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View Full Version : D20 vs D100 for a Sci-fi Game?



Soft Serve
12-23-2009, 02:18 AM
For a lightcore Sci-Fi game how do you feel on D20 vs D100?

The only arguement I've seen was all about probability, but I'm wondering how you guys feel on how it effects Attributes and Skills and the like.

TAROT
12-23-2009, 09:54 PM
Is Lightcore a setting? When I Google, all I get is fibreoptics.

I don't understand what dice have to do with genre/setting.

Soft Serve
12-26-2009, 02:26 PM
Lightcore being the opposite of Hardcore.

As in Traveller to me is a Hardcore Sci-Fi setting because it's super in tune with the mathmatical aspects of the game. Like how fast your ship goes after however long of acceleration and the entire construction and creation process is very complex. (not that it's bad, but it's not what I want.)

Lightcore being I would only ever try to figure that out if I absolutely had too.

Webhead
12-26-2009, 03:07 PM
Which game systems are you considering using?

Soft Serve
12-26-2009, 03:09 PM
I'm not. I want to make my own.

Webhead
12-26-2009, 03:17 PM
Ah, I see. In that case, I think it's entirely based on your familiarity with such systems. If you know d20-based systems really well and can thus manipulate, extrapolate and gauge the "feel" of such a system, I would go that direction. Likewise for percentile systems.

Richard Littles
12-26-2009, 04:03 PM
I'd say neither and use a 3d6 based system since both d20 and d100 are linear die rolls. Characters will fail more often using a linear system then with a bell curve system.

outrider
12-26-2009, 04:54 PM
I agree with richard. It depends on what you are trying to accomplish. A bell curve will give more reliable results than a linear system.

Soft Serve
12-26-2009, 11:11 PM
Bell Curve?

I know the average of D6 rolls is like 3.5, but if that's the case wouldn't a D100's average be about 50-50.5 or so? In which case...what's the difference?

Richard Littles
12-27-2009, 12:05 AM
Bell Curve?

I know the average of D6 rolls is like 3.5, but if that's the case wouldn't a D100's average be about 50-50.5 or so? In which case...what's the difference?

A bell curve is the probabilities of hitting a specific total on 3d6 (or other multiple dice). For example, to roll an 11 is a 62.5% probability since there are three dice in play and the odds are in your favor that you will end up getting an 11 as a total 62.5% of the time since 11 is the mean for distribution. A roll of 3 and 18 sits at the extreme ends of the distribution of die rolls and occupy a .46% chance of a person rolling 3 1's or 3 6's. This means that on average a character's skills etc... will work reliably with a small percentage chance of them getting a critical failure or success. Positive modifiers are used sparingly because a single +1 can represent anywhere between 6%-16% chance on 3d6.

For a d20, each side of the die has an equal chance of showing up which is a flat 5%. Thus, the die rolls are very wild in their distribution where you will get critical failures, critical successes, normal failures, and normal successes equally. This leads to skills and other character abilities to be very unreliable. This is why d20 based systems use a lot of positive modifiers to boost the character's probabilities up to 63% because without them it's a very frustrating thing to sit through miss, miss, miss, miss, hit, miss, hit, hit, miss, etc.... A modifier in d20 is a flat 5% and at higher levels of the game there is the modifiers being outrageous like a +5 sword etc... The sword grants a +25% chance to hit itself.

The d100 has a 1% chance for any side to show up. It is far more granular in the distribution over d20, but it suffers from the same fickleness with probability regarding successes and failures as d20. Like the d20, depending upon how the system is written can pile on a lot of modifiers to give a character a reasonable chance to perform anything successful.

In Dark Heresy, a starting character will have on average a 30% in skills and they would routinely fail their rolls if there wasn't a rule in the book that said that all rolls for standard tasks are doubled. What this means is that for a standard task, a character's roll is 60% or less instead of 30% or less. For easier tasks the skill roll is multiplied repeatedly for each step it becomes easier.

If you were to compare starting characters between Dark Heresy, D&D, Fantasy Hero, and GURPS Fantasy you will find that the first level characters in D&D and Dark Heresy are totally incompetent in what they can do since the base chance of success is right around 30%. Contrast this a 75 point character in GURPS Fantasy and Fantasy Hero, the characters are totally competent in what they can do due to their base chance of success is at 62.5% for an 11 or less roll. Most characters in Fantasy Hero and GURPS Fantasy have at start a 13 or less roll in most skills which means they will be successful 83.8% of the time. Keep in mind that this is for standard tasks without any difficulty.

