Moved the 'btRigidBody::clearForce' to the end of the stepSimulation, instead of in each substep.

Should help with this issue, reported here: http://www.bulletphysics.com/Bullet/phpBB3/viewtopic.php?f=9&t=1601
We can optionally leave out the 'clearForces'.
Thanks everyone for the discussion.

src/BulletDynamics/Dynamics/btDiscreteDynamicsWorld.cpp

@@ -196,6 +196,21 @@ void	btDiscreteDynamicsWorld::debugDrawWorld()
 	}
 }
 
+void	btDiscreteDynamicsWorld::clearForces()
+{
+	//todo: iterate over awake simulation islands!
+	for ( int i=0;i<m_collisionObjects.size();i++)
+	{
+		btCollisionObject* colObj = m_collisionObjects[i];
+		
+		btRigidBody* body = btRigidBody::upcast(colObj);
+		if (body)
+		{
+			body->clearForces();
+		}
+	}
+}	
+
 void	btDiscreteDynamicsWorld::synchronizeMotionStates()
 {
 	{
@@ -292,6 +307,8 @@ int	btDiscreteDynamicsWorld::stepSimulation( btScalar timeStep,int maxSubSteps,
 
 	synchronizeMotionStates();
 
+	clearForces();
+
 	CProfileManager::Increment_Frame_Counter();
 	
 	return numSimulationSubSteps;

src/BulletDynamics/Dynamics/btDiscreteDynamicsWorld.h

@@ -150,6 +150,9 @@ public:
 	}
 
 	
+	virtual void	clearForces();
+
+
 };
 
 #endif //BT_DISCRETE_DYNAMICS_WORLD_H

src/BulletDynamics/Dynamics/btDynamicsWorld.h

@@ -78,6 +78,9 @@ class btDynamicsWorld : public btCollisionWorld
 
 		virtual btDynamicsWorldType	getWorldType() const=0;
 
+		virtual void	clearForces() = 0;
+
+
 };
 
 #endif //BT_DYNAMICS_WORLD_H

src/BulletDynamics/Dynamics/btRigidBody.cpp

@@ -290,7 +290,6 @@ void btRigidBody::integrateVelocities(btScalar step)
 		m_angularVelocity *= (MAX_ANGVEL/step) /angvel;
 	}
 
-	clearForces();
 }
 
 btQuaternion btRigidBody::getOrientation() const

src/BulletDynamics/Dynamics/btSimpleDynamicsWorld.cpp

@@ -85,10 +85,27 @@ int		btSimpleDynamicsWorld::stepSimulation( btScalar timeStep,int maxSubSteps, b
 
 	synchronizeMotionStates();
 
+	clearForces();
+
 	return 1;
 
 }
 
+void	btSimpleDynamicsWorld::clearForces()
+{
+	//todo: iterate over awake simulation islands!
+	for ( int i=0;i<m_collisionObjects.size();i++)
+	{
+		btCollisionObject* colObj = m_collisionObjects[i];
+		
+		btRigidBody* body = btRigidBody::upcast(colObj);
+		if (body)
+		{
+			body->clearForces();
+		}
+	}
+}	
+
 
 void	btSimpleDynamicsWorld::setGravity(const btVector3& gravity)
 {

src/BulletDynamics/Dynamics/btSimpleDynamicsWorld.h

@@ -69,6 +69,8 @@ public:
 		return BT_SIMPLE_DYNAMICS_WORLD;
 	}
 
+	virtual void	clearForces();
+
 };
 
 #endif //BT_SIMPLE_DYNAMICS_WORLD_H