Figurines that just won't stay standing are the bane of a collector's existence, but spare a thought for hobbyists who design and 3D print their own models, only to find they keep toppling over. Now a team at Disney Research has developed a method for crafting 3D printable objects with metal balls embedded inside, which allows the average user to design models that can pull off some quirky balancing acts.

Movable masses are the name of the game, in the form of metal balls encased in cavities inside the object. These spaces, which the team call capsules, are modeled at the software stage of the process, to allow the ball to roll around and change the object's center of gravity, depending on its position.

Users enter a set of guidelines for how they want a particular 3D model to balance, including how the object needs to stand up, its floating in water, the hanging position when suspended on a string, or a combination of all of these. With those targets set, the system will figure out how many capsules that will require, along with their size and where they need to go inside the object.

Armed with some readily-available ball bearings, the user will need to pause the printing process to slip them into the cavities. The finished object should then stand, float or hang exactly as the designer intended, as demonstrated by a few examples the Disney team mocked up.

A Breakdancing Teddy is able to stand stable in six different positions with some help from two capsules, and a toy Dolphin shows a combination of two objectives: when placed in water, it floats with its nose facing upwards, but when suspended from a string by its fin, it will hang with its nose pointing towards the floor.

The Muscle Gnome, meanwhile, is articulated at the hip, and is designed so it will only stand upright when leaning to the left. Although it looks symmetrical, when angled to the right it will wobble over, thanks to the ball bearing in the log it's carrying.

With the ball and cavity concealed inside, the gnome is designed as kind of an optical illusion: from the outside, there doesn't seem to be any reason it won't stand up equally well at both angles.

And that's the point of this system, to help 3D printers design models with surprising balancing properties. The team says that the next step is to investigate using sand or fluids to balance the objects, instead of the metal balls.

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