Rigging Your 3D Models In The Real-World

3D Real-World Rig

Computer animation is a task both delicate and tedious, requiring the manipulation of a computer model into a series of poses over time saved as keyframes, further refined by adjusting how the computer interpolates between each frame. You need a rig (a kind of digital skeleton) to accurately control that model, and researcher [Alec Jacobson] and his team have developed a hands-on alternative to pushing pixels around.

3D Rig with Control Curves

Control curves (the blue circles) allow for easier character manipulation.

The skeletal systems of computer animated characters consists of kinematic chains—joints that sprout from a root node out to the smallest extremity. Manipulating those joints usually requires the addition of easy-to-select control curves, which simplify the way joints rotate down the chain. Control curves do some behind-the-curtain math that allows the animator to move a character by grabbing a natural end-node, such as a hand or a foot. Lifting a character’s foot to place it on chair requires manipulating one control curve: grab foot control, move foot. Without these curves, an animator’s work is usually tripled: she has to first rotate the joint where the leg meets the hip, sticking the leg straight out, then rotate the knee back down, then rotate the ankle. A nightmare.

[Alec] and his team’s unique alternative is a system of interchangeable, 3D-printed mechanical pieces used to drive an on-screen character. The effect is that of digital puppetry, but with an eye toward precision. Their device consists of a central controller, joints, splitters, extensions, and endcaps. Joints connected to the controller appear in the 3D environment in real-time as they are assembled, and differences between the real-world rig and the model’s proportions can be adjusted in the software or through plastic extension pieces.

The plastic joints spin in all 3 directions (X,Y,Z), and record measurements via embedded Hall sensors and permanent magnets. Check out the accompanying article here (PDF) for specifics on the articulation device, then hang around after the break for a demonstration video.

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Interactive dice game pits man against machine

dice_game

While most dice games are based on luck and chance more than anything else, [Mike] decided he wanted to create a dice game that took a little more skill to play. He built a replica of a game found in Ian Stewart’s “The Cow Maze”, a book of mathematical stories and puzzles.

The theory behind the game is as follows:

A number is randomly drawn and is considered the “heap”. Players take turns reducing the heap, using the die to represent the number they would like to remove. The only restrictions placed on moves are that you cannot re-use the same number chosen by your opponent in the preceding move, nor can you use the number on the die face opposite that number. The winner of the game is the individual reducing the heap to exactly zero, though you can also lose the game automatically if you reduce the heap to a negative number.

The game operates using a magnet-loaded wooden die and hall sensors built into the playing surface. The sensors relay the value of the die’s face to the ATmega chip he used to run the game. His code provides the logic for your computer opponent as well as for keeping score.

The whole project is wrapped up in a nice-looking wooden box that gives it a bit of old time-y charm, micro controller and LCD aside.

Be sure to check out the video below to see a few rounds of the game being played, and swing by his site for more details.

[via SparkFun]

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