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Author Topic: Exploding 2d6  (Read 2403 times)

Daryk

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Exploding 2d6
« on: 17 December 2016, 11:04:06 »
One complaint I've seen repeatedly about using 2d6 is that it offers too narrow a range of possibilities before becoming impossible to achieve a target number.  I don't recall seeing any threads about using the "exploding dice" method here (not that there aren't any), and worked through a couple of possibilities with a spread sheet.  I think using 9 as a start for post-12 target numbers works relatively well.  For example, a target number of 13 would require an initial roll of 12, and a secondary ("exploded") roll of 9 to achieve.  14 would need a 10, 15 an 11, and 16 a 12 on the secondary roll.  To get to a target of 17 would require two consecutive 12s followed by a 9, etc., etc.  This puts 13s beyond a 1-in-100 chance, 16s beyond 1-in-1,000, and 24 beyond 1-in-1,000,000.

Any links to previous discussions would be appreciated.

skiltao

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Re: Exploding 2d6
« Reply #1 on: 22 January 2017, 19:18:45 »
I've looked at dice odds a little bit before.

I guess the question here is, how often are the TNs climbing that high? Because if (for example) 1-in-10 TNs are 14+, then the dice had better roll 14+ more frequently than 1-in-100.

Your solution is interesting. It works if high TNs are relatively uncommon, so I might use it in an RPG, where rolls are pretty infrequent; but in regular tabletop BattleTech I think the extra confirmation roll might be too much overhead, and doesn't offer a lot over the similar "12s always hit, 2s always miss."

As far as I can tell, the only way to smoothly allow for infinitely increasing TNs is with a dice pool system like Shadowrun or World of Darkness or Betrayal at House on the Hill, but that would involve quite a lot more retooling.
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Daryk

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Re: Exploding 2d6
« Reply #2 on: 22 January 2017, 21:03:08 »
Very interesting link, thanks!  Your first method seems to "steal" probability space from the mid-low and mid-high numbers to make the extremes possible while keeping the middle spot on.  It's a neat idea, but I agree it's probably too fiddly for table top use.

As far as how often target numbers climb that high, I'll say it was very common back in college when we implemented the BattleTechnology extreme range rules.  Before our gunnery skills hit negative territory, we'd just stop counting at 13 and shrug our shoulders.

Cryhavok101

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Re: Exploding 2d6
« Reply #3 on: 23 January 2017, 09:18:06 »
It works if high TNs are relatively uncommon, so I might use it in an RPG,

Doesn't the RPG already use exploding dice?

(Just checked, it is on AToW pg 41, "Stunning Success and Miraculous Feats")

Daryk

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Re: Exploding 2d6
« Reply #4 on: 25 January 2017, 19:54:29 »
Honestly I'd missed that rule, but looking at it, I think it's likely still subject to the "too narrow" accusation. I'm dead set against a 1-in-36 chance of automatic failure.  That's a universe that doesn't work on a very fundamental level.

skiltao

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Re: Exploding 2d6
« Reply #5 on: 03 February 2017, 20:19:49 »
Thanks for pointing that out, Cryhavok101. I'd either forgotten it or never knew it.

I don't know if I'd call exploding dice too narrow in an RPG environment. In its simplest form ("see maximum roll, add bonus dice") it isn't much overhead; and if low and middle Target Numbers can benefit from increased margins of success, or if PCs can attempt difficult tasks (e.g., trying to forge the finest sword in the realm, or trying to suss out an NPC's background and allegiances based on their dialect and diction) without failure being too costly, then I think they have broad enough use.

On the other hand, if the characters regularly get attacked by units too fast, stealthy or distant to defeat (or escape) and the only way to be competitive is to roll explodingly high, then that's when I'd say they're too narrow.

I'm dead set against a 1-in-36 chance of automatic failure.  That's a universe that doesn't work on a very fundamental level.

I've said something very similar in the past. Really though, it depends on what factors are being abstracted into the roll, and how exactly "failure" is being implemented.

And I'd say the reverse is also true. A universe in which you can stack bonuses in such a way that it's impossible to fail certain rolls (such as my mid-level Pathfinder game, where characters are routinely +20 ahead of the rest of the party within their chosen specialties) doesn't work on a fundamental level either.
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Daryk

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Re: Exploding 2d6
« Reply #6 on: 03 February 2017, 20:34:19 »
The auto-success universe is a bit different from the auto-fail one, I think.  It comes down to where you draw the line on requiring a roll at all.  Firing a weapon in combat usually merits a roll, and 1-in-36 odds of a weapon system failure in combat conditions would mean that weapon system would never be built in the first place (Ultra AC's, I'm looking at you first, with HVACs (yikes!) and RACs close behind).

skiltao

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Re: Exploding 2d6
« Reply #7 on: 03 February 2017, 21:33:05 »
I agree the universes are different.

