Gazebo does not show revolute joint but only fixed joint [closed]

edit

Hi all, I am new here and sorry I can not upload images. I tried to build a "robot". Here is my urdf file. <robot <a="" href="http://xmlns:xacro="http://www.ros.org/wiki/xacro%22" name="scarabot">xmlns:xacro="http://www.ros.org/wiki/...></robot>

<link name="linkbase"> <collision> <origin rpy="0 0 0" xyz="0 0 0"/> <geometry> <box size="1 1 0.2"/> </geometry> </collision>

<visual>
  <origin rpy="0 0 0" xyz="0 0 0"/>
  <geometry>
    <box size="1 1 0.2"/>
  </geometry>
</visual>

<inertial>
  <origin rpy="0 0 0" xyz="0 0 0"/>
  <mass value="10"/>
  <inertia ixx="0.0" ixy="0.0" ixz="0.0" iyy="0" iyz="0.0" izz="0.0"/>
</inertial>

</link>

<joint name="joint1" type="revolute"> <axis xyz="0 0 1"/> <limit effort="10" lower="0.0" upper="0.5" velocity="0.1"/> <origin rpy="0 0 0" xyz="0 0 0.1"/> <parent link="linkbase"/> <child link="link1"/> </joint>

<link name="link1"> <collision> <origin rpy="0 0 0" xyz="0 0 0.25"/> <geometry> <cylinder radius="0.15" length="0.5"/> </geometry> </collision>

<visual>
  <origin rpy="0 0 0" xyz="0 0 0.25"/>
  <geometry>
    <cylinder radius="0.15" length="0.5"/>
  </geometry>
</visual>

<inertial>
  <origin rpy="0 0 0" xyz="0 0 0"/>
  <mass value="1"/>
  <inertia ixx="0.0" ixy="0.0" ixz="0.0" iyy="0.0" iyz="0.0" izz="0.0"/>
</inertial>

</link>

<joint name="joint2" type="fixed"> <origin rpy="0 0 0" xyz="0 0 0.5"/> <parent link="link1"/> <child link="link2"/> </joint>

<link name="link2"> <collision> <origin rpy="0 0 0" xyz="0 0 0.3"/> <geometry> <box size="0.03 0.03 0.6"/> </geometry> </collision>

<visual>
  <origin rpy="0 0 0" xyz="0 0 0.3"/>
  <geometry>
    <box size="0.03 0.03 0.6"/>
  </geometry>
</visual>

<inertial>
  <origin rpy="0 0 0" xyz="0 0 0"/>
  <mass value="0"/>
  <inertia ixx="0.0" ixy="0.0" ixz="0.0" iyy="0.0" iyz="0.0" izz="0.0"/>
</inertial>

</link>

<joint name="joint3" type="fixed"> <origin rpy="0 0 0" xyz="0.015 0 0.585"/> <parent link="link2"/> <child link="link3"/> </joint>

<link name="link3"> <collision> <origin rpy="0 0 0" xyz="0.3 0 0"/> <geometry> <box size="0.6 0.03 0.03"/> </geometry> </collision>

<visual>
  <origin rpy="0 0 0" xyz="0.3 0 0"/>
  <geometry>
    <box size="0.6 0.03 0.03"/>
  </geometry>
</visual>

<inertial>
  <origin rpy="0 0 0" xyz="0 0 0"/>
  <mass value="0"/>
  <inertia ixx="0.0 ...