2d6 vs TN greater then 12

[jaz0nj4ckal]

3d6 is a closer fit to d20 in terms of span (16 range compared to 20 with the same centre). There's been some discussion over the years as to how well a 3d6 bell curve replaces a single d20 which you can find easily with google.

In a nutshell, it'll work, sort of. Secondary effects, like critical hit chances, and tertiary effects like the relative value +1 to AC become very different with a bell curve.

I would recommend a different approach though. Rather than picking a mechanic that is different then figuring out its effects, figure out what you want to accomplish then find a mechanic that maps to it.

Understand and thank you for your advice. Can you recommend a system or point me in the right direction? I want to use 2d6 or 3d6; however, I want to use a system like D&D, which has armor class from 0-10. The latter would apply penalties to the 2d6/3d6 dice roll. In addition, range would have penalties as well for stuff like: box, crossbows, dagger thrown, etc.

I do have Classic Traveller around; however, I want more bonuses/penalties due to armor and range. In addition, I want to model D&D levels as levels in skills, and not THAC0. Example: 2nd level fighter would have Skill Level 2 in Long Sword or whatever weapon the player selected as their primary.

I like rule light systems, which allows me to craft my own ad-hoc rules at the point in time during play. Due to the latter, that is why I like OD&D/D&D and Classic Traveller.


++laugh++ I really have not moved beyond 1995, RC edition of D&D and Gazetteer books. That should give you an idea of my style of play.

 

[aramis erak]

Hmmm I see what you are saying. Do you know what a good baseline or ballpark figure for TN numbers? Do you think they should scale with character skill levels?

I am imagining a system that is very similar to Classic Traveller; however, with higher TN due to different Armor classes and +/- weapons. Sort of in a way - I want to transition D&D/OD&D to use 2d6 dice rolls to keep things simple and use only d6 dice.

Trying to get a OD&D/D&D feel with (2d6+skill+bonus/pen => TN); however, I am not sure where to start with TN values.

NOTE - TN values will be anything built from Armor class and range modifiers.

Typical ranges depend upon system, however...

Some 2d6 systems for your consideration

CT: 2d6, 8+, sometimes 11+, skills typically add between 0 and 4. Attributes ±1, Conditional mods all the way to ±15 or so (due to cumulative mods).
MT: 2d6 3+/7+/11+/15+/19+, Attributes add 0-3, skills add 0-5 (max +8 between two assets). Unskilled DM-4
MGT: 2d6, 8+, stat –3 to +3, skill +0-4, difficulty ±6, conditional mods ±6 or more. Unskilled DM -3.
D-Trek: 2d6 (12=+1d6) 5+/10+/15+/20+/25+ addtributes range from -3 to +6 (for human range), skills add 0-12 (starting PC's often have skills of +3 to +5 in key fields)
In MT, MGT, and D-Trek, the lowest is labeled simple or routine, and the highest (nearly) Impossible,
Battletech/Mechwarrior 2d6 for 6–, skills can raise this to 12– or higher, modifiers for situation and difficulty.

 

[tomBitonti]

A key difference between a uniform distribution (d20) and one with multiple dice (3d6) is that a +1 bonus has a different meaning depending on the target number.

On a d20, +1 always has the effect of increasing the expected outcome by 5%. For example, if you do 10 points of damage on average on a successful hit, with a target of 11 on a d20 your expected damage is 5 (50% of 10). A +1 increases the expected damage to 5.5 (55% of 10, from a modified target number of 10, or 11 out of 20.)

The same +1 on a 3d6 roll has a very small effect with either a low or high target number, and a larger effect for middle numbers. For example, a target of 5 on a 3d6, which is met except on a 3 or a 4, has a 212 out 216 chance of success. Changing the target to a 4 makes the chance 215/216, a difference of just 3/216, quite a bit less than 10-11/216, which is the close approximation of 5%.

(I'm setting aside special results on fixed die rolls, say, criticals on a 20 on a d20 or 18 on a 3d6.)

What is best is to play with the numbers a bit to get a feel for how the results change.

