Zero-G combat rules

[Moofaa]

I am tooling around with a sci-fi setting and decided its some to finalize how to handle gravity in combat.

I decided that all planets and spaceships with gravity generators will conveniently have earth-like gravity to avoid having to create a bunch of charts and crap for determining exact penalties. Also my players and I both have a 'rules-lite' preference for gaming so this eliminates a lot of unnecesary crunch.

However for Zero-G situations I feel that some simple rules are in order. I looked in the SWR main guide and suprisingly didnt see any existing rules so I decided to make my own.

So a -6 penalty is imposed on all melee and ranged attacks right off the top. To offset this for characters that want to have an edge in these situations I decided a Zero-G Training feat would be in order, to reduce this penalty to -4.

Since combat in my games has a tendency to involve lots of risk, funny moments, and crazy multiple 1s and 20s I decided it would be fun to add one more step to combat in Zero-g environs.

When struck with a an attack the target must make a Reflex save vs a DC to maintain their footing, otherwise they go spinning round and round and have to take a full round or maybe just a move action to regain control. I was thinking of having the DC set at the amount of damage dealt, but not sure how well that would work out.

Any suggestions on how to balance this for maximum efficiency and good times?

[Ossian]

I am tooling around with a sci-fi setting and decided its some to finalize how to handle gravity in combat.

I decided that all planets and spaceships with gravity generators will conveniently have earth-like gravity to avoid having to create a bunch of charts and crap for determining exact penalties. Also my players and I both have a 'rules-lite' preference for gaming so this eliminates a lot of unnecesary crunch.

However for Zero-G situations I feel that some simple rules are in order. I looked in the SWR main guide and suprisingly didnt see any existing rules so I decided to make my own.

So a -6 penalty is imposed on all melee and ranged attacks right off the top. To offset this for characters that want to have an edge in these situations I decided a Zero-G Training feat would be in order, to reduce this penalty to -4.

Since combat in my games has a tendency to involve lots of risk, funny moments, and crazy multiple 1s and 20s I decided it would be fun to add one more step to combat in Zero-g environs.

When struck with a an attack the target must make a Reflex save vs a DC to maintain their footing, otherwise they go spinning round and round and have to take a full round or maybe just a move action to regain control. I was thinking of having the DC set at the amount of damage dealt, but not sure how well that would work out.

Any suggestions on how to balance this for maximum efficiency and good times?


Rules-lite are full of win. However, DC = damage seems a bit low.If you are going for HP = actual damage, I would double the DC. You get a stab (4 hp) at 0-g, you want the DC to be at least 8. If you get clubbed at full force (say a crit, x2, 12 damage) I think it´s kosher to give it a 24 DC. Higher damages should just send you spinning and agonizing in the corner of a room :)

However, if you go by HP of the target = vitality or ability to turn it into a grazing blow, I would stick to the "size" of the weapon. which penalizes firearms a bit (they are small to medium, usually) but it makes sense if you consider that keeping your balance in a zer-g melee seems way more difficult than trying to avoid being in the line of fire of a weapon (notice that I did not say "dodge the bullets". No one dodges a bullet. There are only misses and target well placed in terms of angle or cover).

Say a base DC of 10 per size category (so to keep your balance if a weapon is simply swinged at you is 10 for a dagger or a pistol shot, 20 for a sword or a rifle shot, 30 for a large weapon or a cannon ball). Perhaps you can add an extra DC if you are actually hit by the weapon, but then again, as I said you can see the HP as vitality, hence even a 6d8 e-web blaster shot is a "near miss" until it actually hits you, and the blast turns your body into something about the consistency of charred toothpaste...

[Moofaa]

Rules-lite are full of win. However, DC = damage seems a bit low.If you are going for HP = actual damage, I would double the DC. You get a stab (4 hp) at 0-g, you want the DC to be at least 8. If you get clubbed at full force (say a crit, x2, 12 damage) I think it´s kosher to give it a 24 DC. Higher damages should just send you spinning and agonizing in the corner of a room :)

However, if you go by HP of the target = vitality or ability to turn it into a grazing blow, I would stick to the "size" of the weapon. which penalizes firearms a bit (they are small to medium, usually) but it makes sense if you consider that keeping your balance in a zer-g melee seems way more difficult than trying to avoid being in the line of fire of a weapon (notice that I did not say "dodge the bullets". No one dodges a bullet. There are only misses and target well placed in terms of angle or cover).

