mujoco

<mujoco>
  <custom>
    <numeric name="duration" data="6.5"/>
  </custom>

  <option viscosity="60" gravity="0 0 -1">
    <flag energy="enable" sleep="enable" constraint="disable" contact="disable"/>
  </option>

  <worldbody>
    <body gravcomp="1">
      <geom type="box" size=".2 .2 .2"/>
      <freejoint/>
      <body pos="-.4 0 0" gravcomp="1">
        <geom type="cylinder" size="0.1" fromto="0 0 0 0 0 1"/>
        <joint type="slide" axis="0 0 1" springref="0.2" springdamper="0.1 1"/>
      </body>
    </body>

    <body pos="1 0 0">
      <geom type="box" size=".2 .2 .2"/>
      <body>
        <joint axis="1 0 0" springdamper="0.1 1"/>
        <geom type="capsule" size="0.1" fromto="0 0 0 0 0 1"/>
        <site name="1" pos="0 -.1 .5" size=".03" rgba="1 0 0 1"/>
        <body pos="0 0 1">
          <joint axis="1 0 0" springref="45" springdamper="0.1 1"/>
          <geom type="capsule" size="0.1" fromto="0 0 0 0 0 1"/>
          <site name="2" pos="0 -.1 .5" size=".03" rgba="1 0 0 1"/>
        </body>
      </body>
    </body>

    <body pos="2 0 0">
      <geom size=".3"/>
      <joint type="ball" stiffness="300" damping="30"/>
      <body name="angmom" pos=".2 0 0">
        <geom type="cylinder" size="0.1" fromto="0 0 0 0 0 1"/>
        <joint type="slide" axis="0 0 1" springref="0.2" stiffness="1000" damping="100"/>
      </body>
    </body>
  </worldbody>

  <tendon>
    <spatial width="0.01" armature="1">
      <site site="1"/>
      <site site="2"/>
    </spatial>
  </tendon>

  <sensor>
    <subtreeangmom body="angmom"/>
  </sensor>
</mujoco>