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 Post subject: [HOMEBREW AD&D, D&D 3.5, d20 etc] Falling damage
PostPosted: Thu Jun 12, 2008 11:51 am 
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The "1d6 per 10 feet of falling, with a maximum of 20d6" rule is simple, but not very realistic (yes, I know, we have wizards and Jedi and stuff in these games, but a little more verisimilitude for falling would be nice).

As any physicist will tell you, your momentum is what causes the damage when you hit the ground, not the distance - and small light things have a lower maximum speed when falling than big dense things.

I propose that the number of dice of damage one takes from falling be equal to one tenth of the speed in feet per second.

  • Damage = speed / 10
Of course, in an RPG, we're more aware of the distance something will fall than we are of the speed you'll be going when you hit. So, I looked up the maths, and found that in feet per second, it's quite easy to work out:

  • Speed = square root of (Distance x 64)
Armed with the speed, we can work out how many dice we need for the damage... but momentum (which is what hurts you when it's all converted into bludgeoning damage) isn't just about your speed: your weight is important too.
From the d20 modern rules for vehicle collisions, I saw that smaller objects inflict lower damage by using a smaller die type. Simple and easy to apply. In real life, hamsters can fall almost indefinitely without sustaining any injuries because they're so light and fluffy, whereas an elephant will break limbs if it falls just a dozen feet or so.
For other rules systems where size categories aren't as clearly defined, I've given examples of things that are the sizes.
  • Fine (fly) = 1
  • Diminutive (hamster) = 1d2
  • Tiny (cat) = 1d3
  • Small (halfling) = 1d4
  • Medium (adult human) = 1d6
  • Large (horse) = 1d8
  • Huge (elephant) = 1d10
  • Gargantuan (baleen whale) = 1d12
  • Colossal (Godzilla) = 1d20
Lastly, how fast do things fall before their wind resistance matches gravity? Numbering the size categories from Fine to Colossal, I found a whole bunch of examples, and made this rule:
  • Terminal Velocity = Size category squared x 10
(This rule closely follows real life terminal velocities without needing too much maths.)
Any time the distance fallen shows that the speed is higher than this amount, change it to the terminal velocity.

Summing up:
  • Falls greater than your own height risk damage
  • Number of dice = speed / 10
  • Maximum number of dice = size category squared
  • Speed = square root of (Distance x 64)
  • Type of die = one step per size category (where 'Fine' = d1)

This still means that a tough high level character can walk away from any fall (as long as he's not gargantuan). How to fix that? I suggest that half of falling damage is applied to CON, save for half (3.5 versions of D&D would use a Fortitude save with a DC equal to the number of dice, AD&D would probably use a Petrification save).

If you've read this far, thanks! I'd like your opinion: it's a big new rule - does it all add up? Would it be easy enough to use?

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Last edited by Altair-the-Vexed on Mon Jun 30, 2008 10:11 am, edited 4 times in total.

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PostPosted: Thu Jun 12, 2008 11:57 am 
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Nice rule,

As you stated some characters could essentially fall indefinitly and "walk" away, this does happen in real life although rarely. People have survived a 20,000 parachute jump with a failed chute.

Maybe you need to factor in some broken limbs though so they cant immediatly drop 20,000 feet then spring into combat?

just an idea

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PostPosted: Thu Jun 12, 2008 12:07 pm 
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Harroguk wrote:
Nice rule,

As you stated some characters could essentially fall indefinitly and "walk" away, this does happen in real life although rarely. People have survived a 20,000 parachute jump with a failed chute.

Maybe you need to factor in some broken limbs though so they cant immediatly drop 20,000 feet then spring into combat?

just an idea


That's what the CON damage is for - humans terminal velocity by these rules is 250 f/s, or 25d6, averaging out at 87.5 hp damage. Half of that damage (43.75) is applied to your CON, killing any sensible medium sized character, unless it makes a DC25 Fort save to take 21.875 - which is still enough to kill almost anyone.
On a low roll, the survivability goes up. On a high roll, you'll need a Resurrection spell.

