Roll/keep probabilities?

[Jay Turner]

I'm toying with an idea for a game that uses a roll/keep system for piloting vehicles, and I'm trying to think of a way to use it for other things, too. Currently you roll dice equal to your vehicle's stat (say, Handling) and keep dice equal to your character's stat (say, Piloting). Those dice are then compared to an opposing roll, and whoever rolls highest wins.

I suck at probabilities, though, and I was wondering if anyone's done an analysis of roll/keep probabilities? Which affects the success of the roll more, the number rolled, or the number kept? Is there a chart or formula somewhere that I can use?

Thanks!

[Mike Holmes]

Are the number kept added, or compared in another manner?

Mike

[Jay Turner]

I was originally using a TN/success thing, but now I'm looking at an opposed roll mechanic similar to Ron's in Sorcerer.

For example:

Two pilots are dogfighting. Abe has Piloting 3 and is flying a plane with Handling 5, while Ben has Piloting 4 and is flying a plane with Handling 4.

Abe has Ben on his six, and he wants to maneuver and try to lose Ben. To do this, Abe must roll better on a Piloting/Handling check than Ben does.

Abe rolls 5 dice and keeps 3: (9 6 6) 5 3

Ben rolls 4 dice and keeps 4: (9 7 4 2)

Ben's roll is better, because the 9s cancel and Ben's 7 is higher than Abe's 6. Ben's degree of success is 1, because he only had 1 die higher than Abe's 6. Abe jukes and jives, but Ben is right on top of him all the way.

That's what I'm looking at right now.

[Mike Holmes]

OK, so you choose the highest in most cases (assumes that the player wants to win).

I can tell you right off that the player with the most dice is still the most likely to win. The high die in this system isn't affected by the number kept. The only thing the kept dice do is limit total number of successes (assuming that this is important).

Sounds pretty interesting.

Note if you kept the X lowest dice that would make a difference in chance to win.

Mike

[Jay Turner]

Interesting to know that. That means that in this case, the plane/vehicle is really what determines chance of success, with the character's skill determining the degree of success. Does that sound right?

Hrm. I'll have to think about what that means and if it fits my design goals. I'll also look into keep lowest dice, as well.

[Matt Wilson]

Hey Jay:

You might consider reversing the idea, so that the vehicle limits how many you can keep. With a Zero you can keep all your dice, but with a grumman goose you can only keep two.

That means skills are still really important, but better equipment will help you break ties when the opponents are equally matched.

[Jay Turner]

Hi Matt,

That's actually the way I'm headed now. I want Skill to be very important to whether you succeed or not, but Equipment to decide how well you do.

It also means that if you've taken enough damage to reduce the plane's Handling to 1, a high-skilled pilot would be more likely to successfully land than a rookie.

I think that looks good. :)