Edit: Here is a nice discussion on rolling 3d6:

http://www.thedarkfortress.co.uk/tech_reports/3_dice_rolls.htm#.WC0NiLQ8KfA

They also have nice discussions for rolling 2d6 and 4d6. Navigate from the posted link to find these discussions.

An interesting idea is to replace d20 with 4d6-4. The ranges changes from 1-20 to 0-20. Or, 4d6-3, which has a range of 1-21.

A problem of rolling 4d6 can be waiting for folks to add their dice. Some folks do the addition in an instant. But not everyone!

Thx!
TomB

 

[jaz0nj4ckal]

CT: 2d6, 8+, sometimes 11+, skills typically add between 0 and 4. Attributes ±1, Conditional mods all the way to ±15 or so (due to cumulative mods)

Cumulative mods is something I a looking for in the system with the TN. For example: target is wearing some sort of chain armor AC4 (-4) and is sort range (-2), so the TN becomes 13; however, is that a good way to view the mechanics? If I do a direct drop in to D&D, with 11 different AC (0-10) then I am at a lost as to how to simulate this on a 2d6 dice roll. I guess I could use 3d6; however, I believe that has other issues.

In addition, I am doing something along the lines of: each THAC0 change is translated as a skill level to primary weapon. So, if we use the Fighter as example:
L1 = 0
L2 = 1
L3 = 2
L4 = 3
~

The fighter will always be Skill level in primary weapon -1 his level.

 

[aramis erak]

Ok, so you've got a basic idea what you're doing. What level range are you looking to support?

I'm going to expand a bit on CT combat just to make certain you've got a good grip on what CT's 8+/11+ model is...

In CT bk 1 combat... the combined armor and range mods range from –8 to +16; adding Bk 4's additional weapons changes it to –16 to +16.
Attributes provide either a –1 or –2 for low att, and a +1 or +2 for high att.
Drawing is a –3.
Shooting in the dark is –9 past short range, and –6 for partial darkness (moonlight, starlight)
Evading is –1 at shor, -2 at medium, –3 at long or longer
target has fired from Cover -4; target in cover - hit the cover.
Concealment –1

But what do those mean? 8+ is 15/36 A DM –4 makes it 1/36 (figured as 8–(–4)=12; 12+ is 1/36)
So, your level 1 fighter, with skill = level–1 = 0...
At short range, can hit an unarmored target with a baseball/cricket bat or a walther pretty much about 15/36=5/12 of the time. If they're being "evasive", that's dropped (DM-1) to 10/36 = 5/18.
At night, he can't hit at all; he needs 8+ with a DM–6, so he needs a 14+ on the raw dice... can't be done.

At 6th level, same weapons
he's almost unable to miss a non-evading target in daylight at short range. An 8+, with a DM+5, is a 3+ natural roll needed; 35/36.
At night, he can shoot the guy with a natural 9+, for 10/36...

At 10th level, he can ignore total darkness, and can hit evading targets unerringly in the daytime.

Using 2d6, you're dwarfing the dice with skill mods alone. A 20th level fighter isn't going to miss even with the worst case. With Traveller's limited range of skill (0-5, attribute ±2), of -6 (unskilled and bad attribtue ) to +7 (skill 5 and good attribute), it's possible to swamp the dice with the mods, and that's a huge complaint about CT.

Striker & AHL simplified combat dice 8+, 10+ and 12+ by weapon's range bands 8+ to effective, 10+ to long, and 12+ to extreme.
DM+ skill (with 3 being elite, counting both att and skill level; PC's can hit +7 as for CT standard).
Cover -1
Evasion -1
Autofire +4/+3/+1 by range

Much narrower range of modifiers, much easier to play. But PC skills can totally swamp the system - Skill 5 rifle with +1 from high dex, in autofire... he's got +8 on that 12+, so needs a 4+ on the dice... 33/36, or 11/12 hit chance. He can't miss at all at effective range; the 8+ is swamped by his +6 to be 2+.

If you're going to have a system using 2d6, you probably do not want to have skill exceed "base target number –3" ... because, if you do, then you either need either a minimum miss chance (and 1/36 is not a good one - too steep) and a minimum success chance (again, 1/36 is too much), or need to allow open ending on the dice (EG: Nat 2, reroll at further –8; nat 12 reroll at +8), or some other adjustment.