Say a base DC of 10 per size category (so to keep your balance if a weapon is simply swinged at you is 10 for a dagger or a pistol shot, 20 for a sword or a rifle shot, 30 for a large weapon or a cannon ball). Perhaps you can add an extra DC if you are actually hit by the weapon, but then again, as I said you can see the HP as vitality, hence even a 6d8 e-web blaster shot is a "near miss" until it actually hits you, and the blast turns your body into something about the consistency of charred toothpaste...

Those are some sweet ideas, I hadn't considered using weapon size as a factor. I do use a vitality/wound system.

I am thinking of putting in one last rule, if your in the vacuum of space engaged in combat (like crawling around on the outside of a large ship) and take wound damage that might risk puncturing your suit.

[Kuma Kode]

d20 Future had some simple enough rules that covered all the different kinds of gravity in wide brush strokes. You can check it out on the d20 Resources site here (http://www.d20resources.com/future.d20.srd/environments/gravity.php). The Zero-G Training feat negates the penalties for low and zero gravity.

This may not be helpful if you're not running a d20 game...

I also house-ruled that any damage dealt that was not bludgeoning, cold, or sonic/concussive pierced the suit, which immediately began to depressurize it. There were then much more expensive suits that were offered that had a self-healing skin which would seal any holes immediately, thereby preventing the depressurization.

[Zexion]

I've noticed another problem. If you fire an arrow on Earth, it can go up to 250 meters per second. If you fire an arrow in zero gravity, you will go one way, and the arrow will go the other, at near-equal speeds. So, I would suggest having the damage of all ranged weapons halved, the DCs to avoid them halved, and have to succeed on a Reflex save equal to 3x the maximum damage of the weapon or be helpless and moving backwards at 5 ft./max damage dealt by the weapon, before the halving.So, for a throwing axe, the axe would do 1d3 damage plus half your Strength modifier, and you would have to make a DC 18 Ref save or be thrown backwards, helpless, at 30 ft./round. Does this make sense?

[Kuma Kode]

If you're a kobold.

A human's inertia is significantly higher than that of a bullet or arrow. The same amount of force that can send an arrow speeding through the air cannot send a human being the same speed. The force required to propel an arrow at 250 m/s is enough to push me back at the rate of 0.1875 m/s. So while a person firing a ranged weapon will experience a kick-back, as will anyone attacking or manipulating objects, it's small enough that a mere penalty to the relevant skill or attack roll will suffice.

[Ashtagon]

I've noticed another problem. If you fire an arrow on Earth, it can go up to 250 meters per second. If you fire an arrow in zero gravity, you will go one way, and the arrow will go the other, at near-equal speeds. So, I would suggest having the damage of all ranged weapons halved, the DCs to avoid them halved, and have to succeed on a Reflex save equal to 3x the maximum damage of the weapon or be helpless and moving backwards at 5 ft./max damage dealt by the weapon, before the halving.So, for a throwing axe, the axe would do 1d3 damage plus half your Strength modifier, and you would have to make a DC 18 Ref save or be thrown backwards, helpless, at 30 ft./round. Does this make sense?

Let's talk physics (hey, you started it).

First, an arrow typically has a velocity of 150-350 feet per second, not metres per second. Let's pick the midway point and convert it to metres, rounded off. That's 75 m/s, quite a bit lower than your 250.

An average human weighs 75 kg, and an average arrow weighs 50 grams (0.05 kg). Thanks to Newton, we know the basic backward-force on the user is an equal and opposite reaction.

force = 0.05 x 75 = 3.75

3.75 / 75 kg = 0.05 m/s (slightly under one foot per round).

The human will be pushed back at 0.05 m/s. This could be troublesome if you are floating in space. Assuming you are in a space station or otherwise have any kind of traction at all, this is basically not significant in game terms.

[Zexion]

If you're a kobold.

A human's inertia is significantly higher than that of a bullet or arrow. The same amount of force that can send an arrow speeding through the air cannot send a human being the same speed. The force required to propel an arrow at 250 m/s is enough to push me back at the rate of 0.1875 m/s. So while a person firing a ranged weapon will experience a kick-back, as will anyone attacking or manipulating objects, it's small enough that a mere penalty to the relevant skill or attack roll will suffice.
Fair enough. Oops.

