mujoco

<mujoco model="contact net">
  <statistic meansize="0.05"/>

  <default>
    <geom condim="6"/>
  </default>

  <worldbody>
    <light pos="0 0 3"/>
    <geom name="floor" type="plane" size=".5 1 .01"/>

    <body name="b1" pos="0 0 .4" euler="5 4 3">
      <freejoint/>
      <geom type="box" pos="0 0 .06" size=".15 .15 .03" rgba=".8 .2 .1 .2"/>
      <geom type="box" pos="-.05 0 .005" size=".04 .04 .025" rgba=".8 .2 .1 1" euler="1 1 1"/>
      <geom size=".05" pos=".1 -.1 .04" rgba=".8 .2 .1 1"/>
    </body>

    <body name="b2" pos="0 0 .2">
      <joint type="ball" springdamper="0.1 1"/>
      <geom type="box" size=".2 .2 .05" rgba=".8 .2 .1 1"/>
      <geom size=".05" pos=".1 .1 .05" rgba=".8 .2 .1 1"/>
      <geom type="box" size=".05 .05 .01" pos=".1 -.1 .06" rgba=".8 .2 .1 1" euler="2 2 2"/>
    </body>
  </worldbody>

  <sensor>
    <contact name="net12" body1="b1" body2="b2" data="force torque pos" reduce="netforce"/>
    <contact name="net21" body1="b2" body2="b1" data="force torque pos" reduce="netforce"/>
  </sensor>
</mujoco>