add TestHingeTorque example using btRigidBody and btHingeConstraint, setup is similar to TestJointTorque using btMultiBody and a revolute joint.

examples/Constraints/TestHingeTorque.cpp

@@ -0,0 +1,153 @@
+#include "TestHingeTorque.h"
+
+
+#include "../CommonInterfaces/CommonRigidBodyBase.h"
+#include "../CommonInterfaces/CommonParameterInterface.h"
+
+
+
+struct TestHingeTorque : public CommonRigidBodyBase
+{
+    bool m_once;
+    
+	TestHingeTorque(struct GUIHelperInterface* helper);
+	virtual ~ TestHingeTorque();
+	virtual void initPhysics();
+
+	virtual void stepSimulation(float deltaTime);
+
+	
+	virtual void resetCamera()
+	{
+    
+        float dist = 5;
+        float pitch = 270;
+        float yaw = 21;
+        float targetPos[3]={-1.34,3.4,-0.44};
+        m_guiHelper->resetCamera(dist,pitch,yaw,targetPos[0],targetPos[1],targetPos[2]);
+	}
+	
+
+};
+
+TestHingeTorque::TestHingeTorque(struct GUIHelperInterface* helper)
+:CommonRigidBodyBase(helper),
+m_once(true)
+{
+}
+TestHingeTorque::~ TestHingeTorque()
+{
+}
+
+
+void TestHingeTorque::stepSimulation(float deltaTime)
+{
+    if (m_once)
+    {
+        m_once=false;
+        btHingeConstraint* hinge = (btHingeConstraint*)m_dynamicsWorld->getConstraint(0);
+        
+        btRigidBody& bodyA = hinge->getRigidBodyA();
+        btTransform trA = bodyA.getWorldTransform();
+        btVector3 hingeAxisInWorld = trA.getBasis()*hinge->getFrameOffsetA().getBasis().getColumn(2);
+        hinge->getRigidBodyA().applyTorque(-hingeAxisInWorld*10);
+        hinge->getRigidBodyB().applyTorque(hingeAxisInWorld*10);
+        
+    }
+    
+    m_dynamicsWorld->stepSimulation(1./60,0);
+    btRigidBody* base = btRigidBody::upcast(m_dynamicsWorld->getCollisionObjectArray()[0]);
+    
+    b3Printf("base angvel = %f,%f,%f",base->getAngularVelocity()[0],
+             base->getAngularVelocity()[1],
+             
+             base->getAngularVelocity()[2]);
+    
+    btRigidBody* child = btRigidBody::upcast(m_dynamicsWorld->getCollisionObjectArray()[1]);
+    
+    b3Printf("child angvel = %f,%f,%f",child->getAngularVelocity()[0],
+             child->getAngularVelocity()[1],
+
+             child->getAngularVelocity()[2]);
+    
+    //CommonRigidBodyBase::stepSimulation(deltaTime);
+}
+
+
+
+void TestHingeTorque::initPhysics()
+{
+	m_guiHelper->setUpAxis(2);
+
+	createEmptyDynamicsWorld();
+    m_dynamicsWorld->setGravity(btVector3(0,0,0));
+    
+	m_guiHelper->createPhysicsDebugDrawer(m_dynamicsWorld);
+	int mode = 	btIDebugDraw::DBG_DrawWireframe
+				+btIDebugDraw::DBG_DrawConstraints
+				+btIDebugDraw::DBG_DrawConstraintLimits;
+	m_dynamicsWorld->getDebugDrawer()->setDebugMode(mode);
+
+
+	{ // create a door using hinge constraint attached to the world
+        
+        int numLinks = 1;
+        bool spherical = false;					//set it ot false -to use 1DoF hinges instead of 3DoF sphericals
+        bool canSleep = false;
+        bool selfCollide = false;
+        btVector3 linkHalfExtents(0.05, 0.37, 0.1);
+        btVector3 baseHalfExtents(0.05, 0.37, 0.1);
+
+        btBoxShape* baseBox = new btBoxShape(baseHalfExtents);
+        btVector3 basePosition = btVector3(-0.4f, 3.f, 0.f);
+        btTransform baseWorldTrans;
+        baseWorldTrans.setIdentity();
+        baseWorldTrans.setOrigin(basePosition);
+        
+        //mbC->forceMultiDof();							//if !spherical, you can comment this line to check the 1DoF algorithm
+        //init the base
+        btVector3 baseInertiaDiag(0.f, 0.f, 0.f);
+        float baseMass = 1.f;
+        float linkMass = 1.f;
+        
+        btRigidBody* base = createRigidBody(baseMass,baseWorldTrans,baseBox);
+        m_dynamicsWorld->removeRigidBody(base);
+        base->setDamping(0,0);
+        m_dynamicsWorld->addRigidBody(base,0,0);
+        btBoxShape* linkBox = new btBoxShape(linkHalfExtents);
+        btRigidBody* prevBody = base;
+        
+        for (int i=0;i<numLinks;i++)
+        {
+            btTransform linkTrans;
+            linkTrans = baseWorldTrans;
+            
+            linkTrans.setOrigin(basePosition-btVector3(0,linkHalfExtents[1]*2.f*(i+1),0));
+            
+            btRigidBody* linkBody = createRigidBody(linkMass,linkTrans,linkBox);
+            m_dynamicsWorld->removeRigidBody(linkBody);
+            m_dynamicsWorld->addRigidBody(linkBody,0,0);
+            linkBody->setDamping(0,0);
+            //create a hinge constraint
+            btVector3 pivotInA(0,-linkHalfExtents[1],0);
+            btVector3 pivotInB(0,linkHalfExtents[1],0);
+            btVector3 axisInA(1,0,0);
+            btVector3 axisInB(1,0,0);
+            bool useReferenceA = true;
+            btHingeConstraint* hinge = new btHingeConstraint(*prevBody,*linkBody,
+                                                             pivotInA,pivotInB,
+                                                             axisInA,axisInB,useReferenceA);
+            m_dynamicsWorld->addConstraint(hinge,true);
+            prevBody = linkBody;
+            
+        }
+       
+	}
+	
+	m_guiHelper->autogenerateGraphicsObjects(m_dynamicsWorld);
+}
+
+class CommonExampleInterface*    TestHingeTorqueCreateFunc(CommonExampleOptions& options)
+{
+	return new TestHingeTorque(options.m_guiHelper);
+}

