[d20a] Falling

Ashtagon's homebrew rules set.

[d20a] Falling

Postby Ashtagon » Sun Sep 13, 2009 12:01 pm

For earlier iterations and inspiration, see here and here.

Default d20 falling rules suck hard. I won't bother explaining why, they just do. Here's my revision...

Base falling damage is 1d6 per 10 feet fallen, capped at 60d6 (usually at 600 feet fallen). For purposes of damage resistance, this is considered Bludgeoning damage.

  • If you are not flat-flat-footed when you began falling, you make make a Reflex/Jump/Tumble check (choose your best one). The DC is equal to 5 per die of base damage. Success completely negates one die of damage. If you are falling/diving into water that is not deep enough to attempt a dive (described below), you can substitute a Swim check with the DC outlined here.
  • If you are not flat-footed when you began falling, and you are falling into water, you may attempt a Swim check to dive into the water. This check is instead of the Reflex/Jump/Tumble check described above. The DC is 10 (+1 per die of base damage). Success completely negates one die of damage. Each full five points the DC number is beaten by negates an additional die of damage. The water depth must be at least equal to the distance fallen or 30 feet (whichever is lower) in order to attempt a Swim check. If the water is not deep enough to perform a dive, you can instead attempt a controlled "fall" as described in the bullet point above, and use your Swim skill.
  • Falling onto a soft surface (deep mud, deep snow, cart full of straw, etc) negates an additional die of damage. Note that water is not considered a soft surface for this purpose.
  • If you fall onto a spiked pit, this is treated as a regular fall. The spikes then perform an "attack", with 1d4 attacks, bab +10, and 1d4+4 damage per attack (these numbers are based on the Traps section of the SRD).

Each die of hit point damage that is not reduced as described above also causes 1d6-3 (minimum 0) Dexterity damage.

Roll a Fort save (DC 15 +1 per die of base damage). Failure means you are stunned for one round when you land. Each point that this save DC is beaten by reduces the Dexterity damage by one point. Making the DC number exactly means you are neither stunned nor is Dexterity damage reduced.

So How Do Folk Survive Falling from Orbit or Aircraft?

If you have any action points to spare, you can spend one to cap hit point and Dexterity damage to "all but the last point".

Special; Sci-Fi Considerations

Air Pressure: The 60d6 damage cap is not affected for air pressures lower than Earth's. For higher air pressures, multiply the damage cap by (1 / cube root of air pressure). For example, Venus (95 atmospheres) would have falling damage capped at 13d6. Of course, you'll be simultaneously crushed, suffocated, dissolved, and roasted, once you land there...

Gravity: The effective distance fallen is multiplied by local gravity; a 60-foot fall on Earth's Moon (1/6 Earth-G) would be treated the same as a 10-foot fall on Earth. This can get dangerous fast on planets with high gravity. (Note that current theories of planet formation don't allow for rocky planets with surface gravities over 3 G; such bodies tend to sweep surrounding space of light elements, and become gas giants).

Air pressure and gravity considerations can be pre-calculated when the planet is designed, and left as a single sentence summary described in the planetary environment chapter.

Examples:

Venus: 1d6 damage per 10 feet, capped at 13d6.
Earth: 1d6 damage per 10 feet, capped at 60d6.
Mars: 1d6 damage per 30 feet, capped at 60d6.
Luna: 1d6 damage per 60 feet, capped at 60d6.

Orbital Re-Entry: Thermal effects of orbital re-entry coming soon.
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Re: [d20a] Falling

Postby Big Mac » Sun Sep 13, 2009 1:59 pm

Ashtagon wrote:So How Do Folk Survive Falling from Orbit or Aircraft?

If you have any action points to spare, you can spend one to cap hit point and Dexterity damage to "all but the last point".

Special Sci-Fi Environmental Considerations:

Air Pressure: The 60d6 damage cap is not affected for air pressures lower than Earth's. For higher air pressures, multiply the damage cap by (1 / cube root of air pressure). For example, Venus (95 atmospheres) would have falling damage capped at 13d6. Of course, you'll be simultaneously crushed, suffocated, dissolved, and roasted, once you land there...

