Yoshimoto Cube

tags: [fidget] [geometry] [flexure] [flex] [bistable-mechanism] [compliant-mechanism] [3d-printing]

Also known as:

interesting links/references:

It’s got interesting geometry: it’s not the same cube repeated 8 times, the middle 4 cubes are actually different.

apparently, the geometry also kind of works with just 4 cubes:

3d printing it

there’s plenty of models of this cube to print, with print-in-place hinges.

TPU/flexible designs are interesting to me. usually, they suffer from the issue that the hinges have a ‘resting position’ and so it is less satisfying to fidget with.

There are some designs with magnets

bistable hinges

I’m most interest in how to make one of these with bistable hinges. Because that would be really cool, I think.

challenges/design goals:

I have made a few prototypes so far:

spring/elastic/rubber band
An elastic spring on the inside works pretty well. This hinge is most tensioned at the midpoint between the two resting positions, which means it must have a high resting tension in order to hold the hinge in the reverse of it’s rest position reliably (where the hinge has rotated 180 degrees from the orientation in which it was printed).

I have tried, in a different design, to change the length of the in-hinge cut so that the elastic band has more leverage when the hinge is 180 out of resting position. But then you run into problems of the total length of the elastic: when all the hinges in the cube are in their reverse position, the total length of the elastic is thusly much smaller, and so it isn’t stretched as much and doesn’t exert as much force to hold the cube in shape.

This works pretty well, actually. Magnets are relatively expensive, though, and also it’s much less easy to tune the exact tension in each hinge. Also, it has a tendency to snap into place, and that snap can be noisy…

gear hinges

could be cool, but it’s hard to print the gears small enough. Also, gears are particularly sensitive to print orientation, or else they don’t turn out very well.