27-10-2025, 03:51 PM
(This post was last modified: 27-10-2025, 03:54 PM by josemendez.)
(27-10-2025, 03:31 PM)Qriva0 Wrote: When there are different masses, the rod (that is expected actually) behaves like it was thinner or thicker in some places, but this causes natural propagation to break sagnificantly.
Oh, I see what you mean. While this doesn't have anything to do with stability (as in numerical stability), its a limitation of how dual descent solvers work indeed. Constraints involving particles with different masses bias the correction towards the particles with lower mass (which is physically accurate), so heavier particles receive a smaller percentage of the correction per iteration. However since the amount of iterations/substeps is finite this means lighter particles end up propagating less data to heavier particles, which makes convergence slower. Primal solvers have the same issue with stiffness ratios. Here's a good read on the subject: https://mmacklin.com/primaldual.pdf
Forcing specific mass ratios, by for instance clamping them is a typical (if unphysical) solution in games, this is what Unity joint's connectedMassScale is used for.