bullet3/data/sphere2.urdf

<?xml version="0.0" ?>
<robot name="urdf_robot">
  <link name="baseLink">
    <inertial>
      <origin rpy="0 0 0" xyz="0 0 0"/>
       <mass value="10.0"/>
       <inertia ixx="1" ixy="0" ixz="0" iyy="1" iyz="0" izz="1"/>
    </inertial>
    <visual>
      <origin rpy="0 0 0" xyz="0 0 0"/>
      <geometry>
      <sphere radius="0.5"/>
      </geometry>
    </visual>
    <collision>
      <origin rpy="0 0 0" xyz="0 0 0"/>
      <geometry>
	 <sphere radius="0.5"/>
      </geometry>
    </collision>
  </link>
   <link name="childA">
    <inertial>
      <origin rpy="0 0 0" xyz="0 0 0"/>
      <mass value="10.0"/>
      <inertia ixx="1" ixy="0" ixz="0" iyy="1" iyz="0" izz="1"/>
    </inertial>
    <visual>
      <origin rpy="0 0 0" xyz="0 0 0"/>
      <geometry>
        <sphere radius="0.5"/>
      </geometry>
    </visual>
    <collision>
      <origin rpy="0 0 0" xyz="0 0 0"/>
      <geometry>
        <sphere radius="0.5"/>
      </geometry>
    </collision>
  </link>
   <joint name="joint_baseLink_childA" type="fixed">
    <parent link="baseLink"/>
    <child link="childA"/>
    <origin xyz="0 0 1.0"/>
  </joint>
 <link name="childB">
    <inertial>
      <origin rpy="0 0 0" xyz="0 0 0.5"/>
      <mass value="10.0"/>
      <inertia ixx="1" ixy="0" ixz="0" iyy="1" iyz="0" izz="1"/>
    </inertial>
    <visual>
      <origin rpy="0 0 0" xyz="0 0 0.5"/>
      <geometry>
        <sphere radius="0.5"/>
      </geometry>
    </visual>
    <collision>
      <origin rpy="0 0 0" xyz="0 0 0.5"/>
      <geometry>
        <sphere radius="0.5"/>
      </geometry>
    </collision>
  </link>
 <joint name="joint_childA_childB" type="continuous">
    <parent link="childA"/>
    <child link="childB"/>
<axis xyz="0 1 0"/>
    <origin xyz="0 0 0.5"/>
  </joint>

</robot>