11-09-2020, 12:28 PM
(This post was last modified: 11-09-2020, 12:34 PM by josemendez.)
Hi,
Even if spheres had a large contact patch against other objects, the fact that they are in contact during a very small amount of time when hit/bouncing (usually a single timestep) would negate any benefits of this, since you'd still have to resolve the contact in a single timestep. Contact surface area would not give you much additional information to aid in accurate angular velocity treatment, and you already have contact penetration depth available (btw, with penetration depth, you could even calculate contact area analytically in the case of sphere/plane contact if you wanted to).
The thing you want to simulate here is the effect of angular velocity on contact separation velocities, and to the best of my knowledge this can be done quite accurately even with a single contact point.
This behavior you refer to:
Is what angular friction (aka rolling friction) is designed to avoid. The idea behind this is that surfaces aren't perfectly smooth, so a rolling ball on the ground would eventually come to a stop due to micro-imperfections in the surface. In case of a soccer pitch (grass), these micro-imperfections are actually quite "macro", so the effect is more pronounced. It's usually implemented as a torque that counters angular velocity, by an amount dependant on the material friction and relative velocity of the involved bodies at their contact point. If you look for research articles on granular materials (sand, gravel), you can find info about that as they usually implement it.
Note that Obi does not model any of this either for the softbody case. More specifically, we do have rolling friction but only for granulars, which do not have restitution (bouncing).
All of it is very specific to the soccer use case. So still, rigidbody simulation will get you closer to your goal. Sure, there's some simplifications done by PhysX that result in lacking simulation, but imho re-adding them in some way is your best bet.
Even if spheres had a large contact patch against other objects, the fact that they are in contact during a very small amount of time when hit/bouncing (usually a single timestep) would negate any benefits of this, since you'd still have to resolve the contact in a single timestep. Contact surface area would not give you much additional information to aid in accurate angular velocity treatment, and you already have contact penetration depth available (btw, with penetration depth, you could even calculate contact area analytically in the case of sphere/plane contact if you wanted to).
The thing you want to simulate here is the effect of angular velocity on contact separation velocities, and to the best of my knowledge this can be done quite accurately even with a single contact point.
This behavior you refer to:
Quote:when the ball is rolling along the ground, it does not come to rest properly, it will just keep rolling indefinitely in some cases
Is what angular friction (aka rolling friction) is designed to avoid. The idea behind this is that surfaces aren't perfectly smooth, so a rolling ball on the ground would eventually come to a stop due to micro-imperfections in the surface. In case of a soccer pitch (grass), these micro-imperfections are actually quite "macro", so the effect is more pronounced. It's usually implemented as a torque that counters angular velocity, by an amount dependant on the material friction and relative velocity of the involved bodies at their contact point. If you look for research articles on granular materials (sand, gravel), you can find info about that as they usually implement it.
Note that Obi does not model any of this either for the softbody case. More specifically, we do have rolling friction but only for granulars, which do not have restitution (bouncing).
All of it is very specific to the soccer use case. So still, rigidbody simulation will get you closer to your goal. Sure, there's some simplifications done by PhysX that result in lacking simulation, but imho re-adding them in some way is your best bet.