separate spinning friction (torsional friction around contact normal) from

rolling friction (orthogonal to contact normal)

data/r2d2.urdf

@@ -388,6 +388,7 @@
     <child link="head"/>
     <axis xyz="0 0 1"/>
     <origin xyz="0 0 0.3"/>
+<limit effort="1000.0" lower="-0.38" upper="0" velocity="0.5"/>
   </joint>
 
   <link name="box">

examples/Importers/ImportURDFDemo/URDF2Bullet.cpp

@@ -410,6 +410,10 @@ void ConvertURDF2BulletInternal(
 				{
 					col->setRollingFriction(contactInfo.m_rollingFriction);
 				}
+                if ((contactInfo.m_flags & URDF_CONTACT_HAS_SPINNING_FRICTION)!=0)
+                {
+                    col->setSpinningFriction(contactInfo.m_spinningFriction);
+                }
 				if ((contactInfo.m_flags & URDF_CONTACT_HAS_STIFFNESS_DAMPING)!=0)
 				{
 				    col->setContactStiffnessAndDamping(contactInfo.m_contactStiffness,contactInfo.m_contactDamping);

examples/Importers/ImportURDFDemo/URDFJointTypes.h

@@ -16,17 +16,20 @@ enum UrdfJointTypes
 enum URDF_LinkContactFlags
 {
 	URDF_CONTACT_HAS_LATERAL_FRICTION=1,
-	URDF_CONTACT_HAS_ROLLING_FRICTION=2,
     URDF_CONTACT_HAS_INERTIA_SCALING=2,
     URDF_CONTACT_HAS_CONTACT_CFM=4,
 	URDF_CONTACT_HAS_CONTACT_ERP=8,
 	URDF_CONTACT_HAS_STIFFNESS_DAMPING=16,
+    URDF_CONTACT_HAS_ROLLING_FRICTION=32,
+    URDF_CONTACT_HAS_SPINNING_FRICTION=64,
+
 };
 
 struct URDFLinkContactInfo
 {
 	btScalar m_lateralFriction;
 	btScalar m_rollingFriction;
+    btScalar m_spinningFriction;
     btScalar m_inertiaScaling;
 	btScalar m_contactCfm;
 	btScalar m_contactErp;
@@ -38,6 +41,7 @@ struct URDFLinkContactInfo
 	URDFLinkContactInfo()
 		:m_lateralFriction(0.5),
 		m_rollingFriction(0),
+        m_spinningFriction(0),
         m_inertiaScaling(1),
 		m_contactCfm(0),
 		m_contactErp(0),

examples/Importers/ImportURDFDemo/UrdfParser.cpp

@@ -672,7 +672,28 @@ bool UrdfParser::parseLink(UrdfModel& model, UrdfLink& link, TiXmlElement *confi
                   }
               }
           }
-
+          {
+              TiXmlElement *spinning_xml = ci->FirstChildElement("spinning_friction");
+              if (spinning_xml)
+              {
+                  if (m_parseSDF)
+                  {
+                      link.m_contactInfo.m_spinningFriction = urdfLexicalCast<double>(spinning_xml->GetText());
+                      link.m_contactInfo.m_flags |= URDF_CONTACT_HAS_SPINNING_FRICTION;
+                  } else
+                  {
+                      if (!spinning_xml->Attribute("value"))
+                      {
+                          logger->reportError("Link/contact: spinning friction element must have value attribute");
+                          return false;
+                      }
+                      
+                      link.m_contactInfo.m_spinningFriction = urdfLexicalCast<double>(spinning_xml->Attribute("value"));
+                      link.m_contactInfo.m_flags |= URDF_CONTACT_HAS_SPINNING_FRICTION;
+                      
+                  }
+              }
+          }
            {
            
               TiXmlElement *stiffness_xml = ci->FirstChildElement("stiffness");

src/BulletCollision/CollisionDispatch/btCollisionObject.cpp

@@ -33,6 +33,7 @@ btCollisionObject::btCollisionObject()
 		m_friction(btScalar(0.5)),
 		m_restitution(btScalar(0.)),
 		m_rollingFriction(0.0f),
+        m_spinningFriction(0.f),
 		m_contactDamping(.1),
 		m_contactStiffness(1e4),
 		m_internalType(CO_COLLISION_OBJECT),

src/BulletCollision/CollisionDispatch/btCollisionObject.h

@@ -85,7 +85,8 @@ protected:
 
 	btScalar		m_friction;
 	btScalar		m_restitution;
-	btScalar		m_rollingFriction;
+	btScalar		m_rollingFriction;//torsional friction orthogonal to contact normal (useful to stop spheres rolling forever)
+    btScalar        m_spinningFriction; // torsional friction around the contact normal (useful for grasping)
 	btScalar		m_contactDamping;
 	btScalar		m_contactStiffness;
 	
@@ -323,7 +324,15 @@ public:
 	{
 		return m_rollingFriction;
 	}
-
+    void	setSpinningFriction(btScalar frict)
+    {
+        m_updateRevision++;
+        m_spinningFriction = frict;
+    }
+    btScalar	getSpinningFriction() const
+    {
+        return m_spinningFriction;
+    }
     void	setContactStiffnessAndDamping(btScalar stiffness, btScalar damping)
 	{
 		m_updateRevision++;

src/BulletCollision/CollisionDispatch/btManifoldResult.cpp

@@ -24,7 +24,6 @@ ContactAddedCallback		gContactAddedCallback=0;
 
