SIGGRAPH 2010: Optimal Feedback Control for Character Animation Using an Abstract Model

[daEmoNicky]

Are those ground forces on feet proportional to pressure on feet?

[yutingye]

@daEmoNicky The pressure on each foot can be computed by summing up all the forces and divide the aggregated force by the foot area. Currently, forces are applied at the four corners of the cube like feet.

[daEmoNicky]

What do these pink vectors represent? (I assume it is some force.) Thanks. :)

[yutingye]

@daEmoNicky

Yes, The pink vectors represent the ground reaction forces applied to the character. And the pink dots are the points of application. The red vectors are external perturbation forces, i.e. pushes.

[daEmoNicky]

@yutingye And the force applied on the feet propagates to the rest of the body so it keeps the balance?

[yutingye]

@daEmoNicky The optimal ground reaction forces are computed to prevent the character from falling while performing the desired actions. The effect of the forces on each body part is not considered explicitly due to the complexity of the dynamic system. Instead, the entire character is simplified to a mass point so that planning of forces for the future is possible.

[daEmoNicky]

@yutingye And that character is trying to keep balance with hands, bending torso, head and legs is somehow derived from that mass point?

[yutingye]

@daEmoNicky The mass point provides the desired linear and angular momenta of the full body, which are computed from the ground forces through numerical integration. The character then tries to move all the body parts to satisfy these momenta. In addition, there is a reference motion that the character is trying to follow (e.g. walking, squatting etc).

[LovetoryLoveMachine]

@yutingye How? I imagine it might be done this way: The centre mass point obtains one momentum from feet, then momenta for each body part are computed. Each body part is represented by mass point. I imagine it is this way "angular momentum of body part (represented by mass point) = distance of that body part to centre * linear momentum of centre" and that angular momentum should be made in opposite direction, which woul make body part ""want to" balance(go against movement causing imbalance).

[yutingye]

@LovetoryLoveMachine The momenta of the full body is the sum of momenta of every body part, which in turn is a function of all the degrees of freedom of the body (global translation, rotation, and joint angles). Given desired momenta and the current configuration of the character, velocities of the configuration can be computed and integrated to get the next configuration.

[LightningBeast]

when he walk up the stairs he looks like a fat guy,struggling to get there ,though he's slim lol

[Marius426]

Leave this poor guy alone... :( What you call perturbation is just bullying... ^^

Interesting stuff actually.

[yutingye]

@Marius426

Glad someone pointed this out. But the perturbations are actually quite mild and the guy simply exaggerates the reaction to gain sympathy :)

[ninthjake]

So the character is still driven by an active animation with balance-based constraints or is the character really balancing on it's own similar to Euphoria?

[yutingye]

@ninthjake

The character is balancing "on its own", and it will fail in challenging situations.

[Sobianful]

Very similar to euphoria engine.