Soft Serve
12-27-2009, 12:31 AM
Then why is that preferred? It seems like after you become successful at something there's no real need to roll for it since there is such a small window for error.

Richard Littles
12-27-2009, 12:41 AM
Then why is that preferred? It seems like after you become successful at something there's no real need to roll for it since there is such a small window for error.

It comes down to the philosophy of a person is competent and knows their job, but fate can be fickle. In a 3d6 system, modifiers play an important role since each +/-1 can represent 6%-16% chance on a roll. Yes, a character may be very competent with standard tasks, but factors like range, difficulty, etc... can impede a character. You'll also use a lot less modifiers when running a game, but when you do they can make or break any character. Also, opposed tests of skill are the deciding factor.

In my playtest games, people have found that they can reliably do something, but things that most games don't touch upon actually impact their performance. They know that they can survive in combat as long as they don't do anything stupid and they can do things without worrying about having to fail all the time.

It ultimately comes down to whether you feel that heroes should be heroic and reasonably succeed most of the time or you think they should incompetent sidekicks that die during the most mundane tasks.

Soft Serve
12-27-2009, 01:04 AM
It comes down to the philosophy of a person is competent and knows their job, but fate can be fickle. In a 3d6 system, modifiers play an important role since each +/-1 can represent 6%-16% chance on a roll. Yes, a character may be very competent with standard tasks, but factors like range, difficulty, etc... can impede a character. You'll also use a lot less modifiers when running a game, but when you do they can make or break any character. Also, opposed tests of skill are the deciding factor.

In my playtest games, people have found that they can reliably do something, but things that most games don't touch upon actually impact their performance. They know that they can survive in combat as long as they don't do anything stupid and they can do things without worrying about having to fail all the time.

It ultimately comes down to whether you feel that heroes should be heroic and reasonably succeed most of the time or you think they should incompetent sidekicks that die during the most mundane tasks.


I like deadly games in general. Games where the character generation is short and sweet because if you need to make a new one you can in about 7 minutes if you know the ins and outs.

Richard Littles
12-27-2009, 01:08 AM
I like deadly games in general. Games where the character generation is short and sweet because if you need to make a new one you can in about 7 minutes if you know the ins and outs.

And what kind of story can you tell when all the characters die in 5 minutes of game time? One of the things that I really hated about Cyberpunk 2020 was that you could die from the smallest of bullets without much recourse. Sure the character creation was quick, but the stories usually ended up being one shots and people got bored with character creation. To me the essence of a role playing game is to tell a story and if the characters survive (ie are competent) then the story will continue on without fear of there being a premature end. It's hard to tell a full story when the entire cast is dead.

Soft Serve
12-27-2009, 01:32 AM
I didn't say the characters did die every 14 seconds or so, but with a little element of luck and the intelligence to not make stupid moves they stay alive usually. Character deaths in the games I make like that usually fall under bad rolls, bad teamwork, or horrible communication.

Richard Littles
12-27-2009, 01:44 AM
I didn't say the characters did die every 14 seconds or so, but with a little element of luck and the intelligence to not make stupid moves they stay alive usually. Character deaths in the games I make like that usually fall under bad rolls, bad teamwork, or horrible communication.

Character deaths in my games are the result of a good storyline and if the player wishes it to happen. I bring my players to the edge and make them sweat on whether their characters will survive, but I will not kill them even when there is a bad die roll. However, this doesn't address the whether you like competent or incompetent characters.

Soft Serve
12-27-2009, 01:49 AM
Depends on what you consider competent.

A soldier in the U.S.M.C. can die in one shot. That doesn't make him incompetent.

Richard Littles
12-27-2009, 02:15 AM
Depends on what you consider competent.

A soldier in the U.S.M.C. can die in one shot. That doesn't make him incompetent.

A solider in the USMC will be able to hit targets out to 250m reliably, but a USMC using d20 or d100 is so bad at hitting that he would have washed out of boot.

Soft Serve
12-27-2009, 02:17 AM
A solider in the USMC will be able to hit targets out to 250m reliably, but a USMC using d20 or d100 is so bad at hitting that he would have washed out of boot.


Good point.

Alright Rich I think I'll settle on 3D6. I haven't done it yet, and I might as well experience it. I hope you know though I'm coming to you with any questions. :lol:.


