This robot makes small jerky movements. I think the others are much more natural in appearance. Perhaps it is more of a hardware issue than software, as it does seem to have pretty good balance.
Truer than you know. The reason the Asimo's gait looks so smooth is that it's preprogrammed. It doesn't balance dynamically. It looks smooth for the same reason animation does.
That's not technically true. Asimo has preprogrammed paths, but not motor movements. Even in a semi controlled environment, a preprogrammed biped would fall.
The difference is between electric motors and pneumatics: today's pneumatics are just jerkier.
And static balancing doesn't mean that it is preprogrammed, just that at any point (unless it is running), all movement could stop and the robot would stay standing.
If humans stop moving, we collapse.
I guess the best reason to say Asimo is not more natural is that no animal in nature is statically stable. All animals with legs have actuators with the characteristics of pneumatics and springs (in humans, tendons are springs).
We can also turn to efficiency. The electric motors on Asimo will _never_ be practical. It takes too much energy for the bot to ever be sold as a product. No animal in nature has a 15 minute battery life :)
static balancing doesn't mean that it is preprogrammed
Really? That's what I was referring to when I said the gait was preprogrammed. I assumed that static balancing meant that the robot was only willing to traverse certain paths through the n-dimensional space of possible limb configurations, and that since these could be calculated in advance, they would be. But since I know you know about robotics, I'm willing to be convinced otherwise.
There are constant adjustments made by the dozens of motors in the legs and torso to keep balance, based upon sensors like accelerometers and gyroscopes. That's not preprogrammed.
My point about a reasonably controlled environment is that in the real world, even on a "flat" stage for a show, there are enough irregularities to make complete preprogramming hopeless.
I don't know enough control theory, but it could be stated that an open loop controller will be doomed to fail for a biped.
Higher level, there are sequences of commands that yield a step forward or to the side. That is almost certainly preprogrammed. When you own an asimo, the api they expose is actually really limited. For example, to lift the arm from the side to the air will only have a few states in between, and you choose which one you want. This is not low level control at all. They do this because they know Asimo is a marketing machine, not a real robot, and they don't want grad students making it fall over on youtube.
On second thought, a flamingo standing on one leg might actually be statically stable, and there might be other examples. But flamingos are weird, amirite?
http://www.youtube.com/watch?v=_CQ5AKaEi3U
http://www.youtube.com/watch?v=ZnTy_smY3sw