Animate digital creatures with this pliable modular doll (Wired UK)

ETH Zurich

This input puppet can be manipulated by hand in order to
generate movements in an on-screen animated 3D character.

A team from the Interactive
Geometry Lab at ETH Zurich
developed what they call “input
puppets” using 3D-printed modular blocks that can be connected
together to create any character shape. The modules have embedded
sensors at each joint to measure how it is bending and twisting,
which can be quickly mapped to virtual characters in order to
directly transfer that information.

This means that animators can physically manipulate an object in
order to change the way a digital model moves. So a four-legged
skeleton figure can be manipulated IRL in order to move an animated
elephant on screen, for example. This provides an alternative to
using the computer mouse or touchpad to drag virtual limbs into
poses for each frame. It’s also cheaper than vision-based systems
such as motion capture.

Tangible and Modular Input Device for Character ArticulationAlec Jacobson

“The key application is to animate characters for computer games
or movies. Since the device is “physically there”, you can hold it
in your hands and it is three-dimensional, it becomes much easier
to pose a character than manipulating its virtual representation on
the computer screen using keyboard and mouse. It is almost like
playing with a doll,” explains Professor Olga Sorkine-Hornung from
ETH Zurich’s Institute of Visual Computing.

It’s certainly not the first mechanical skeleton to map movement
to an on-screen character — this was something pioneered in the
making of
Jurassic Park
with a “Dinosaur Input Device”
. The
difference is that these new input puppets are reconfigurable and
measure angles with high precision.

The hardware comprises of multiple modular nodes, including
joints with embedded sensors, static splitters that allows for
branching in the skeletal tree and static extension segments to
increase separation between joints and splitters. The whole
skeletal tree connects to the host computer via the controller,
which transmits data and powers the other nodes. All of the nodes
are 3D-printed and the circuit schematics have been published by
the researchers.

Sorkine-Hornung told that the biggest challenge was
allowing for the maximum amount of degrees of freedom while keeping
the device small — ideally something that could fit on a desktop.
“Standard sensors and other electronics available for prototyping
are usually pretty large, so each piece of the device would have
been at least twice as big.”

The team eventually decided to use a small sensor type called a
Hall sensor while using a joint design that decoupled the bending
motion from the twisting motion. “This enables nearly maximum
motion range and results in pieces only about 1.5-cm thick,” she

Each joint has a dedicated microcontroller to acquire data
relating to the angle the joint has been manipulated into and this
is shared with the central controller. Each component has a small
amount of memory to store information such as unique ID, node type
and colour.

To calibrate the model to the animation, the skeleton has to be
placed into a specific “rest pose”. The joints of the model need to
correspond to the joints on the animation, with the lengths between
neighbouring nodes having to match up on-screen.

For particularly complex animations, different parts of the
creature can be modelled separately. So a monster’s arm movements
might need careful manipulation, while the rest of its body remains

“The modularity of our device allows users to perfect and refine
their working device to match the complexity of the desired
articulation,” explain the authors.

You can read the research paper here.

Beyond video game and movie animation, the team is considering
other applications “such as special controllers for video games,
and devices for studying the human perception of 3D posing and
motion,” says Sorkine-Hornung.

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