This interview was with Jay Shuster, a designer behind Pixar films including Cars (2006) and Wall.E (2008), having a background in mechanical engineering, he gave this interesting interview discussing streamlining it with overall character design.
John [Lasseter] was really, really into maintaining the authenticity, the honesty of the materials in the design of those characters.
He’s right there at the edge. We maintained a size but kept him cute — he couldn’t just be a gigantic earth-moving machine. We wanted to work with a certain-size package to keep his character. We did have to cheat a bit, allowing for his head, the arms, the treads to fold into his body. Everything does kind of collide inside, but we worked really hard to get to a point where the animators could run with it and make him look like he really works.
Explaining Designs in detail (Cars)
“This is a concave area,” “you need to smooth out the transition between the hood and the fender” and so on — stuff that was inborn in me growing up in Detroit, kind of knowing what a car looks like and how it was manufactured. That was a very gratifying part of actually working here, first on Cars and then on WALL•E, was finding that knowledge again and being able to use it to make these characters as convincingly real — and as honest — as possible.