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PostPosted: Thu Jun 12, 2008 12:15 pm 
Motor Mouth
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Cheers for clearing that up. All seems to make perfect sense to me now :)

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PostPosted: Thu Jun 12, 2008 3:13 pm 
Motor Mouth
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Take a look at Falling Damage Spreadsheet

I think I have got all the formulas correct (Columns are hidden to make displaying it easier)

The only thing you can edit is the fall distance, everything else is calculated.

Now you can ammuse yourself with the fact that humans falling 2 feet will take between 1 and 6 damage and 2 points of CON damage on average :D

Anything over 90 feet becomes tricky to survive.

I know that some of the calculations display odd results however that is due to the way Excel handles numbers rather than my bad maths :)

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 Post subject: Aaaaaargghhhhhhhh! SPLAT!
PostPosted: Thu Jun 12, 2008 3:28 pm 
This is a great rule as it takes into account the physics of falling.

But a bit too much for my liking because if we start introducing science to the game rules (such as attempting to deal with the intricacies of electricity and its wonderful effects on metal and people in water for example) we end up with a whole load of BIG rules based on RW physics that can slow play.
However, your rules have quite a happy balance (IMO)

I do not like the core falling rules as written either. Yes people have fallen 20k feet and walked away but these instances are incredibly rare (not 1 in 20 but certainly a natural 20 on their saving throw!)

My own house rule is 1d6 per 10' fallen, but cumulative. i.e. D6 at 10' 3d6 at 20', 5d6 at 30' and so on until rolling the dice becomes just a formality at say 100'. Anyone falls that far and they should be dead.
Its basic but puts the fear back into falling.

Also, HPs are abstract in that a character with 90hp being struck by an arrow for 9, has actually likely been narrowly missed or suffered a graze. The same damage to a character with 10 HP has likely stuck them in the shoulder.
The planet never misses EVER. Its base attack is just too high. (I think it would be classed as bludgeoning damage too but DR be damned!)

Hmmm, I think I am going to work on a falling rule that actually deals a percentage of damage to a falling creature.
(I wouldnt use CON due to constructs and undead becoming immune to falling)
This way, a 100HP human fighter falling from the same cliff as a 10HP fighter have the same odds as each other of dieing/walking away.
After your very well made observations (about size and mass) maybe a bonus for lighter creatures and a penalty fo heavier...

DISCLAIMER: No hamsters or elephants were harmed during the making of this house rule.


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PostPosted: Mon Jun 30, 2008 10:08 am 
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Good points about CON regarding constructs and the like, and minimum damage - thanks! I've edited the original post to allow creatures to fall up to their own height before taking damage.

Under my rule as it stands, golems and undead will take HP damage, but are less likely to be instantly destroyed by a fall. Is that necessarily a bad thing? In literature and film, undead and robots and such like tend to be difficult to break apart.

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PostPosted: Mon Jun 30, 2008 10:24 am 
Altair-the-Vexed wrote:
In literature and film, undead and robots and such like tend to be difficult to break apart.


And serial killers.


If we're going for a movie feel, there should be a special rule regarding uber bad guys and long drops with huge spikes at the bottom... (bonus XP if you manage to skewer them) ;)


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PostPosted: Tue Jul 01, 2008 9:50 am 
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Helios wrote:
If we're going for a movie feel, there should be a special rule regarding uber bad guys and long drops with huge spikes at the bottom... (bonus XP if you manage to skewer them) ;)

Indeed - that's the only way to kill the Big Bad Evil Boss. Any other "death" only results in them returning for a lower quality sequel.

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 Post subject: Re: [HOMEBREW AD&D, D&D 3.5, d20 etc] Falling damage
PostPosted: Thu Oct 22, 2009 12:20 pm 
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Always on the look out for simpler ways of doing things (despite the complexity of some of my proposals), I've hit on this calculation:

    Falling damage = XdY
  • where X = (square root of the height) - 1 [rounding down]
  • Y = damage die determined by size category [see earlier posts]
This is a far simpler calculation, and is very close to the same results as the previous long-winded calculations.

Fine and diminutive living creatures take no damage from falling, but objects, constructs and similar inanimate things do. The GM may rule that dense, brittle creatures of diminutive size or lower can take damage.

Creatures may make a Jump or Tumble check as an immediate action to attempt to reduce falling damage by 1 die (DC 15).

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