I was going to write a short post about using After Effects expressions to capture the “feel” of machines. But I got so distracted by this simple example I put together:
click for
/pixelblog/content/2007/machine/pulleys.swf
The behavior comes about naturally; the big wheel has its rotation controlled by the little wheel’s rotation divided in half. And the little wheel, in turn, is controlled by the y-position of the blue slab.
What struck me was the accidental (but obvious, now) trick of exposing an offscreen action with onscreen elements. We “know” that the wheels are associated with the blue slab’s motion. So when they spin for a while, we know it’s rising and, momentarily, falling.
So what happens if you break that assumption? I guess it is “surprising” or even, just maybe, funny…
click for
/pixelblog/content/2007/machine/pulleys_aha.swf
thisComp.layer("Cyan Solid 1").transform.position.valueAtTime(time+.2)[1] * 4
You can link together a handful of elements’ motions and effects to get arbitrarily nifty and complicated machines! Here’s a sort of microscope, where expressions are used to control a simulated rack focus effect.
click for
http://www.youtube.com/v/_53MuimmrAs&rel=1&loop=1