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# Experimenting with Anim Dynamics

I’ve been playing around with this a bit. I seem to get expected results with Linear movement and springs. I don’t seem to get any rotational/angular movement with the same non-animated leaf joints by default. There is a section in the Twitch stream where Charles mentioned there should be a local joint offset in the animDynamic settings, otherwise it wouldn’t do anything because it doesn’t know where to pivot from. I don’t quite follow that as it should have a pivot initially and the offset, should be an offset from the original joint pivot, both should logically work. Perhaps I don’t fully understand what he meant by that. In any case I tried several offsets and high/low values of angular limits with no visible results for angular movement.

There is a point where Charles mentioned in the twitch stream that he did some animation to get some of the cloth to move, (26:35). Is it expected that we should have animated the bones prior to using just angular movement? If I had a pad joint that is a child of the thigh bone it should receive motion from the parent without having to using a driven node and still use animDynamics to generate secondary motion. Is this not expected or do I need to use a bone driven node to force the motion down to the pad leaf joint?

Following up.

I think I’m getting a bit more familiar with the details. It seems using the offset makes it behave more like a pendulum system than a pivoting spring system. Knowing that’s how it behaves, its making more sense.

Yes, its not about the “where it pivots from”, but more a “where it pivots to”. As you said, it already has a pivot - itself!. But if you move an object that is anchored around its physical center of mass, it wont react with rotational movement.
If you move its center of mass, the physics law of inertia will force it to rotate accordingly. Thats what the settings mean. (At least I guess so by thinking the logics through.)

Also in the stream he mentions the nodes happen after the animation so it doesnt matter if you animated the joints themselves or not. But depending on what you wanna do with it, it might be good to have some level of control over it by pre-defining the movement with some handmade animation.

We recently implemented Anim Dynamics on our Characters. And turned out that accelerations are in local space. Acceleration from animation as an effect but acceleration from moving the pawn doesn’t. Anyone figured out how to get the pawn motion to affect the simulation?

Anybody know what the Angular Target Axis does in the Constraint? The tooltip says “Axis on body1 to match the Angular target direction”; and I have not found any other documentation.

“Yes, its not about the “where it pivots from”, but more a “where it pivots to”. As you said, it already has a pivot - itself!. But if you move an object that is anchored around its physical center of mass, it wont react with rotational movement.”

I guess that is to override the target point for angular movement dynamics. Tho im not completely sure.

Up !

We have the same issue as Birobinet : " And turned out that accelerations are in local space."

Yeah ive complained about that too. One possible workaround I could imagine is if you get the movement vector of your pawn and connect the inverse of that into the wind vector of the animDynamics node. Unfortunately it doesnt seem that that attribute is a connectable plug (or I just didnt figure out how to connect that yet).
Would be awesome if Epic could improve the node in that aspect, either that or have a checkbox that lets you have the sim run in world space or local space.

1- Local Joint Offset should be named Mass Offset (Box Offset)
2- Angular Limits should not be centered on the Mass but on the joint. It is very confusing