Ignoring ultras and RACs, though, a 1-in-36 "autofail" rule isn't purely attributable to the weapon - sweat might drop into the pilot's eyes at the wrong moment, hands slip on the stick, bit of ground (under the shooter or the target) turns out to be softer than expected, the wind gusts wrong, some % chance on whether the attacker has rotated far enough fast enough vs. where exactly the target is in their movement at the time of firing.

I think the in-game failure rate on ultras and RACs is similar to the problem with ammo explosions - they have to be calibrated to happen with an entertaining frequency in real-life face-to-face playing time, rather than however often they would "really" happen in the fiction (also a disadvantage for computerized play).
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YingJanshi

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Re: Exploding 2d6
« Reply #8 on: 03 February 2017, 21:42:14 »
Huh...with a title about "exploding dice", I kinda thought this would be about Hellbie...my mistake...

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ialdabaoth

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Re: Exploding 2d6
« Reply #9 on: 06 October 2017, 06:36:15 »
Properly exploding 2D6 should be "add a die each time a die rolls '6'".

This gives you the same curve as standard 2D6 for target numbers under 7, and then 'stretches' the 7-12 probabilities out to 7-18, and gives a 'long tail' past 18 of ever-diminishing (but still theoretically achievable) odds.

The great thing about 2D6 [explode on '6'] is that you never get 'gaps' or 'plateaus' the way you can with a single exploding die (i.e., where the probability of TN7 is identical to TN6) - adding a +1 difficulty will *always* slightly reduce the probability of success.

I rather enjoyed a variant where ranges were extended to sane real-world values, by using exploding dice and giving every weapon a "range factor" equal to its Short range, with a +1 modifier per "range factor". So a Small Laser gets +1 per hex, while a Large Laser gets +1 per 5 hexes. Of course, you have to set a hard cut-off somewhere (at least with missiles and ballistics), or it starts getting a bit absurd.

Thunderbolt

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Re: Exploding 2d6
« Reply #10 on: 06 October 2017, 07:55:11 »
What about this...

for every 1 extra point of TN > 12, you have to roll one extra 1d6...

but always count the lowest two

et vice versa for every point of TN < 2, you get to roll an extra d6...

and count the highest two

on whichever 2d6 actually matter, 2 = miss, 12 = hit

Daryk

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Re: Exploding 2d6
« Reply #11 on: 06 October 2017, 13:34:09 »
Interesting ideas... what do the probability curves look like?

Thunderbolt

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Re: Exploding 2d6
« Reply #12 on: 10 October 2017, 12:11:34 »
I think it's similar to the earlier suggestions...

12 = 6 + 6
P(12) = 1/6 x 1/6 = 1/62

13 = 6 + 6 + 6
P(13) = 1/63

14 = 6 + 6 + 6 + 6
P(14) = 1/64

etc.
P(12+N) = 1/62+N

et vice versa.
P(2-N) = 1/62+N

Think that each additional point of TN above 12 / below 2 reduces the probability of a hit / miss by a factor of 1/6th.

Daryk

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Re: Exploding 2d6
« Reply #13 on: 10 October 2017, 20:09:24 »
Ah, I see... you need to roll an extra six on another die for each point.  Interesting, but I think that drops the probability too fast after 12.  That's a mighty steep curve!

DOC_Agren

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Re: Exploding 2d6
« Reply #14 on: 11 October 2017, 21:05:07 »
Properly exploding 2D6 should be "add a die each time a die rolls '6'".
I have to agree with this, twice in 2 different game systems I have watched exploding D6 bring about funny results

Shadowrun 2nd, the Street Mage with the Streetline Special, and a gun skill of 2, dropped a Troll Merc with 1 shot and like 16+ success followed by a GM going what can go wrong, and dropping the handful of body dice out where we all could watch and the # of 1 that popped up was amazing.

Full Thrust I personally engaged at long range a Kra'vak Superdread with a NSL Battleship and totally crippled it before it could could cripple myside.
"For the Angel of Death spread his wings on the blast, And breathed in the face of the foe as he passed:And the eyes of the sleepers waxed deadly and chill, And their hearts but once heaved, and for ever grew still!"

 

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