[EccentricOwl]

It doesn't seem like you'd need a whole chapter, though no doubt F.A.T.A.L. in space would requier more than that.

-6 seems legitimate, but only a -4 with a feat? Imagine spending months or weeks rigorously training, only to find yourself with a circumstance bonus you could get by good roleplaying? =P

What about reducing it to a -2 or less? Hell, make it negate the penalty. It'll make the feat seem much more desirable.

-As for the reflex roll, you mentioned you were rules-lite from time to time- or at least, I inferred it.

Why not 'eyeball' it? Have the players make a save if the damage came from a source that you would normally consider to have a knockback - like being punched or shot with a projectile weapon as opposed to a burst of light from a laser.

[Mando Knight]

Let's talk physics (hey, you started it).

First, an arrow typically has a velocity of 150-350 feet per second, not metres per second. Let's pick the midway point and convert it to metres, rounded off. That's 75 m/s, quite a bit lower than your 250.

An average human weighs 75 kg, and an average arrow weighs 50 grams (0.05 kg). Thanks to Newton, we know the basic backward-force on the user is an equal and opposite reaction.

force = 0.05 x 75 = 3.75

3.75 / 75 kg = 0.05 m/s (slightly under one foot per round).

The human will be pushed back at 0.05 m/s. This could be troublesome if you are floating in space. Assuming you are in a space station or otherwise have any kind of traction at all, this is basically not significant in game terms.

1.) That's momentum, not force. Related, but not quite the same. (Newton's law states that the time derivative of the momentum of an object is equal to the sum of the forces applied on the object)
2.) No gravity, no traction unless you've got something else supplying a force normal to your contact surface.

[Milskidasith]

1.) That's momentum, not force. Related, but not quite the same. (Newton's law states that the time derivative of the momentum of an object is equal to the sum of the forces applied on the object)
2.) No gravity, no traction unless you've got something else supplying a force normal to your contact surface.

Just because there isn't gravity doesn't mean there isn't traction (I.E. friction). All you'd have to do is touch a surface and you'd slow down (slowly, if it's a very slick surface). On a space ship, you could easily stop yourself by digging your feet into the floor.

[Mando Knight]

Just because there isn't gravity doesn't mean there isn't traction (I.E. friction). All you'd have to do is touch a surface and you'd slow down (slowly, if it's a very slick surface). On a space ship, you could easily stop yourself by digging your feet into the floor.

...And you're digging your feet into the floor how? Pushing on the surface means that you push yourself away from the surface, and that won't provide any traction.

You need a normal force in order for friction to do anything. Gravity is the reason friction works here on Earth, but without some kind of bracing (hand holds, magnetics, something) to provide a continual pull towards the surface, you'll get no friction.

[Kuma Kode]

I think we've veered off unnecessarily. While your own attacks will technically push you around, the effect is too small to be worth modeling in nearly any system, particularly one in which the original poster said he/she prefers rules-lite. I think a general penalty of -6 or -4 to attack rolls and skill checks that involve movement is enough to model the awkward floatyness of zero-g, which can be negated by the Zero-G Training feat. There's no need to bring coefficients of friction and 0.8 ft./round movement into play.

[Jack of Spades]

You need a normal force in order for friction to do anything. Gravity is the reason friction works here on Earth, but without some kind of bracing (hand holds, magnetics, something) to provide a continual pull towards the surface, you'll get no friction.

While this is true, it should be noted that any place where zero-g will occur is generally made in such a way that traction with walls/ground is artificially increased (exempli gratia, the oodles of velcro on everything in a modern spacecraft, random handholds at convenient intervals, et cetera).
Go team engineers.

[Milskidasith]

While this is true, it should be noted that any place where zero-g will occur is generally made in such a way that traction with walls/ground is artificially increased (exempli gratia, the oodles of velcro on everything in a modern spacecraft, random handholds at convenient intervals, et cetera).
Go team engineers.

As with the example of velcro... even smooth objects have some "clings" to them, so you'd get friction just by touching them, albeit on a much smaller scale. Gravity wouldn't be pushing the two objects together, sure, but if you were flying in zero G and put your hand (just your hand) on an infinite wall of spaceship material, without pushing away, eventually you would stop.