 
 
-///User can override this material combiner by implementing gContactAddedCallback and setting body0->m_collisionFlags |= btCollisionObject::customMaterialCallback;
 btScalar	btManifoldResult::calculateCombinedRollingFriction(const btCollisionObject* body0,const btCollisionObject* body1)
 {
 	btScalar friction = body0->getRollingFriction() * body1->getFriction() + body1->getRollingFriction() * body0->getFriction();
@@ -38,6 +37,17 @@ btScalar	btManifoldResult::calculateCombinedRollingFriction(const btCollisionObj
 
 }
 
+btScalar	btManifoldResult::calculateCombinedSpinningFriction(const btCollisionObject* body0,const btCollisionObject* body1)
+{
+    btScalar friction = body0->getSpinningFriction() * body1->getFriction() + body1->getSpinningFriction() * body0->getFriction();
+    
+    const btScalar MAX_FRICTION  = btScalar(10.);
+    if (friction < -MAX_FRICTION)
+        friction = -MAX_FRICTION;
+    if (friction > MAX_FRICTION)
+        friction = MAX_FRICTION;
+    return friction;
+}
 
 ///User can override this material combiner by implementing gContactAddedCallback and setting body0->m_collisionFlags |= btCollisionObject::customMaterialCallback;
 btScalar	btManifoldResult::calculateCombinedFriction(const btCollisionObject* body0,const btCollisionObject* body1)

src/BulletCollision/CollisionDispatch/btManifoldResult.h

@@ -146,7 +146,8 @@ public:
 	static btScalar	calculateCombinedRestitution(const btCollisionObject* body0,const btCollisionObject* body1);
 	static btScalar	calculateCombinedFriction(const btCollisionObject* body0,const btCollisionObject* body1);
 	static btScalar calculateCombinedRollingFriction(const btCollisionObject* body0,const btCollisionObject* body1);
-	static btScalar calculateCombinedContactDamping(const btCollisionObject* body0,const btCollisionObject* body1);
+    static btScalar calculateCombinedSpinningFriction(const btCollisionObject* body0,const btCollisionObject* body1);
+    static btScalar calculateCombinedContactDamping(const btCollisionObject* body0,const btCollisionObject* body1);
 	static btScalar calculateCombinedContactStiffness(const btCollisionObject* body0,const btCollisionObject* body1);
 };
 

src/BulletCollision/NarrowPhaseCollision/btManifoldPoint.h

@@ -72,7 +72,8 @@ class btManifoldPoint
 					m_distance1( distance ),
 					m_combinedFriction(btScalar(0.)),
 					m_combinedRollingFriction(btScalar(0.)),
-					m_combinedRestitution(btScalar(0.)),
+                    m_combinedSpinningFriction(btScalar(0.)),
+                    m_combinedRestitution(btScalar(0.)),
 					m_userPersistentData(0),
 					m_contactPointFlags(0),
 					m_appliedImpulse(0.f),
@@ -99,8 +100,9 @@ class btManifoldPoint
 		
 			btScalar	m_distance1;
 			btScalar	m_combinedFriction;
-			btScalar	m_combinedRollingFriction;
+			btScalar	m_combinedRollingFriction;//torsional friction orthogonal to contact normal, useful to make spheres stop rolling forever
-			btScalar	m_combinedRestitution;
+            btScalar	m_combinedSpinningFriction;//torsional friction around contact normal, useful for grasping objects
+            btScalar	m_combinedRestitution;
 
 			//BP mod, store contact triangles.
 			int			m_partId0;

src/BulletDynamics/Dynamics/btRigidBody.cpp

@@ -79,6 +79,8 @@ void	btRigidBody::setupRigidBody(const btRigidBody::btRigidBodyConstructionInfo&
 	//moved to btCollisionObject
 	m_friction = constructionInfo.m_friction;
 	m_rollingFriction = constructionInfo.m_rollingFriction;
+    m_spinningFriction = constructionInfo.m_spinningFriction;
+    
 	m_restitution = constructionInfo.m_restitution;
 
 	setCollisionShape( constructionInfo.m_collisionShape );

src/BulletDynamics/Dynamics/btRigidBody.h

@@ -135,6 +135,8 @@ public:
 		///the m_rollingFriction prevents rounded shapes, such as spheres, cylinders and capsules from rolling forever.
 		///See Bullet/Demos/RollingFrictionDemo for usage
 		btScalar			m_rollingFriction;
+        btScalar			m_spinningFriction;//torsional friction around contact normal
+        
 		///best simulation results using zero restitution.
 		btScalar			m_restitution;
 
@@ -158,6 +160,7 @@ public:
 			m_angularDamping(btScalar(0.)),
 			m_friction(btScalar(0.5)),
 			m_rollingFriction(btScalar(0)),
+            m_spinningFriction(btScalar(0)),
 			m_restitution(btScalar(0.)),
 			m_linearSleepingThreshold(btScalar(0.8)),
 			m_angularSleepingThreshold(btScalar(1.f)),