mujoco

<mujoco>
  <option>
    <flag sleep="enable"/>
  </option>

  <worldbody>
    <light pos="0 -1 4"/>
    <geom type="plane" size="1.5 1.5 .01"/>

    <body pos=".3 0 .8">
      <joint name="1" axis="1 0 0" damping=".1"/>
      <geom type="box" size=".03 .1 .1"/>
    </body>

    <body pos=".7 0 .8">
      <joint name="2" axis="1 0 0" damping=".1"/>
      <geom type="box" size=".03 .1 .1"/>
    </body>

    <body pos=".5 0 .5">
      <geom type="box" size=".1 .1 .1"/>
      <site name="1" pos="-.1 0 0" size=".01" rgba="1 0 0 1"/>
    </body>

    <body pos="-.3 -.4 .5" euler="10 20 30">
      <freejoint/>
      <geom type="box" size=".1 .1 .1"/>
      <site name="2" pos="0 0 .1" size=".01" rgba="1 0 0 1" euler="0 -90 0"/>
      <site name="3" pos="0 -.1 0" size=".01" rgba="1 0 0 1" euler="0 0 -90"/>
    </body>

    <body pos=".7 -.3 .5">
      <freejoint/>
      <geom type="box" size=".1 .1 .1"/>
      <site name="4" pos="-.1 0 0" size=".01" rgba="1 0 0 1"/>
    </body>

    <body pos="-.3 0 .7">
      <joint axis="0 1 0" springdamper=".03 1"/>
      <geom type="capsule" size=".03" fromto="0 0 0 .2 0 0"/>
      <site name="5" pos=".1 0 .03" size=".01" rgba="1 0 0 1"/>
      <body pos=".2 0 0">
        <joint axis="0 1 0" springdamper=".03 1"/>
        <geom type="capsule" size=".03" fromto="0 0 0 0 0 .2"/>
        <body pos="0 0 .2">
          <joint axis="0 1 0" springdamper=".03 1"/>
          <geom type="capsule" size=".03" fromto="0 0 0 -.15 0 0"/>
          <site name="6" pos="-.18 0 0" size=".01" rgba="1 0 0 1"/>
        </body>
      </body>
    </body>
  </worldbody>

  <equality>
    <weld active="false" name="stat/dyn" site1="1" site2="2"/>
    <weld active="false" name="dyn/dyn" site1="3" site2="4"/>
    <connect active="false" name="self" site1="5" site2="6"/>
    <joint name="joint" joint1="1" joint2="2" polycoef="0 -2"/>
  </equality>
</mujoco>