1) Is there any mechanism to simulate gears/pulleys in URDF/Gazebo? For
example, when object A rotates, object B rotates twice as much.

2) Where are the xmlschema of yesteryear? It appears that most URDF files
reference namespaces at http://playerstage.sourceforge.net/gazebo/xmlschema/,
which now returns a 404.

Thanks,
David!!