examples/Constraints/TestHingeTorque.h

@@ -0,0 +1,7 @@
+#ifndef TEST_HINGE_TORQUE_H
+#define TEST_HINGE_TORQUE_H
+
+class CommonExampleInterface*    TestHingeTorqueCreateFunc(struct CommonExampleOptions& options);
+
+#endif //TEST_HINGE_TORQUE_H
+

examples/ExampleBrowser/CMakeLists.txt

@@ -97,6 +97,8 @@ SET(App_ExampleBrowser_SRCS
   ../MultiBody/TestJointTorqueSetup.h
   ../MultiBody/MultiDofDemo.cpp
   ../MultiBody/MultiDofDemo.h
+  ../Constraints/TestHingeTorque.cpp
+  ../Constraints/TestHingeTorque.h
   ../Constraints/ConstraintDemo.cpp
   ../Constraints/ConstraintDemo.h
   ../Constraints/Dof6Spring2Setup.cpp

examples/ExampleBrowser/ExampleEntries.cpp

@@ -32,6 +32,8 @@
 #include "../RollingFrictionDemo/RollingFrictionDemo.h"
 #include "../SharedMemory/PhysicsServer.h"
 #include "../SharedMemory/PhysicsClient.h"
+#include "../Constraints/TestHingeTorque.h"
+
 
 #ifdef ENABLE_LUA
 #include "../LuaDemo/LuaPhysicsSetup.h"
@@ -79,6 +81,8 @@ static ExampleEntry gDefaultExamples[]=
 				 AllConstraintCreateFunc),
 
 	ExampleEntry(1,"Motorized Hinge","Use of a btHingeConstraint. You can adjust the first slider to change the target velocity, and the second slider to adjust the maximum impulse applied to reach the target velocity. Note that the hinge angle can reach beyond -360 and 360 degrees.", ConstraintCreateFunc),
+    ExampleEntry(1,"TestHingeTorque", "Apply a torque in the hinge axis. This example uses a btHingeConstraint and btRigidBody. The setup is similar to the multi body example TestJointTorque.",
+                 TestHingeTorqueCreateFunc),
     
