enable btGearConstraint, expose 'changeDynamics' for gearRatio, only works for maximalCoordinates rigid bodies.

See examples\pybullet\examples\mimicJointConstraint.py

examples/SharedMemory/PhysicsClientC_API.cpp

@@ -1704,7 +1704,18 @@ int b3InitChangeUserConstraintSetMaxForce(b3SharedMemoryCommandHandle commandHan
 
 	return 0;
 }
+int b3InitChangeUserConstraintSetGearRatio(b3SharedMemoryCommandHandle commandHandle, double gearRatio)
+{
+	struct SharedMemoryCommand* command = (struct SharedMemoryCommand*) commandHandle;
+	b3Assert(command);
+	b3Assert(command->m_type == CMD_USER_CONSTRAINT);
+	b3Assert(command->m_updateFlags & USER_CONSTRAINT_CHANGE_CONSTRAINT);
+	
+	command->m_updateFlags |=USER_CONSTRAINT_CHANGE_GEAR_RATIO;
+	command->m_userConstraintArguments.m_gearRatio = gearRatio;
 
+	return 0;
+}
 
 b3SharedMemoryCommandHandle  b3InitRemoveUserConstraintCommand(b3PhysicsClientHandle physClient, int userConstraintUniqueId)
 {

examples/SharedMemory/PhysicsClientC_API.h

@@ -102,7 +102,9 @@ b3SharedMemoryCommandHandle  b3InitChangeUserConstraintCommand(b3PhysicsClientHa
 int b3InitChangeUserConstraintSetPivotInB(b3SharedMemoryCommandHandle commandHandle, double jointChildPivot[3]);
 int b3InitChangeUserConstraintSetFrameInB(b3SharedMemoryCommandHandle commandHandle, double jointChildFrameOrn[4]);
 int b3InitChangeUserConstraintSetMaxForce(b3SharedMemoryCommandHandle commandHandle, double maxAppliedForce);
-	
+int b3InitChangeUserConstraintSetGearRatio(b3SharedMemoryCommandHandle commandHandle, double gearRatio);
+
+
 b3SharedMemoryCommandHandle  b3InitRemoveUserConstraintCommand(b3PhysicsClientHandle physClient, int userConstraintUniqueId);
 
 int b3GetNumUserConstraints(b3PhysicsClientHandle physClient);

examples/SharedMemory/PhysicsServerCommandProcessor.cpp

@@ -5877,7 +5877,48 @@ bool PhysicsServerCommandProcessor::processCommand(const struct SharedMemoryComm
 							
 								}
 							}
+						}
+						else
+						{
+							InteralBodyData* childBody = clientCmd.m_userConstraintArguments.m_childBodyIndex>=0 ? m_data->m_bodyHandles.getHandle(clientCmd.m_userConstraintArguments.m_childBodyIndex):0;
+						
+							if (parentBody && childBody)
+							{
+								if (parentBody->m_rigidBody)
+								{
+									if (clientCmd.m_userConstraintArguments.m_jointType == eGearType)
+									{
+										btRigidBody* childRb = childBody->m_rigidBody;
+										if (childRb)
+										{
+											btVector3 axisA(clientCmd.m_userConstraintArguments.m_jointAxis[0],
+												clientCmd.m_userConstraintArguments.m_jointAxis[1],
+												clientCmd.m_userConstraintArguments.m_jointAxis[2]);
+
+											//for now we use the same local axis for both objects
+											btVector3 axisB(clientCmd.m_userConstraintArguments.m_jointAxis[0],
+												clientCmd.m_userConstraintArguments.m_jointAxis[1],
+												clientCmd.m_userConstraintArguments.m_jointAxis[2]);
+
+											btScalar ratio=1;
+											btGearConstraint* gear = new btGearConstraint(*parentBody->m_rigidBody,*childRb, axisA,axisB,ratio);
+											m_data->m_dynamicsWorld->addConstraint(gear,true);
+
+											InteralUserConstraintData userConstraintData;
+											userConstraintData.m_rbConstraint = gear;
+											int uid = m_data->m_userConstraintUIDGenerator++;
+											serverCmd.m_userConstraintResultArgs = clientCmd.m_userConstraintArguments;
+											serverCmd.m_userConstraintResultArgs.m_userConstraintUniqueId = uid;
+											serverCmd.m_userConstraintResultArgs.m_maxAppliedForce = defaultMaxForce;
+											userConstraintData.m_userConstraintData = serverCmd.m_userConstraintResultArgs;
+											m_data->m_userConstraints.insert(uid,userConstraintData);
+
+											serverCmd.m_type = CMD_USER_CONSTRAINT_COMPLETED;
+										}
+									}
+								}
 							}
+						}
 					}
 
 					if (clientCmd.m_updateFlags & USER_CONSTRAINT_CHANGE_CONSTRAINT)
@@ -5921,7 +5962,14 @@ bool PhysicsServerCommandProcessor::processCommand(const struct SharedMemoryComm
 							}
 							if (userConstraintPtr->m_rbConstraint)
 							{
-								//todo
+								if (clientCmd.m_updateFlags & USER_CONSTRAINT_CHANGE_GEAR_RATIO)
+								{
+									if (userConstraintPtr->m_rbConstraint->getObjectType()==GEAR_CONSTRAINT_TYPE)
+									{
+										btGearConstraint* gear = (btGearConstraint*) userConstraintPtr->m_rbConstraint;
+										gear->setRatio(clientCmd.m_userConstraintArguments.m_gearRatio);
+									}
+								}
 							}
 							serverCmd.m_userConstraintResultArgs = clientCmd.m_userConstraintArguments;
 							serverCmd.m_userConstraintResultArgs.m_userConstraintUniqueId = userConstraintUidChange;
@@ -5944,7 +5992,9 @@ bool PhysicsServerCommandProcessor::processCommand(const struct SharedMemoryComm
 							}
 							if (userConstraintPtr->m_rbConstraint)
 							{
-
+								m_data->m_dynamicsWorld->removeConstraint(userConstraintPtr->m_rbConstraint);
+								delete userConstraintPtr->m_rbConstraint;
+								m_data->m_userConstraints.remove(userConstraintUidRemove);	
 							}
 							serverCmd.m_userConstraintResultArgs.m_userConstraintUniqueId = userConstraintUidRemove;
 							serverCmd.m_type = CMD_REMOVE_USER_CONSTRAINT_COMPLETED;