Thanks everyone, if you think you have any better ideas go ahead and keep posting.

templeorder
12-27-2009, 11:17 AM
D20 goes in jumps of 5% probability. Its easy to conceptualize. D100 has varying adaptations. These can be linear or random in progression. Only Star Frontiers used a more interesting approach which had a learning curve i really liked. In the end, its matters most about flavor and which system suits best. I find D20 does not suit me. I really only play my own Incarna system any more, but i play sci-fi, western, fantasy - all genres. I prefer d100 for the flavor. And D100 tend too to use less dice (tend, not all) - i prefer less dice.

Dytrrnikl
12-27-2009, 01:07 PM
Maybe it's due to my experiences with FASA Star Trek, d100 system, I am a fan of percentile systems and opposed rolls for ALL Sci-fi light- or hard- core. Although after reading Rich Littles support for 3d6, I'm inclined to agre with him. I do prefer more lethal games though as well, as it is not uncommon for player's in my games to have at least two characters, sometimes three throuhgout the course of a campaign.

Soft Serve
12-27-2009, 06:27 PM
Maybe it's due to my experiences with FASA Star Trek, d100 system, I am a fan of percentile systems and opposed rolls for ALL Sci-fi light- or hard- core. Although after reading Rich Littles support for 3d6, I'm inclined to agre with him. I do prefer more lethal games though as well, as it is not uncommon for player's in my games to have at least two characters, sometimes three throuhgout the course of a campaign.


Same on about everything you said. I haven't tried 3D6 yet so if I find it's either too difficult or someone talks me out of it I think I'll try it on.

michael
12-27-2009, 07:16 PM
http://www.thedarkfortress.co.uk/tech_reports/tech_assets/3-dice-charts.gif

Frobozz
12-28-2009, 03:05 PM
Reminds me of 1st edition AD&D. The Tomb of Horrors - a module where you'll probably go through 4 characters before you make it to the demilich at the end.

Personally, I like d20 and Palladium game systems for things like Sci-Fi. Palladium is heavy on the skills, but has pretty good rules for guns and vehicles. d20 is easier creation wise, but just doesn't seem to handle tech well, even when using d20 Modern/Sci-Fi.

You could also go the Feng Shui route and make an ultra-light game system where except for simple combat rolls, all decisions are made by the GM and players.

There's a lot of statistics in order to make a decent game engine. It all depends on how close to real life and how detailed you want your mechanics.

Not to say there aren't flawed systems out there. White Wolf's system (at least, the one they used in the 90's last I played with it) broke down when you tried to roll against a target number 10 because rolling a 10 gave you a success, but it forced you to reroll, which increased your chance of getting a 1 and thus, cancelling out your success.

Shadowrun 3rd edition had probability curves that had "steps" in them because a target number 6 and 7 were statistically the same thing (when you rolled a 6 on a dice, you re-rolled and added the second roll to it, since you were always rolling 1 or higher, a TN7 was no different from a TN6), same with 12 and 13 and on up.

Soft Serve
12-29-2009, 01:31 AM
http://www.thedarkfortress.co.uk/tech_reports/tech_assets/3-dice-charts.gif

Really? :rolleyes:


Reminds me of 1st edition AD&D. The Tomb of Horrors - a module where you'll probably go through 4 characters before you make it to the demilich at the end.

Personally, I like d20 and Palladium game systems for things like Sci-Fi. Palladium is heavy on the skills, but has pretty good rules for guns and vehicles. d20 is easier creation wise, but just doesn't seem to handle tech well, even when using d20 Modern/Sci-Fi.

You could also go the Feng Shui route and make an ultra-light game system where except for simple combat rolls, all decisions are made by the GM and players.

There's a lot of statistics in order to make a decent game engine. It all depends on how close to real life and how detailed you want your mechanics.

Not to say there aren't flawed systems out there. White Wolf's system (at least, the one they used in the 90's last I played with it) broke down when you tried to roll against a target number 10 because rolling a 10 gave you a success, but it forced you to reroll, which increased your chance of getting a 1 and thus, cancelling out your success.

Shadowrun 3rd edition had probability curves that had "steps" in them because a target number 6 and 7 were statistically the same thing (when you rolled a 6 on a dice, you re-rolled and added the second roll to it, since you were always rolling 1 or higher, a TN7 was no different from a TN6), same with 12 and 13 and on up.

I realized that when I played too and quickly removed any re-rolls from hitting perfect #'s in any game I made.

My problem with D20 is that it's too small. 1-20 doesn't feel like enough for me especially if I want a specific TN. Also I bet we could name 50+ d20 based games and I'd rather divorce myself from that whole trend.