 //	ExampleEntry(0,"What's new in 2.83"),
 	
@@ -94,7 +98,7 @@ static ExampleEntry gDefaultExamples[]=
 
 	ExampleEntry(0,"MultiBody"),
 	ExampleEntry(1,"MultiDofCreateFunc","Create a basic btMultiBody with 3-DOF spherical joints (mobilizers). The demo uses a fixed base or a floating base at restart.", MultiDofCreateFunc),
-	ExampleEntry(1,"TestJointTorque","Apply a torque to a btMultiBody with 1-DOF joints (mobilizers).", TestJointTorqueCreateFunc),
+	ExampleEntry(1,"TestJointTorque","Apply a torque to a btMultiBody with 1-DOF joints (mobilizers). This setup is similar to API/TestHingeTorque.", TestJointTorqueCreateFunc),
 	
 	
 #ifdef INCLUDE_CLOTH_DEMOS

examples/MultiBody/TestJointTorqueSetup.cpp

@@ -8,7 +8,7 @@
 struct TestJointTorqueSetup : public CommonMultiBodyBase
 {
     btMultiBody* m_multiBody;
-
+    bool m_once;
 public:
 
     TestJointTorqueSetup(struct GUIHelperInterface* helper);
@@ -31,7 +31,8 @@ public:
 };
 
 TestJointTorqueSetup::TestJointTorqueSetup(struct GUIHelperInterface* helper)
-:CommonMultiBodyBase(helper)
+:CommonMultiBodyBase(helper),
+m_once(true)
 {
 }
 
@@ -88,10 +89,10 @@ void TestJointTorqueSetup::initPhysics()
         }
 
     {
-        bool floating = false;
-        bool damping = true;
-        bool gyro = true;
-        int numLinks = 5;
+        bool floating = true;
+        bool damping = false;
+        bool gyro = false;
+        int numLinks = 1;
         bool spherical = false;					//set it ot false -to use 1DoF hinges instead of 3DoF sphericals
         bool canSleep = false;
         bool selfCollide = false;
@@ -173,7 +174,7 @@ void TestJointTorqueSetup::initPhysics()
         //gravity[upAxis] = -9.81;
         m_dynamicsWorld->setGravity(gravity);
         //////////////////////////////////////////////
-        if(numLinks > 0)
+        if(0)//numLinks > 0)
         {
             btScalar q0 = 45.f * SIMD_PI/ 180.f;
             if(!spherical)
@@ -275,8 +276,27 @@ void TestJointTorqueSetup::initPhysics()
 
 void TestJointTorqueSetup::stepSimulation(float deltaTime)
 {
-    m_multiBody->addJointTorque(0, 10.0);
-    m_dynamicsWorld->stepSimulation(deltaTime);
+    if (m_once)
+    {
+       m_once=false;
+        m_multiBody->addJointTorque(0, 10.0);
+    
+        btScalar torque = m_multiBody->getJointTorque(0);
+        b3Printf("t = %f,%f,%f\n",torque,torque,torque);//[0],torque[1],torque[2]);
+    }
+    
+    m_dynamicsWorld->stepSimulation(1./60,0);
+    b3Printf("base angvel = %f,%f,%f",m_multiBody->getBaseOmega()[0],
+             m_multiBody->getBaseOmega()[1],
+             m_multiBody->getBaseOmega()[2]
+             );
+    
+    btScalar jointVel =m_multiBody->getJointVel(0);
+    
+    b3Printf("child angvel = %f",jointVel);
+    
+    
+    
 }
 
 

src/BulletDynamics/Featherstone/btMultiBodyLink.h

@@ -123,7 +123,10 @@ struct btMultibodyLink
     btVector3 m_appliedTorque;   // In WORLD frame
 
 	btScalar m_jointPos[7];
-	btScalar m_jointTorque[6];			//TODO
+    
+    //m_jointTorque is the joint torque applied by the user using 'addJointTorque'.
+    //It gets set to zero after each internal stepSimulation call
+	btScalar m_jointTorque[6];
     
 	class btMultiBodyLinkCollider* m_collider;
 	int m_flags;