mujoco

<mujoco model="fixed_site">
  <worldbody>
    <body>
      <joint name="joint0" type="hinge" axis="0 1 0"/>
      <geom type="capsule" size="0.05 0.5" fromto="0 0 0 0.5 0 0"/>
      <site name="site0" pos="0.25 0 0.1" size="0.025"/>
      <body pos="0.5 0 0">
        <joint name="joint1" type="hinge" axis="0 1 0"/>
        <geom type="capsule" size="0.05 0.5" fromto="0 0 0 0.5 0 0"/>
        <site name="site1" pos="0.25 0 0.1" size="0.025"/>
        <body pos="0.5 0 0">
          <joint name="joint2" type="hinge" axis="0 1 0"/>
          <geom type="capsule" size="0.05 0.5" fromto="0 0 0 0.5 0 0"/>
          <site name="site2" pos="0.25 0 0.1" size="0.025"/>
        </body>
      </body>
    </body>
  </worldbody>
  <tendon>
    <spatial name="spatial0" width="0.0125">
      <site site="site0"/>
      <site site="site1"/>
      <site site="site2"/>
    </spatial>
    <spatial name="spatial1" width="0.0125" actuatorfrclimited="true" actuatorfrcrange="-1 1">
      <site site="site1"/>
      <site site="site2"/>
    </spatial>
    <fixed name="fixed0" actuatorfrclimited="true" actuatorfrcrange="-10 10">
      <joint joint="joint0" coef=".1"/>
      <joint joint="joint1" coef=".2"/>
      <joint joint="joint2" coef=".3"/>
    </fixed>
    <fixed name="fixed1" actuatorfrclimited="true" actuatorfrcrange="0 1">
      <joint joint="joint0" coef=".1"/>
      <joint joint="joint2" coef=".3"/>
    </fixed>
  </tendon>
  <actuator>
    <motor tendon="spatial0"/>
    <motor tendon="spatial0"/>
    <motor tendon="spatial0"/>
    <motor tendon="spatial1"/>
    <motor tendon="spatial1"/>
    <motor tendon="fixed0"/>
    <motor tendon="fixed1"/>
    <motor tendon="fixed1"/>
  </actuator>
  <sensor>
    <tendonactuatorfrc tendon="spatial0"/>
    <tendonactuatorfrc tendon="spatial1"/>
    <tendonactuatorfrc tendon="fixed0"/>
    <tendonactuatorfrc tendon="fixed1"/>
  </sensor>
</mujoco>