fixed implicit fixed joint.

Author: micahpearlman

Runtime/Scripts/Document/ZOSimOccurrence.cs

@@ -1297,7 +1297,7 @@ protected void BuildURDFJoints(XElement robot, ZOSimOccurrence parent, Matrix4x4
                     origin.SetAttributeValue("rpy", rpy.ToXMLString());
                     jointX.Add(origin);
 
-                    URDFJoint joint = new URDFJoint(this, parent, jointMatrix.Position(), jointMatrix.Position());
+                    URDFJoint joint = new URDFJoint(this, parent, jointMatrix.Position(), Vector3.zero);
                     joints.Add(joint);