D100 delivers on that scale, but it becomes more difficult to accurately judge how much to reward players modification wise. +10 seems too small, but +20 seems too much. +15 seems complicated...Other than that though this has to be my number one choice at the moment. (backing out of my earlier 3d6 decision for the following reason...)

3D6 being 3-18 also sounds complicated. It also seems to be completely out there as far as modifications go. (+3 being a fairly high mod in this case.) And is also completely alien to me. I am interested in the Bell Curve deal we went over in the thread earlier but now I'm back to teeter-totting only I now have 3 options...

On top of it all I'm trying to think of what a three way Teeter-Totter looks like...

:confused:

Richard Littles
12-29-2009, 02:24 AM
Really? :rolleyes:



I realized that when I played too and quickly removed any re-rolls from hitting perfect #'s in any game I made.

My problem with D20 is that it's too small. 1-20 doesn't feel like enough for me especially if I want a specific TN. Also I bet we could name 50+ d20 based games and I'd rather divorce myself from that whole trend.

D100 delivers on that scale, but it becomes more difficult to accurately judge how much to reward players modification wise. +10 seems too small, but +20 seems too much. +15 seems complicated...Other than that though this has to be my number one choice at the moment. (backing out of my earlier 3d6 decision for the following reason...)

3D6 being 3-18 also sounds complicated. It also seems to be completely out there as far as modifications go. (+3 being a fairly high mod in this case.) And is also completely alien to me. I am interested in the Bell Curve deal we went over in the thread earlier but now I'm back to teeter-totting only I now have 3 options...

On top of it all I'm trying to think of what a three way Teeter-Totter looks like...

:confused:

To give you an idea of how 3d6 would operate go and download the GURPS Lite here. (http://www.sjgames.com/gurps/lite/) This way you can see how it works and get experience with it. GURPS Lite is completely free.

Soft Serve
12-29-2009, 02:28 AM
Can't download on work computer...I would any other day though.

Richard Littles
12-29-2009, 02:36 AM
Can't download on work computer...I would any other day though.

Well, download it when you get home to your computer. ;)

Soft Serve
12-29-2009, 02:58 AM
Well, download it when you get home to your computer. ;)


Lol it's broken...And not connected to the internet.

Law Dog
12-29-2009, 11:12 AM
I'd say neither and use a 3d6 based system since both d20 and d100 are linear die rolls. Characters will fail more often using a linear system then with a bell curve system.


Depends on the system and how high the stats/checks are.

You can represent the same % chance of success or failure in both systems. A 10 or less 3d6, an 11 or more 3d6 and a 50% over or under are all essentially the same rolls.

michael
12-29-2009, 01:14 PM
http://www.thedarkfortress.co.uk/tech_reports/tech_assets/3-dice-charts.gif


http://www.penandpapergames.com/forums/picture.php?albumid=252&pictureid=1479

Richard Littles
12-29-2009, 04:23 PM
I like this breakdown (http://catlikecoding.com/anydice/?dice=3d6) a lot better. It gives the overall percentages for each of the possible rolls starting with 3 then goes up to 18.

Soft Serve
01-01-2010, 12:54 AM
I like this breakdown (http://catlikecoding.com/anydice/?dice=3d6) a lot better. It gives the overall percentages for each of the possible rolls starting with 3 then goes up to 18.


That is insane. I'm taking D100 because I like the wide number of possible rolls, and the ability to make more diverse opposed checks.

Dytrrnikl
01-01-2010, 02:11 PM
Soft Serve

I was just looking through the FASA Star Trek system - Game Operations Manual. Here is a condensed break down of what they felt d100 seemed to indicate:

UNSKILLED - 0 rating. Basically, you just can't do it.

SEMISKILLED - 1% - 9% rating. Roll 1d10 to determine success or failure for any routine use of the skill. Slim to no chance of success of being able to pull something off under critical circumstances withthis skill.

QUALIFIED - 10% - 39% rating. Pretty much succeed with skills at this rating range for all non-critical, routine or leisurely tasks. It's not a awesome success, jsut proficient enough to get the job done.
Physical Skills - Every 10 points in the skill gives you a degree of success for normal, noncritical and leisurely actions. SO that a character with a rating of 30 would perform the skill 3 times better than someone with a rating of 10 and take less time to do it.
Mental Skills - rating 10 means you know most common facts and can use skill successfully to solve problems in noncritical leisurely situations. The higher the skill rating in mental skills indicates teh quality of the solution, difficulty of solution able to be solved, and tiem needed.

