Julio Jerez wrote:This demonstrates that we both are wrong in some, I am wrong because I expected the single foot to be more stable. and you were wrong when you say that keeping balance is so hard that losing a single contact for one frame is enough to topple the model down.
No, that's not what i mean when i talk about balance. My point is 'efficient' balance. I had balancing ragdoll on one foot, holding the second one up in the air, on a moving and rotating platform - and that was before you made the stiffer joints.
So what i mean with efficient balance is best described with this test setup:
Ragdoll stands straight, keeping both feet in place, making a step is not allowed.
Then make the ragdoll swing left and right in a periodic cycle.
And you set the target as placing the com of the ragdoll almost above the edge of the support area on both sides.
Try to make the ragdoll swing as fast as possible. And also do it yourself - depending on how wide the feet are apart, one swing should take a second or so.
I think that's the ultimate test. It requires to plan the full motion ahead, and how the system changes.
In fact, the more you come towards the edge, the less torque you can apply to break before tipping over. That means you need to start breaking in time, and if you miss the moment, you will tip over and only a step can prevent this.
The equations become a system of position dependent acceleration, where position means ankle nagle, and acceleration means ankle torque. The equation is hard, but closed form analytical. It's possible to calculate much time a swing will take, and from that you can determinate how 'efficient' your robot is able to act. That's what i mean.
This also implies there often is no state machine necessary, because you can predict the future and current possibility of action just from the current state of the system itself. It tells you where and when to place the next step etc, all without a need for a state machine that keeps track of itself using a form of memory.
And this is where my doubts come from - i doubt your solver is that smart to know this. But without it, no realistic motion, or at least no most efficient motion is possible, because humans act constantly in this 'most risky, but efficent' mode. Otherwise we would move like that Sony robot. I'm 100% sure Boston Dynamics uses exact that equation, and it is this one thing that makes them the only ones who get it right.
You will soon see yourself!
Julio Jerez wrote:I know is a big claim and as we make progress, you are right new finding may me change my hypothesis.
Yep, you will need to extend it. Let's bet a beer. We'll drink it when we meet in person, you know, while looking way doooown...