assets/mjcf/base.xml

<?xml version="1.0" ?>
<mujoco model="base">
  <asset>
    <mesh name="mesh_base" file="../obj/base.obj"/>
  </asset>
  <worldbody>
    <body name="base">
      <geom name="base_geom" type="mesh" mesh="mesh_base"/>
    </body>
  </worldbody>
</mujoco>