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Old 10-06-2014, 10:23 AM   #1
Varyon
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Default Effects of Body Mass

A new houserule I've been considering is formalizing the "special effects" of a character's body mass (weight) into actual effects, and I'm looking for a listing of relevant factors. This assumes divorcing mass and HP* - someone with higher HP than their mass indicates is someone who is particularly resilient, for example. Here's what I have so far.

Grappling: In Technical Grappling, mass is important for determining grappling encumbrance - light foes are easy to move around, heavy are more difficult. This also applies to more traditional encumbrance when someone needs to carry a character around, haul them up using a rope, and so forth. This seems a net Advantage for being heavier, although this is lessened if using the "base weight = 8xBL" alternate.

Knockback: Currently, Knockback is based on HP. It seems more appropriate to base it on mass, and someone in heavy armor is going to be a bit harder to move back as well. Advantage for being heavier.

Collisions: As with Knockback, damage from slamming or falling is currently based on HP, but mass makes more sense. This is a close call, but it seems a net Advantage for being heavier.

Blowthrough: Someone who is thin and wiry simply isn't going to absorb as much of the energy of a bullet passing through them as some hulking brute. While this makes the latter a more effective meatshield - he can absorb more damage - the fact he takes more damage in the process is problematic. Net Advantage for being lighter.

Carrying Capacity: Technical Grappling implies that an appropriate weight for a character is right around 8xBL, with extra at the very least counting against them while using mass-based moves while grappling. It may be appropriate to have this count toward encumbrance, possibly with lighter characters effectively starting with negative encumbrance. Advantage for being lighter.

Athletics: In theory, someone who is lighter but just as strong would be able to climb, jump, and so forth more easily, and may be able to run more rapidly. Using the Carrying Capacity notes, it may be appropriate to have a character who's current total weight is markedly less than 8xBL getting a bonus to such skills. The following table might work. Note weight is the character's total weight, including any carried gear, as a multiple of BL. As usual, if between two values, go with the highest.
Code:
Weight	Mod	Move	BL 20 (example)
3	+4	x1.8	60 lb
6	+3	x1.6	120 lb
7	+2	x1.4	140 lb
8	+1	x1.2	160 lb
9	0	x1	180 lb
10	-1	x0.8	200 lb
11	-2	x0.6	220 lb
14	-3	x0.4	280 lb
18	-4	x0.2	360 lb
The bonus would apply to most of the skills that Encumbrance Modifiers impact. It probably shouldn't apply to things like Karate and the like, although letting it apply to Dodge and the Parries of those skills may be appropriate. Yes, this would give a character of appropriate weight a bonus for running around stark naked. Obviously, this is a solid Advantage for being lighter.

Armor: Pyramid #3/52 has an optional rule for scaling armor surface area (and thus weight and cost) with character mass. When using this, a character's mass shouldn't modify armor by more than would be appropriate for a change in SM - that is, an SM 0 character's armor cannot weigh less than 1/2x normal or more than 2x normal, regardless of character mass. To make things more fair - and possibly more realistic - any change in surface area also modifies the maximum thickness (MaxDR) of armor the character can wear. A 50 lb SM 0 character would get away with half the weight per DR, but would also only have half MaxDR - leather armor for such a character wouldn't be able to exceed DR 2, for example. Net Advantage for being lighter.

*Optionally, HP probably shouldn't be able to vary too much from mass. A character with mass appropriate for an HP 10 character might only be allowed to have HP between 7 and 13, for example (+30%).


Anything I'm missing?

Last edited by Varyon; 10-06-2014 at 10:32 AM.
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Old 10-06-2014, 01:10 PM   #2
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Default Re: Effects of Body Mass

You're trying to dissociate mass-based effects from HP and move them to character weight. Personally, I'd do it the other way around: force HP to match body weight with only a very small margin of choice. You can play a person who's 5 feet tall and weighs 90 points, or you can play a person with 15 ST and 18 HP, but they can't be the same person; it's just not how people are put together.

I don't know exactly how to determine weight for a human based on HP, but I think I'd use Skinny and Fat as disads that characters are forced to take if their HP is too low or high for their ST, instead of the +/-30% rule.

This doesn't help you at all... so, trying to help, I think the best thing to do might be to invent "negative encumbrance" as an advantage representing the fact that your ST is much higher than your mass suggests, have that as a separate advantage that super-light things can buy (I'm thinking about ultra-tech superlight robots as much as skinny people), and let the rest of the effects equal out to net 0.
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Old 10-06-2014, 01:32 PM   #3
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Default Re: Effects of Body Mass

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Originally Posted by McAllister View Post
I don't know exactly how to determine weight for a human based on HP, but I think I'd use Skinny and Fat as disads that characters are forced to take if their HP is too low or high for their ST, instead of the +/-30% rule.
GURPS currently seems to assume an average ST/HP 10 human is right around 150 lb. This implies you can get HP for a human by taking the cube root of weight and multiplying by around 1.88. However, I think Douglas Cole got a better value by multiplying BL by 8, so I'd be more inclined to go with that. "Appropriate weight for a 12 HP character" would thus be 230 or so pounds.

