Aw, I forgot to click post reply.
Oh you are right, yes I did what you described and touched both values. In addition I noticed there is way bigger change when value is like 0.01 than 10 or 100 and I tried to operate more around 0.1-10. What was counterintuitive for me right now is that compliance 0 and different masses can change rigidity of rod itself even when there are no collisions, I thought that if I want very rigid rod I need to set it to 0 and that is max I can get, meanwhile ratio of rotational mass and mass changes rigidity completely.
I have one question, but it's more about next version of obi (with compliance factors per particle), what is difference then, between rotational mass ratio and compliance for bending? I understand there is difference I can kind of feel it, but overall both control similar thing. Does it mean that with new system I can set big rotational mass to make rod very rigid, but then set compliance to big value and the result would be rigid rod, but with capability to bend sagnificantly during collision?
Does it actually mean I can create similar behaviour even right now by increasing rotational mass of the whole rod?
Because that is my goal, responsive and "rigid rod" when it comes to movement, but at the same time bendable when colliding with other (static) objects. (so far rigidity meant it behaves like rod made of iron)
(21-10-2025, 10:14 AM)josemendez Wrote: I believe you're changing both mass and rotational mass, not rotational mass alone (as in inertia tensor magnitude). Uniformly changing both doesn't have any effect on rod rigidity, as linear to angular momentum ratio is kept fixed.
Changing rotational mass *only* does have a very large impact on rod behavior, as it should. Just tested in the "SpringRod" sample scene by selecting all control points and increasing/decreasing their rotational mass while leaving mass intact. This is equivalent to scaling the inertia tensor of a rigidbody in Unity.
Keep in mind that the inertia tensor is to angular moment what mass is to linear moment: it modulates the effect of torques (angular "forces") on velocity:
Linear: Force = Mass * linear acceleration.
Angular: Torque = Inertia tensor * angular acceleration. (in literature, tau = I * alpha)
If you change both mass and inertia tensor together (which is what MassScale does), there will be no qualitative effect on body behavior. However if you change their ratio, behavior will change since the object is now easier/harder to rotate than it is to translate. Applied to a rod, this means it's easier/harder to bend than it is to stretch.
Hope this makes sense. Let me know if I can be of further help!
Oh you are right, yes I did what you described and touched both values. In addition I noticed there is way bigger change when value is like 0.01 than 10 or 100 and I tried to operate more around 0.1-10. What was counterintuitive for me right now is that compliance 0 and different masses can change rigidity of rod itself even when there are no collisions, I thought that if I want very rigid rod I need to set it to 0 and that is max I can get, meanwhile ratio of rotational mass and mass changes rigidity completely.
I have one question, but it's more about next version of obi (with compliance factors per particle), what is difference then, between rotational mass ratio and compliance for bending? I understand there is difference I can kind of feel it, but overall both control similar thing. Does it mean that with new system I can set big rotational mass to make rod very rigid, but then set compliance to big value and the result would be rigid rod, but with capability to bend sagnificantly during collision?
Does it actually mean I can create similar behaviour even right now by increasing rotational mass of the whole rod?
Because that is my goal, responsive and "rigid rod" when it comes to movement, but at the same time bendable when colliding with other (static) objects. (so far rigidity meant it behaves like rod made of iron)