Gravity: The effective distance fallen is multiplied by local gravity; a 60-foot fall on Earth's Moon (1/6 Earth-G) would be treated the same as a 10-foot fall on Earth. This can get dangerous fast on planets with high gravity. (Note that current theories of planet formation don't allow for rocky planets with surface gravities over 3 G; such bodies tend to sweep surrounding space of light elements, and become gas giants).


Spelljammer had some rules about this somewhere, but I can't recall where at the moment. I think the basic thing was that if you fell from orbit you would start to burn up from air friction before hitting the ground with maximum damage.

We will be needing to make some sort of rule for the 3e SJCS conversion. I'd be inclined to treat air friction as being a bit like the "landing on a soft surface" rule (so that a fall onto a world with air would have no limit maximum damage). SJ pretty much makes all planets have a 1G gravity, but if you want to make sci-fi rules (rather than D&D rules) I'd say you should bump up max damage for planets with high gravity and lower it for planets with low gravity.
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Re: [d20a] Falling

Postby Ashtagon » Sun Sep 13, 2009 2:18 pm

The SF considerations are specifically written to deal with RL physics, not SJ physics ;)

If you fall from orbit, you're pretty much going to hit the maximum damage for that planet anyway. The maximum damage is a function of terminal velocity, which is a function of atmospheric resistance, rather than gravity. The actual effects of air pressure are almost irrelevant to falling damage, truth be told. You'll hit that terminal velocity sooner with a high gravity planet, but the terminal velocity will be lower with a planet that has a high density atmosphere.

Incidentally, the highest density atmosphere that is normally considered breathable in SF settings is about 1.5 atmospheres. Under the formula in my OP, that would cause damage to be capped at 52d6. It still takes less dice to roll up a new character :)

I purposely ignored the thermal effects of orbital re-entry for this rule. When written, I expect it will be on the lines of "lots" of fire damage (probably 3d6 fire damage per round for n rounds; most re-entry vehicles will have fire resistance 20). The falling damage would only then be relevant if you survive the fire damage.

For SJ...

Since gravity is always either 0G or 1G, the gravity rule is irrelevant. The air pressure rule can also be ignored (treat everything as capped at 60 dice), since SJ doesn't deal with air pressure except in a binary, vacuum/Earth-normal sense. Whether orbital re-entry has thermal effects is probably something that depends on the physics of the sphere in question.

----

The main issue I am unhappy with for now is that this system requires no less than three saving throws, plus damage rolls. It's a bit too much like a dice-rolling festival for my tastes.
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Re: [d20a] Falling

Postby Havard » Sun Sep 13, 2009 2:20 pm

Slightly OT, but I love the falling rule from 7th Sea. You take no damage at all if you fall on something soft:

* Water
* A pile of Hay
* Onto the saddle of a horse

8-)

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Re: [d20a] Falling

Postby Ashtagon » Mon Sep 21, 2009 7:37 pm

Collisions

Danger: thinking out loud and extreme maths ahead.

ref pages:
http://www.safespeed.org.uk/killspeed.html

Related to falling is the impact from a vehicle.

Your final velocity from a fall is 9.80665 m/s multiplied by the time spent falling. The actual distance fallen is your average velocity over that period (ie. half your final velocity) multiplied by the time spent falling. Suitable use of conversion factors can then produce conversions for final velocities at various speeds and various distances. In short, it should be possible to equate every possible vehicle speed to an equivalent "falling distance" for damage purposes. As raw, non-massaged figures, this yields the following figures:

* Speed 0-25 mph (0-40 kmph): no meaningful damage
* Speed 25-43 mph (40-70 kmph): 1d6 damage
* Speed 43-56 mph (70-90 kmph): 2d6 damage
* Speed 56-66 mph (90-107 kmph): 3d6 damage
* Speed 66-75 mph (107-121 kmph): 4d6 damage
* Speed 75-83 mph (121-134 kmph): 5d6 damage
* Speed 83-90 mph (134-145 kmph): 6d6 damage

and so on.

