Small Object Contact Interaction

[jiaqixuac]

Hi, I'm working on a simulated surgical arm with tiny objects (~milimeters precision required).
I find it's rather tricky for physics simulation.


The torus has a radius of 2cm.
See figures before and after closing the gripper. It makes the torus inside the ground instead of grasping it.
Could you advise on how to enable accurate physics interaction, e.g., grasping for these small objects?

#1936

[xissburg]

Perhaps because the contact points are being merged due to the contact breaking threshold not being low enough?

Here you can see where they get merged if they're too close

bullet3/src/BulletCollision/NarrowPhaseCollision/btPersistentManifold.cpp

Line 192 in b1f7696

int btPersistentManifold::getCacheEntry(const btManifoldPoint& newPoint) const

and here is where it's calculated and passed to the constructor of btPersistentManifold

bullet3/src/BulletCollision/CollisionDispatch/btCollisionDispatcher.cpp

Line 74 in b1f7696

btScalar contactBreakingThreshold = (m_dispatcherFlags & btCollisionDispatcher::CD_USE_RELATIVE_CONTACT_BREAKING_THRESHOLD) ? btMin(body0->getCollisionShape()->getContactBreakingThreshold(gContactBreakingThreshold), body1->getCollisionShape()->getContactBreakingThreshold(gContactBreakingThreshold))

Perhaps you could try decreasing the value of gContactBreakingThreshold here

bullet3/src/BulletCollision/NarrowPhaseCollision/btPersistentManifold.cpp

Line 26 in afa4fb5

btScalar gContactBreakingThreshold = btScalar(0.02);

[jiaqixuac]

Perhaps because the contact points are being merged due to the contact breaking threshold not being low enough?

Here you can see where they get merged if they're too close

bullet3/src/BulletCollision/NarrowPhaseCollision/btPersistentManifold.cpp

Line 192 in b1f7696

int btPersistentManifold::getCacheEntry(const btManifoldPoint& newPoint) const

and here is where it's calculated and passed to the constructor of btPersistentManifold

bullet3/src/BulletCollision/CollisionDispatch/btCollisionDispatcher.cpp

Line 74 in b1f7696

btScalar contactBreakingThreshold = (m_dispatcherFlags & btCollisionDispatcher::CD_USE_RELATIVE_CONTACT_BREAKING_THRESHOLD) ? btMin(body0->getCollisionShape()->getContactBreakingThreshold(gContactBreakingThreshold), body1->getCollisionShape()->getContactBreakingThreshold(gContactBreakingThreshold))

Perhaps you could try decreasing the value of gContactBreakingThreshold here

bullet3/src/BulletCollision/NarrowPhaseCollision/btPersistentManifold.cpp

Line 26 in afa4fb5

btScalar gContactBreakingThreshold = btScalar(0.02);

Thank you for your suggestions.
However, it still fails maybe due to collision margin and other jittering effects.
Could it a better way to scale everything up?
I find that there is a long history of discussion for small objects.