examples/SharedMemory/SharedMemoryCommands.h

@@ -627,7 +627,7 @@ enum EnumUserConstraintFlags
 	USER_CONSTRAINT_CHANGE_FRAME_ORN_IN_B=16,
 	USER_CONSTRAINT_CHANGE_MAX_FORCE=32,
 	USER_CONSTRAINT_REQUEST_INFO=64,
-	
+	USER_CONSTRAINT_CHANGE_GEAR_RATIO=128,	
 };
 
 enum EnumBodyChangeFlags

examples/SharedMemory/SharedMemoryPublic.h

@@ -184,6 +184,7 @@ enum JointType {
 	ePlanarType = 3,
 	eFixedType = 4,
 	ePoint2PointType = 5,
+	eGearType=6
 };
 
 
@@ -227,6 +228,8 @@ struct b3UserConstraint
     int m_jointType;
     double m_maxAppliedForce;
     int m_userConstraintUniqueId;
+	double m_gearRatio;
+
 };
 
 struct b3BodyInfo

examples/pybullet/examples/mimicJointConstraint.py

@@ -0,0 +1,16 @@
+#mimic joint currently only works for 'maximal coordinate' rigid bodies
+#one way to use it would be to attach maximal coordinate rigid bodies to multibody links using
+#fixed constraints
+
+import pybullet as p
+import time
+p.connect(p.GUI)
+wheelA = p.loadURDF("wheel.urdf",[0,0,0],useMaximalCoordinates=1)
+wheelB = p.loadURDF("wheel.urdf",[0,0,1],useMaximalCoordinates=1)
+c = p.createConstraint(wheelA,-1,wheelB,-1,jointType=p.JOINT_GEAR,jointAxis =[0,1,0],parentFramePosition=[0,0,0],childFramePosition=[0,0,0])
+p.changeConstraint(c,gearRatio=-0.1)
+p.setRealTimeSimulation(1)
+while(1):
+	time.sleep(0.01)
+p.removeConstraint(c)
+	

examples/pybullet/pybullet.c

@@ -4608,7 +4608,7 @@ static PyObject* pybullet_getClosestPointData(PyObject* self, PyObject* args, Py
 
 static PyObject* pybullet_changeUserConstraint(PyObject* self, PyObject* args, PyObject* keywds)
 {
-	static char* kwlist[] = {"userConstraintUniqueId", "jointChildPivot", "jointChildFrameOrientation", "maxForce", "physicsClientId", NULL};
+	static char* kwlist[] = {"userConstraintUniqueId", "jointChildPivot", "jointChildFrameOrientation", "maxForce", "gearRatio", "physicsClientId", NULL};
 	int userConstraintUniqueId = -1;
 	b3SharedMemoryCommandHandle commandHandle;
 	b3SharedMemoryStatusHandle statusHandle;
@@ -4620,8 +4620,8 @@ static PyObject* pybullet_changeUserConstraint(PyObject* self, PyObject* args, P
 	double jointChildPivot[3];
 	double jointChildFrameOrn[4];
 	double maxForce = -1;
-
+	double gearRatio = 0;
-	if (!PyArg_ParseTupleAndKeywords(args, keywds, "i|OOdi", kwlist, &userConstraintUniqueId, &jointChildPivotObj, &jointChildFrameOrnObj, &maxForce, &physicsClientId))
+	if (!PyArg_ParseTupleAndKeywords(args, keywds, "i|OOddi", kwlist, &userConstraintUniqueId, &jointChildPivotObj, &jointChildFrameOrnObj, &maxForce, &gearRatio, &physicsClientId))
 	{
 		return NULL;
 	}
@@ -4647,7 +4647,10 @@ static PyObject* pybullet_changeUserConstraint(PyObject* self, PyObject* args, P
 	{
 		b3InitChangeUserConstraintSetMaxForce(commandHandle, maxForce);
 	}
-
+	if (gearRatio!=0)
+	{
+		b3InitChangeUserConstraintSetGearRatio(commandHandle,gearRatio);
+	}
 	statusHandle = b3SubmitClientCommandAndWaitStatus(sm, commandHandle);
 	statusType = b3GetStatusType(statusHandle);
 	Py_INCREF(Py_None);
@@ -6769,6 +6772,7 @@ initpybullet(void)
 	PyModule_AddIntConstant(m, "JOINT_PLANAR", ePlanarType);            // user read
 	PyModule_AddIntConstant(m, "JOINT_FIXED", eFixedType);              // user read
 	PyModule_AddIntConstant(m, "JOINT_POINT2POINT", ePoint2PointType);  // user read
+	PyModule_AddIntConstant(m, "JOINT_GEAR", eGearType);  // user read
 
 	PyModule_AddIntConstant(m, "SENSOR_FORCE_TORQUE", eSensorForceTorqueType);  // user read