Quote:
Originally Posted by McAllister View Post
I think the best thing to do might be to invent "negative encumbrance" as an advantage representing the fact that your ST is much higher than your mass suggests, have that as a separate advantage that super-light things can buy (I'm thinking about ultra-tech superlight robots as much as skinny people), and let the rest of the effects equal out to net 0.
I'm intending to try to work out estimates for what each aspect is worth, but the first step to doing that is determining what all those aspects are. As for negative encumbrance, that's a modified version of Payload (you can't store stuff inside of you, so call the Limitation "External" or something at somewhere around -20-50%), with boosted Basic Move and something like a Talent for the various affected skills. Set the Payload as an Alternate Ability to those traits, and give the traits a Limitation like "Cannot Carry Objects" and you've got it. Some weird "Already Encumbered" Disadvantage (for heavy characters) would be more difficult to work out, although simply inverting the point cost of "Negative Encumbrance" might work out.

Last edited by Varyon; 10-06-2014 at 01:35 PM.
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Old 10-06-2014, 01:58 PM   #4
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Default Re: Effects of Body Mass

Quote:
Originally Posted by Varyon View Post
GURPS currently seems to assume an average ST/HP 10 human is right around 150 lb. This implies you can get HP for a human by taking the cube root of weight and multiplying by around 1.88. However, I think Douglas Cole got a better value by multiplying BL by 8, so I'd be more inclined to go with that. "Appropriate weight for a 12 HP character" would thus be 230 or so pounds.
Multiplying BL by 8 is really clean and I like it, but the problem is that it's based on ST, and if I were designing the system, I would base mass on HP. So, build a character, divide the HP by 2, cube that, and you've got the low estimate of your character's mass: you can increase that by up to 20% of that to determine your character's mass. If you want a weight outside that range, buy a different HP. I might even have Skinny and Fat exist as leveled traits, and you must buy 1 level of Skinny/Fat for each 10% beyond the first that your HP varies from your ST.
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Old 10-06-2014, 02:20 PM   #5
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Default Re: Effects of Body Mass

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Originally Posted by McAllister View Post
Multiplying BL by 8 is really clean and I like it, but the problem is that it's based on ST, and if I were designing the system, I would base mass on HP.
If you like the 8*BL system, then simply use HP instead of ST in the equation - so weight is equal to (8/5)*(HP^2).

Skinny and Fat certainly should still get some mention, although I'd be more inclined to just do those as things like Distinctive Feature (easier to pick out in a crowd) and possibly situational skill bonuses (like being Fat making you more buoyant). I'd go with your suggestion - HP being too much lower than it should be means the character becomes Fat (to some degree), too much higher means the character becomes Skinny (to some degree). I'll have to decide on actual breakpoints, although +20% then every 10% isn't bad.
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Old 10-06-2014, 02:25 PM   #6
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Default Re: Effects of Body Mass

In my games you can just purchase HP with the massless +0% modifier. Only your regular HP counts towards calculating mass-based effects which is a hindrance about as often as it is a help. Think I stole that from Bruno.
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Old 10-06-2014, 02:36 PM   #7
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Default Re: Effects of Body Mass

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Originally Posted by Crakkerjakk View Post
In my games you can just purchase HP with the massless +0% modifier. Only your regular HP counts towards calculating mass-based effects which is a hindrance about as often as it is a help. Think I stole that from Bruno.
Can you purchase HP-less mass? HP with a special -100% modifier that only counts towards calculating mass-based effects?
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Old 10-06-2014, 03:08 PM   #8
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Default Re: Effects of Body Mass

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Originally Posted by Crakkerjakk View Post
In my games you can just purchase HP with the massless +0% modifier. Only your regular HP counts towards calculating mass-based effects which is a hindrance about as often as it is a help. Think I stole that from Bruno.
Fairly certain I originally saw that in a Krommpost, and it's part of what inspired this thread. I'm essentially intending to allow a Massless modifier for HP (as well as allowing for mass without HP), but I need to figure out what all mass should affect to determine if having different mass than your HP indicates is an Advantage, Disadvantage, or Feature. Right now, it's looking like being light is a net Advantage, being heavy a net Disadvantage, so I've made this thread primarily to see if I've missed any factors, and secondarily to start working out a fair price.

As it stands, being heavier than your HP indicate makes you a bit better at mass-based grappling maneuvers, makes you harder to shove around, allows you to cause more damage when you slam into foes (or are slammed into by them), makes you more effective cover from explosions and bullets, and allows you to wear thicker armor. Unfortunately, it also means you take more damage when you fall, take more damage when shot at by weapons capable of overpenetrating lesser men, can't carry as much around without getting slowed down, and have to wear heavier armor to get the same DR as lesser men. On the flip side, being lighter makes you not as good in a grapple, easier to toss around, etc, but effectively gives you IT:DR against high-damage bullets, get a bonus to certain tasks when completely unencumbered (and can carry more around when at least partially encumbered), and while you can't wear as thick of armor, your armor is far lighter. Egads!
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Old 10-06-2014, 05:40 PM   #9
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Default Re: Effects of Body Mass

Quote:
Originally Posted by McAllister View Post
Can you purchase HP-less mass? HP with a special -100% modifier that only counts towards calculating mass-based effects?
I don't see why not. Or you could buy negative HP with Massless?
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Old 10-06-2014, 08:08 PM   #10
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Default Re: Effects of Body Mass

Quote:
Originally Posted by Varyon View Post
GURPS currently seems to assume an average ST/HP 10 human is right around 150 lb. This implies you can get HP for a human by taking the cube root of weight and multiplying by around 1.88. However, I think Douglas Cole got a better value by multiplying BL by 8, so I'd be more inclined to go with that. "Appropriate weight for a 12 HP character" would thus be 230 or so pounds.
I use weight = (HP/2)^3, which gives 125 lbs. for 10 HP, and 167 lbs. for 11 HP. I don't quite like having weight be a multiple of BL, because BL varies as an area (cross sectional area of limbs) but weight should vary as a volume.

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