added some comments

bullet/physic.hpp

@@ -90,6 +90,10 @@ namespace Physic
 
         std::string mName;
 
+        /**
+        *NPC scenenode is located on there feet, and you can't simply translate a btShape, so this vector is used
+        *each time get/setposition is called.
+        */
         btVector3 mTranslation;
     };