<mujoco model="acrobot">
  <worldbody>
    <geom name="Link1_pivot" type="sphere" size="0.125" rgba="0 0 1 1" mass="0"/>
    <body name="Link1" pos="0 0 0">
      <joint name="shoulder" type="hinge" axis="0 1 0" damping="0.5"/>
      <geom name="Link1" type="cylinder" fromto="0 0 0.05 0 0 -1.05" size="0.05" rgba="0 1 0 1" mass="1"/>
      <body name="Link2" pos="0 0 -1">
        <joint name="elbow" type="hinge" axis="0 1 0" damping="0.5"/>
        <geom name="Link2" type="cylinder" fromto="0 0 0.05 0 0 -2.05" size="0.05" rgba="1 0 0 1" mass="1"/>
      </body>
    </body>
  </worldbody>

  <actuator>
    <motor name="elbow" joint="elbow"/>
  </actuator>
</mujoco>
