I've been pretty much obsessed with robots for as long as I can remember. As a kid I used to draw designs for more utilitarian bots, mostly treaded. But now I'm thinking androids. I've been working on a design inspired by ball jointed dolls. You may have seen my sketch (or not because it's a scrap).

I've improved a lot on that drawing. My goal is to create something that moves as naturally and humanly as possible. To that end I've been examining photos of real people moving the way people do, and I have a few observations to make, which may benifit other dolls and poseable figures:

• Almost all dolls, figures and robots are unable to lift their shoulders. If humans could not do this, we would not be able to reach over our head. Making a fixed shoulder that is flexible enough to do this produces unnatural positions. My solution is to make a large ball joint for the shoulder with the arm set into a smaller joint inside that. Take a look at Asimo to get the idea if you can't picture it. Rotation of the larger ball moves the shoulder, and the smaller moves the arm.


• Most of us are used to thinking of the spine as a long flexible chord. While this is partly true, I have noticed that almost all of the bending in the spine occurs in a very small range just under the rib cage. Most of the subtle curve there is seen mainly in the soft tissues of the abdomen. A soft rubber cover over this space will create the same effect.


• The opposite is true of the neck. Most figures have a rigid neck with a single joint at the base of the skull, or even a neck that's integrated into to the head (as on many action figures). I won't make it too complicated, but I think two joints will suffice, one at the base of the skull and the other at the base of the neck itself. A flexible cover will create the natural-looking curve as with the abdomen.

Since I plan to actually build this figure (I'm not sure whether to call it a doll, but that's essentially what it will be), I do have to consider materials. I want it to look like a real industrial design, so I will be using appropirate materials and avoiding unnecessary fiddly bits that most robots have just to make them look robotic. And any good robot is easy to produce with durable and affordable materials. It turns out my first thought is also looking like the best option: PVC. Polyvinyl Chloride is a very durable plastic that also happens to be heat formable and, most importantly, really cheap. And it's easy to find in the form of pipes, which are already close to the shape I need.

The only other thing to worry about is the ball joints. I'm not sure whether I can make a ball out of PVC, but I will definitely try. If not, I'll have to find some alternative. If ball valves are cheap enough, I may just get some of those and break them open. They already have a convenient hole for stringing.

I'm going to start with a 60cm prototype, but I think in the future I might want to try a life size version. It may even be possible to put some simple actuators inside the shell, such as air muscles, which are easy to make.