This suggests that any impact of 25+ mph is liable to kill a commoner more than half the time. That seems to tie in with the government statistics quoted on the web page. The web page, however, notes that the government statistics appear to have been made with the assumption of crash test dummies and psychotic drivers. That is certainly not the case in the real world. Thankfully for our purposes however, it is alarmingly often the case in an RPG, which makes their numbers useful for us.

Unfortunately, these numbers blatantly do not scale up appropriate for vehicles and typical vehicle hit point totals. This can of course be fixed by multiplying appropriately for the vehicle size (larger vehicles have less structural integrity, and are less able to withstand impacts).

----
Aside 1: How d20 Modern handles collisions
http://www.12tomidnight.com/d20modernsr ... hicles.php

The size of the damage die depends on the speed, and the number of damage dice depends on the size of the smallest object involved. A literal reading of these rules says that a naked human can run into a commoner, inflict 4d2 damage, and guarantee a kill :o
----
Aside 2: How GURPS handles collisions

damage inflicted by an object is based on (velocity x hit points), with velocity measured in yards/second, and hit points being typically 10 for a standard human. Falling has a special rule, in that damage is doubled if you fall onto a hard surface (such as most floors).

This makes a 10-yard fall "typically lethal", with a 50:50 chance of killing. Acrobatics skill can be used to reduce the effective distance fallen (similar to d20's Tumble/Jump skill usage).
----

Curiously, I seem to have adopted the same "physics" approach that GURPS uses, except that I use size class as a multiplier on damage inflicted, rather than using hp to measure mass, as GURPS does. Each size class larger adds the base damage once more (x2 for Large, x3 for Huge, etc.), and each size class smaller divides the base damage (/2 for Small, /3 for next size class down, etc.).

In order to account for the GURPS assumption that a collision is equivalent to falling on a soft surface, vehicle damage should be halved.

This is all getting rather complicated. Making I should rethink this.

Worked example: Human (medium size) gets hit by a car (huge size) moving at 50 mph. That's a base 2d6 damage. The human inflicts that much damage on the car, because he is medium size. the car inflicts 6d6 damage (x3) on the human, because it is two size classes larger than the base value. That's 6d6 damage. No commoner is going to survive that, and even heroes are in for ouch time.
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Re: [d20a] Falling

Postby Bonetti » Mon Sep 21, 2009 9:05 pm

I will have to admit I was always partial to the rule update in some very early Dragon magazine: 1d6 per 10' for every 10' fallen, which was supposedly the original AD&D rule (before an editor deemed it redundant and simplified it). This means 1d6 at 10', 3d6 at 20' (1d6 + 2d6), 6d6 at 30' (1d6 + 2d6 + 3d6), etc.

I think I liked it because it kept higher-level characters from jumping off cliffs to escape stuff :-)
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Re: [d20a] Falling

Postby Hugin » Mon Sep 21, 2009 9:08 pm

Bonetti wrote:This means 1d6 at 10', 3d6 at 20' (1d6 + 2d6), 6d6 at 30' (1d6 + 2d6 + 3d6), etc.

I think I liked it because it kept higher-level characters from jumping off cliffs to escape stuff :-)

Gives the sense of acceleration too! I like it.
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Re: [d20a] Falling

Postby Ashtagon » Wed Sep 23, 2009 9:46 am

More on Falling:

The GURPS formula makes falling damage proportional to the square root of the distance.

http://www.avsec.com/interviews/vesna-vulovic.htm

In game terms, she spent an action point to survive that fall. Judging from the number in the final paragraphs, despite gravity being 9.8 m/s2, a human body doesn't accelerate that fast.

