mujoco

<mujoco>
  <option viscosity="30" integrator="implicit">
    <flag gravity="disable" constraint="disable" contact="disable" energy="enable" sleep="enable"/>
  </option>

  <worldbody>
    <replicate offset="0 0 2.5" count="7">
      <replicate offset="4 0 0" count="7">
        <replicate offset="0 2 0" count="7">
          <body sleep="init">
            <geom size=".4"/>
            <freejoint/>
            <body pos="-.4 0 0">
              <geom type="cylinder" size="0.1" fromto="0 0 0 0 0 1"/>
              <joint type="slide" axis="0 0 1" springref="0.2" stiffness="1000" damping="100"/>
            </body>
          </body>

          <body pos="1 0 0" sleep="init">
            <geom type="capsule" size="0.1" fromto="0 0 0 0 0 1"/>
            <joint axis="1 0 0" stiffness="300" damping="30"/>
            <body pos="0 0 1">
              <geom type="capsule" size="0.1" fromto="0 0 0 0 0 1"/>
              <joint axis="1 0 0" springref="45" stiffness="300" damping="30"/>
            </body>
          </body>

          <body pos="2 0 0" sleep="init">
            <geom type="box" size=".2 .2 .2"/>
            <joint type="ball" stiffness="300" damping="30"/>
            <body pos=".2 0 0">
              <geom type="cylinder" size="0.1" fromto="0 0 0 0 0 1"/>
              <joint type="slide" axis="0 0 1" springref="0.2" stiffness="1000" damping="100"/>
            </body>
          </body>
        </replicate>
      </replicate>
    </replicate>
  </worldbody>
</mujoco>