"Are these going to be of any use?" Topic

Adverts for these dice keep arriving in my inbox.

link

Mmmmmm I thought, unusual. But when I looked closer I got the feeling that they would be very unlikely to give you a result other than '7', or whatever number is on the opposite side of the '7'.

Any thoughts?

I am curious to see how well they roll. They are certainly of use…especially in games where unit quality is based on a die type…like Dirtside or Pride of Lions. This would open up a new "step" in quality. Maybe hardened militia where the normal militia would be a d6.

Without doing the math, isn't the point of a die as a reliable randomizer that each surface have the same area? (Assuming surface area equates to friction which equates to cessation of tumbling and movement.)

I know we all think the angle where the faces meet (vertices?) is significant, but it's accepted that a D6 randomizes reliably and that cube shape has 90 degree angles, which surely are the least likely to tumble as the distribution of weight affecting balance appears even at that angle. All polyhedral die shapes have shallower angles than that.

So perhaps the only factor truly is for the surface area of the faces to equal each other.

Looking at this design it seems by varying the thickness one could achieve square faces with the same surface area as the pentagonal faces.

So even though it looks odd, it should randomize without bias.

five quid!!! just use a d10 and a d4 if you really need a 1-7 roll.

bridget midget the return: … use a d10 and a d4 if you really need a 1-7 roll.

? (D10+D4)/2 rounded up? Doesn't that give a bell curve not a flat curve?

Answer: Obviously yes, the question was rhetorical:

	1	2	3	4			
1	1	2	2	3			
2	2	2	3	3			
3	2	3	3	4			
4	3	3	4	4			
5	3	4	4	5			
6	4	4	5	5			
7	4	5	5	6			
8	5	5	6	6			
9	5	6	6	7			
10	6	6	7	7			
Distribution:						
1	2	3	4	5	6	7
2.5%	12.5%	20%	20%	20%	17.5%	7.5%

Oh that's right, I forgot about the rounding shifting the lowest value. So it's not just a bell curve, it's a skewed bell curve. (Note if you round down instead of up, you get the mirror of this distribution, with the highest value appearing less.)

If you want a distribution simulating a single die numbered 1-7 (i.e. a flat curve), use a D8, and reroll the 8s, repeating if necessary until the value is in the range 1-7.

I have a pair of these, but I've never used them in a game. I think I may get them out and roll around a few hundred times tomorrow to find out if they are random.

A heptagonal prism would be more reliable.

A D14 is available. These could be numbered 1 to 7 twice.

I realize I'm jumping into a cold topic here, but his is something I find intriguing, so in hopes others may still be interested:

@CerulLucifus: It turns out equal surface area does not result in equal probability for each side landing up in dice where different sides are different shapes. I've experimented with this as part of an ongoing process of developing unique polyhedral dice; I'm currently working on some dice that include both pentagonal and hexagonal sides, and unfortunately just equalizing the surfaces won't result in fair dice. It turns out the pentagons are significantly more likely to appear than the hexagons relative to their frequency. I have some theories as to why this is so, but I suspect the math behind it is insanely complex.
So, the 7-sided die pictured may well be a fair die, but only if the relative areas of the different shaped sides have been optimized to account for geometric differences. Just how practically possible this is I'm not sure as far as creating a true perfect fair die, but I'm sure one can be made that is close enough it should be acceptable to anyone but a nuclear physicist.
…
If anyone actually wants a 14-sider numbered 1-7 twice (and precisely equal on all sides), PM me and I can work up one for you on Shapeways.

I wouldn't rely on them.

You can have a 1-7 effect with D6. In my own rules ("Argad") when a 7 is required it means that you must roll two 6. It makes a difference between what happens quite often (1-2-3-4-5-6) and what is very difficult but not impossible (ex: a smoothbore musket at long range).

1-7 using only d6 requires far more than two unless rerolls are ok? Dont remember the best way but I spent too much time once figuring out ways to get fair 1-n from d6 and n=7 was no fun iirc.

EDIT: Or is n=7 not even possible?

Wrote a very quick script to get how many d6 are needed to get different other dn without rerolls (but probably not 100 % correct):

d2 from 1d6
d3 from 1d6
d4 from 2d6
d6 from 1d6
d8 from 3d6
d9 from 2d6
d12 from 2d6
d16 from 4d6
d18 from 2d6
d24 from 3d6
d27 from 3d6
d32 from 5d6
d36 from 2d6

1-7 using only d6 requires far more than two unless rerolls are ok? Dont remember the best way but I spent too much time once figuring out ways to get fair 1-n from d6 and n=7 was no fun iirc.