Brad Bird's Iron Giant was a 3D character built to feel hand-drawn
Making the Iron Giant Live
The Iron Giant's Giant was always meant to be a 3D character living seamlessly in a 2D world. Brad Bird's team built tools like Gartoons to give his lines a wobbly, hand-drawn irregularity, printed 3D frames onto peg-hole paper so 2D animators could match Hogarth's touch, and modulated frame rates so slow movements ran on twos. The result: a metal giant who could make a room cry.
The computer wants to animate everything on ones, which is 24 drawings a second. Whereas 2D animation mixes it up ... Slow movement works fine on twos and in many cases looks a little more stable, if it is really slow.