Actual experimental data about fall survivability is, perhaps not surprisingly, hard to find.

http://www.cdc.gov/niosh/topics/falls/

* On September 5, 1992, a 45-year-old masonry worker fell 50 feet to his death from a scaffold in New York.
* On September 8, 1992, a 34-year-old painter plunged 364 feet from a bridge in Pennsylvania when a scaffolding cable broke. He was killed instantly.
* On October 2, 1992, two bricklayers, age 35 years and 50 years, fell 47 feet to their deaths when the plywood on their scaffold gave way at a construction site in Missouri.
* On October 27, 1992, a construction worker fell 13 feet when a scaffold collapsed in North Dakota. Fortunately, he was wearing a safety harness which prevented serious injury.
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Re: [d20a] Falling

Postby Blacky the Blackball » Wed Sep 23, 2009 11:52 am

I don't think that realism is the way to go with this. Trying to decide exactly how likely you are to die from falls of different distances and adjusting the falling damage accordingly is like trying to find out how likely you are to die from a getting sword through the head versus an axe in the head in order to work out weapon damage.

Basically, when it comes to falling in the real world, what you land on and how you land is much more important than how far you fell. You can fall 10' from a ladder and land on your head on jagged rocks and die, or you can fall 10,000' from an aeroplane without a parachute and survive because you landed on a snowy slope covered trees.

So I think that falling damage should be covered by the Rule of Cool and the Rule of Drama.

Do you want concealed pit traps to be a danger rather than an inconvenience? Then make falling damage big.

Do you want characters to be able to heroically jump out of high windows and land in conveniently placed haystacks? Then make falling damage small.

But I don't think any attempt to realistically model falling damage using hit points is going to work alongside D&D's fairly arbitrary hit-point system where damage that is guaranteed to kill a peasant can be shrugged off by someone with fighting experience even though the damage is unrelated to fighting expertise.
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Re: [d20a] Falling

Postby Gawain_VIII » Wed Sep 23, 2009 11:59 am

I'm with Blacky on this one. In the end, the fun of the game is paramount, seconded only by the drama of the story.

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Re: [d20a] Falling

Postby Ashtagon » Wed Sep 23, 2009 12:30 pm

My primary concern with the overall project is to be able to play a game that looks and feels realistic. Creating cinematic is easy - just pull some numbers out of a hat. The only question is how cinematic is that. 1d6 per 10 feet is plainly cinematic once you hit 40 foot falls, even for a 3rd level hero. 1d6 per 5 feet? per 20 feet? Hard to say. There's no objective scale to judge how much a cinematic fall hurts.

There is, however, an objective scale (albeit untested by extensive experimental data) on how much a realistic fall hurts. And it happens to be quite easy to modify a realistic set of rules to deal cinematic damage. It is a lot harder to modify a cinematic rule to realistic levels. That's why the base rules assumptions I am writing are for realistic injuries.
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Re: [d20a] Falling

Postby Ashtagon » Sat Feb 27, 2010 6:12 pm

Update on first post:

I streamlined the saving throw for mitigating Dex damage and the skill check for planned falls/dives. Aside from damage dice, there should now be a single skill/save check if you are making a planned fall/dive, plus a single Fort save to mitigate Dex damage and avoid being stunned.

I also changed the "converts one die to a single point" to "completely negates one die". That one point just seemed too petty.
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Re: [d20a] Falling

Postby rabindranath72 » Tue Apr 13, 2010 11:59 am

Bonetti wrote:I will have to admit I was always partial to the rule update in some very early Dragon magazine: 1d6 per 10' for every 10' fallen, which was supposedly the original AD&D rule (before an editor deemed it redundant and simplified it). This means 1d6 at 10', 3d6 at 20' (1d6 + 2d6), 6d6 at 30' (1d6 + 2d6 + 3d6), etc.

I think I liked it because it kept higher-level characters from jumping off cliffs to escape stuff :-)

This is what I use, too (Castles & Crusades has the same rule). It's realistic enough, yet it does not automatically implies death even for high level characters (which are in the realm of Wuxia anyway).
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Re: [d20a] Falling

Postby Ashtagon » Fri Jan 18, 2013 7:28 am

Relevant link is relevant: http://what-if.xkcd.com/28/
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