PROFESSIONAL - 40% - 79% higher rating. Creditable success in noncritical situations (no fear of failure). reasonable chance of success in critical situations.

EXPERTS - 80% or hihger rating. Good chance of success even in most critical situations, though even experts may still fail tasks during critical situations.

Of course rolling 100 is auto failure and rolling 1 is auto success. AND noncritical means you don't really need to roll to determine success.

michael
01-01-2010, 06:17 PM
I like this breakdown (http://catlikecoding.com/anydice/?dice=3d6) a lot better. It gives the overall percentages for each of the possible rolls starting with 3 then goes up to 18.

That site kicks butt!

Soft Serve
01-01-2010, 07:40 PM
When I figure out how I'm going to use the D100 I'll put it here too...lol.
--- Merged from Double Post ---
Also if anyone has any suggestions or would like to help in my endeavor to make this feel free to pitch in.

michael
01-02-2010, 09:50 PM
I like to percentile system (albeit not as much as 3d6) because it is a very intuitive thing to describe a PCs chance of success as a percentage.

Do you have a baseline scope set up for the campaign yet? Is it planetary? ship-based? System-wide? FTL? Galactic or Universal? Time and dimension jumps? do you have different races designed or chosen? Tech levels? Are you going to allow psionics? Magic? Magic the Gathering? (Black Lotus ftw!)

Who are the major villains? Any NPC heroes? What about resource levels? Do the men of Northern cumberlain prefer shoes with silver buckles?

Soft Serve
01-02-2010, 10:10 PM
I like to percentile system (albeit not as much as 3d6) because it is a very intuitive thing to describe a PCs chance of success as a percentage.

Do you have a baseline scope set up for the campaign yet? Is it planetary? ship-based? System-wide? FTL? Galactic or Universal? Time and dimension jumps? do you have different races designed or chosen? Tech levels? Are you going to allow psionics? Magic? Magic the Gathering? (Black Lotus ftw!)

Who are the major villains? Any NPC heroes? What about resource levels? Do the men of Northern cumberlain prefer shoes with silver buckles?

Yes, ish, no, idk, what's the difference? Neither, just humans, one basic tech level, no psionics, or magic, or magic the gathering.

I haven't decided yet, yes, not sure yet, They probably do.

Frobozz
01-04-2010, 05:18 PM
Planetary = Only takes place on a single planet and/or it's moons, orbiting stations, etc. 2001 a Space Odyssey, Bubblegum Crisis and the world of William Gibson's Neuromancer are examples of this.

Ship-based = Ships and ship ownership plays a major part in the campaign; as opposed to players always booking passage on NPC ships or shuttle service.

System-wide = Only takes place within a single solar-system and all planets, moons and stations thereof. Classic sci-fi and anime that are only System-wide include 2010, Mission to Mars, Total Recall, Macross, Martian Successor Nadesico.

FTL = Faster-than-light travel; i.e: Breaking relativity's laws. Do ships in your game adhere to the laws of relativity? At light-speed, it takes 4 hours to fly to Neptune and years to reach nearby stars; this is without any relativistic effects on aging (at near the speed of light, you age much slower than everyone else). The "Ender's Game" novels by Orson Scott Card is an example of sci-fi that strictly adhered to non-FTL travel. Most classic sci-fi use FTL either in the form of hyperspace (Star Wars), space warping (Star Trek), or jump-drives (Battlestar Galactica).

Galactic = Takes place within a single galaxy or section thereof. Most classic sci-fi fit this category including Star Wars, Star Trek and Battlestar Galactica.

Universal = Even the galactic threshold has been breached and travel between galaxies is possible (and now we're talking REALLY huge distances!). Dr. Who is an example of this and so some degree Stargate SG1.

Time-travel = Is time travel possible? How does time travel work? A whole separate set of questions.

Dimension jumping = Are alternate dimension travel possible? How does this work? Another whole separate set of questions.

michael
01-05-2010, 11:18 AM
I am running a game now where the PCs had access to the whole system they were adventuring in, but a large war basically took that away from them. Now they are stuck on Earth, trying to help re-establish the Terran government from the hostile invaders that have co-opted many Earth-based power-brokers. Does that help Soft Serve?

Soft Serve
01-09-2010, 12:37 AM
http://www.penandpapergames.com/forums/showthread.php?t=14519 (http://www.penandpapergames.com/forums/showthread.php?t=14519)

Started a new thread as this one has changed subjects a little.