The Most Unusual D&D Random Number-Generating D10 We’ve Ever Seen

Matthew Dockrey has been watching a lot of Dimension 20, the fantastically imaginative Dungeons & Dragons show created and DM’d by Brennan Lee Mulligan and broadcast on Dropout. That entertainment got Dockrey thinking about the grandaddy of random number generators: the die. A well-made die is an incredibly elegant device, capable of producing true random numbers in a compact, inexpensive, and battery-free package. But there are many other RNG form factors available if those factors aren’t important and Dockey built the most unusual implementation that we’ve ever seen.

To understand how this works, you should first imagine something like the big spinner from Wheel of Fortune, but perfectly balanced. Now cut that down to 10 spaces and then shrink it to approximately the size of an appetizer plate. When the user spins the wheel, they have an equal 1:10 chance of landing on any specific space — at least in theory.

In reality, even a spinner with perfect balance and very good bearings won’t be truly random, as there is a direct correlation between the initial input force imparted by the user and the number of rotations. Someone trying to achieve a specific result could, with enough practice, probably improve their odds to be better than random. But we’ll ignore that and assume that players are spinning in good faith.

Here’s where it gets really interesting: the results of the spin show up on a seven-segment display, but this doesn’t contain any electronic components at all. Instead, this is a mechanical seven-segment display with each segment backed by a mechanism similar to that of a flip-dot display. Expose the pole of a segment to a magnetic field and it will flip one way. Expose the same pole to a magnetic field with reversed polarity and it will flip the other way. Each segment is bistable and will remain in its last position until set to a new one.

The physical build is very satisfying, as Dockery milled the parts from solid blocks of aluminum. A base and frame hold a bearing, as well as the seven-segment display. The spinner wheel attaches to the bearing so it can rotate freely. On each of the spinner’s 10 spaces, there is an arrangement of magnets, each oriented so its polarity either flips a segment “on” or “off.” The “0” space will only flip on the outer segments, the “1” space will only flip on two of them, and so on.

Dockery weighted the spinner so that it will naturally settle with a space’s magnets aligned with the display. But even if they don’t, the display will remain set until the next space’s magnets change the segments to something else. Not only is this fascinating to watch in action, but it is very pleasing to hear the segments flipping in rapid succession as the wheel spins.

This all makes us confident that Brennan Lee Mulligan would love to use Dockery’s D10 spinner in place of The Box of Doom for some special occasions.