mujoco

<mujoco model="contact subtree">
  <worldbody>
    <light pos="0 0 5"/>
    <geom name="floor" type="plane" size="2 2 .01"/>
    <body name="thigh" pos="-1 0 .1">
      <joint type="slide"/>
      <geom type="capsule" size=".1" fromto="0 0 0 .5 0 0"/>
      <body name="shin" pos=".7 0 0">
        <joint axis="0 1 0"/>
        <geom type="capsule" size=".1" fromto="0 0 0 0 0 .5"/>
        <body name="foot" pos="0 0 .7">
          <joint axis="0 1 0"/>
          <geom type="capsule" size=".1" fromto="0 0 0 -.7 0 0"/>
        </body>
      </body>
    </body>
  </worldbody>

  <sensor>
    <contact name="all"/>
    <contact name="world" subtree1="world"/>
    <contact name="thigh" subtree1="thigh"/>
    <contact name="shin" subtree1="shin"/>
    <contact name="foot" subtree1="foot"/>
    <contact name="foot_w" subtree1="foot" body2="world"/>
    <contact name="foot_w2" subtree1="foot" subtree2="world"/>
  </sensor>
</mujoco>