A 12 gauge shotgun slug might be 1 ounce at 1800 fps, equivalent to 1 lb at 112 fps, or 0.75 fps on a 150 lb human, or 3.5 lbf * seconds. By comparison, a walking speed (3 mph, or move 1.5) collision is 6x as much momentum.
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Old 11-02-2017, 03:07 PM   #9
Kopheay
 
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Default Re: Knockback and Realism

Quote:
Originally Posted by Kromm View Post
I do think that being braced to deliver an attack vs. being in the midst of combat and suddenly shoved from an unpredictable direction ought to make a difference. I agree completely that Newton has something to say about the "shov-ee" vs. the "shov-er," but "the shooter will be knocked back as much as the target" assumes both are like dry-ice pucks. If one is effectively dug in with cleats for the instant it takes to fire the shot and the other is basically a dry-ice puck, zipping around unbraced, then you won't see this symmetry. That's why, for instance, a push kick can shove the victim several metres away without the aggressor moving.
True, but in this extreme scenario it is imparting roughly 9 m/s onto a roughly 80kg target. That sort of shove just seems too momentous to completely shrug off by having good poise.


Quote:
Originally Posted by Rupert View Post
full damage is probably a bit much. I'd look at dividing damage by four, which in this case would give 2d+2(0.25) cr dkb. That's still about 18 points of knockback (technically in Basic it's 9-points, with distance doubled, but I just double the damage as Martial Arts does), enough to knock the average person back 2 yards and force a knockdown check at -1.
I like the result, but dislike the method of getting there. The way I see it, ordinary knockback rules worked great, until you scaled up to the immense weapons of speculative fiction. This solution solves the problem at hand, but still is vulnerable to superscaling. Not to mention it would make memory batons underwhelming in smaller guns.
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Old 11-02-2017, 04:36 PM   #10
Anthony
 
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Default Re: Knockback and Realism

The easy solution is: 'only slams do knockback'. It's not totally true, but the exceptions tend to be powerful enough that knockback is the least of your problems (for example, the tank cannon in UT would cause knockback to a human; the fragments of the corpse would probably be spread as much as twenty yards away from the point of impact).
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