 

[jaz0nj4ckal]

Ok, so you've got a basic idea what you're doing. What level range are you looking to support?

I'm going to expand a bit on CT combat just to make certain you've got a good grip on what CT's 8+/11+ model is...

In CT bk 1 combat... the combined armor and range mods range from –8 to +16; adding Bk 4's additional weapons changes it to –16 to +16.
Attributes provide either a –1 or –2 for low att, and a +1 or +2 for high att.
Drawing is a –3.
Shooting in the dark is –9 past short range, and –6 for partial darkness (moonlight, starlight)
Evading is –1 at shor, -2 at medium, –3 at long or longer
target has fired from Cover -4; target in cover - hit the cover.
Concealment –1

But what do those mean? 8+ is 15/36 A DM –4 makes it 1/36 (figured as 8–(–4)=12; 12+ is 1/36)
So, your level 1 fighter, with skill = level–1 = 0...
At short range, can hit an unarmored target with a baseball/cricket bat or a walther pretty much about 15/36=5/12 of the time. If they're being "evasive", that's dropped (DM-1) to 10/36 = 5/18.
At night, he can't hit at all; he needs 8+ with a DM–6, so he needs a 14+ on the raw dice... can't be done.

At 6th level, same weapons
he's almost unable to miss a non-evading target in daylight at short range. An 8+, with a DM+5, is a 3+ natural roll needed; 35/36.
At night, he can shoot the guy with a natural 9+, for 10/36...

At 10th level, he can ignore total darkness, and can hit evading targets unerringly in the daytime.

Using 2d6, you're dwarfing the dice with skill mods alone. A 20th level fighter isn't going to miss even with the worst case. With Traveller's limited range of skill (0-5, attribute ±2), of -6 (unskilled and bad attribtue ) to +7 (skill 5 and good attribute), it's possible to swamp the dice with the mods, and that's a huge complaint about CT.

Striker & AHL simplified combat dice 8+, 10+ and 12+ by weapon's range bands 8+ to effective, 10+ to long, and 12+ to extreme.
DM+ skill (with 3 being elite, counting both att and skill level; PC's can hit +7 as for CT standard).
Cover -1
Evasion -1
Autofire +4/+3/+1 by range

Much narrower range of modifiers, much easier to play. But PC skills can totally swamp the system - Skill 5 rifle with +1 from high dex, in autofire... he's got +8 on that 12+, so needs a 4+ on the dice... 33/36, or 11/12 hit chance. He can't miss at all at effective range; the 8+ is swamped by his +6 to be 2+.

If you're going to have a system using 2d6, you probably do not want to have skill exceed "base target number –3" ... because, if you do, then you either need either a minimum miss chance (and 1/36 is not a good one - too steep) and a minimum success chance (again, 1/36 is too much), or need to allow open ending on the dice (EG: Nat 2, reroll at further –8; nat 12 reroll at +8), or some other adjustment.

Hmmm... thank you for such a detailed post. You make it sound like that I will have some problems with 2d6 system. I have not really played traveler in over 20 years, since I can never get anyone to play, so I am very rusty on Traveller rules, and can only remember the basics.

In your opinion, do you think it is better to do something like GURPS (ex. 3d6 under your skill score)? I am not a big GURP fan due to point buy, defense rolls and armor take away damage. Much rather have armor change the modifier to hit chance, so I can build an attack matrix table for weapon vs armor.

However, I have been looking into GURPS and Fighting Fantasy for ideas.

 

[aramis erak]

Hmmm... thank you for such a detailed post. You make it sound like that I will have some problems with 2d6 system. I have not really played traveler in over 20 years, since I can never get anyone to play, so I am very rusty on Traveller rules, and can only remember the basics.

In your opinion, do you think it is better to do something like GURPS (ex. 3d6 under your skill score)? I am not a big GURP fan due to point buy, defense rolls and armor take away damage. Much rather have armor change the modifier to hit chance, so I can build an attack matrix table for weapon vs armor.

However, I have been looking into GURPS and Fighting Fantasy for ideas.

2d6 works just fine... if, and only if, you set the difficulties correctly.

The MegaTraveller system works well for me - the +8 DM limit, and knowing that the difficulty labels are descriptive for "Stat 7 (+1 mod), Skill 1" - and only character side stuff modifies the roll (and falls into that +8 limit), while anything exterior to the character shifts the difficulty level (rather than being a modifier to the dice). It was fast, flexible, and, once learned by players, made tasks less intrusive into the flow of the game than CT's 8+ on 2d6+ManyManyMods...

Further, the "Impossible" (19+) level is impossible for the reference Skill-1 stat-7 character to accomplish... he's got a +2, and the extra time shift down one level still needs a 15+... which on 2d6+2, you can't do.

The big issues are
1) Mods make dice irrelevant
2) mos make a notable difference in outcomes

I'd say, coupling it to level–1 is going to be too much modifier for combat unless you add minimum miss chances; but in that case, 2d6 is almost too granular to use the Nat 2 always misses and nat 12 always hits; I find the nat 1/nat20 in d20 too common, too.

 

[jaz0nj4ckal]

Hmmm... don't believe I played MegaTraveller.

The MegaTraveller system works well for me - the +8 DM limit, and knowing that the difficulty labels are descriptive for "Stat 7 (+1 mod), Skill 1" - and only character side stuff modifies the roll (and falls into that +8 limit), while anything exterior to the character shifts the difficulty level (rather than being a modifier to the dice).

Can you give me an example if you don't mind, just so I have a rough understanding? I really liked the simplicity of the 2d6 dice roll.

Thank you

 

[aramis erak]

Megatraveller has 7 actual levels of difficulty, 5 with dice roll mechanics (and explicit call out in rules)...
All tasks are set up as 2d6 +AssetA +AssetB (optional ±2 for gear quality
An asset is either attribute÷5 (round down) or a skill (at full level).
Good gear adds +1 to the roll, bad -1.

Automatic - no roll
Simple 3+ on the roll
Routine 7+ on the roll
Difficult 11+ on the roll
Formidable 15+ on the roll
Impossible 19+ on the roll
Auto-fail - no roll.

On any roll, a nat 2 is a mishap - but may still succeed.
On any roll, a nat 12 succeeds.
Make or fail the roll by 2 or more for exceptional success/failure.
Halve the needed time, shift difficulty one harder.
Double the needed time, shift difficulty one easier.
if the situation makes things harder, shift difficulty one step harder; easier, one easier. Two shifts should be rare

So, let's take a basic task definition:

To shoot a guy at short range with a pistol: Routine, Dex, Pistol. 1 Action.​

Routine means 7+
Dex, being an attribute (on traveller's 1-15 attribute scale), is divided by 5. Policeman Joe Normal is Dex 7. So that's 7÷5=1
Pistol, being a skill, is added straight. He's a well trained shot - pistol 2.
So Joe needs a 7+ on 2d6+1 (from dex) and +2 (from skill), for a 2d6+3 total.
If he spends the turn prior aiming, it's one easier; 2d6+3 for 3+
If he draws and fires (shooting from the hit), it's harder - make it difficult 11+

To replace a broken Firing Pin: Simple, Mechanic, Pistol​

Improvised tools? Make it routine.
Missing either skill? Up one difficulty for each missing.
Rushing? Another difficulty
So, fixing it in a hurry with just a pocketknife and without being trained in mechanics? Joe's still rolling 2d6+3... but now needs Sim ↗︎ Rou (unskilled) ↗︎ Dif (Improvised tools) ↗︎ Form (rushing). Joe needs 15+ on 2d6+2 (his pistol skill)... he's going to fail. The question is how badly... he can get a marginal success on a nat 12 if the Ref lets him roll at all...

What's lost in granularity is made up for with handling speed.

Decipher Trek is substantially similar, but always uses one attribute and one skill, and open ends a 12 to 1d6+12, hence the higher difficulty TN's. (plus higher expected skill - the default is Att 7 gives +0 and skills in field usually start around 4.)
It also groups collections of direct situational modifiers to the base difficulty, which said difficulty is "Normal working conditions for that skill"... so only combat skills are presumed to be combat use...
It's not nearly as clean to run as MT...