My robot us able to be controlled in gazebo, using the rosrun teleoptwist keyboard (node). However, if i directly use

rostopic pub /head_controller_1/command std_msgs/Float64 "data: 1000.0" 

or

rostopic pub /head_controller_/command std_msgs/Float64 "data: 1000.0" 

The robot is not moving in gazebo. But I can see the joints and the robot wheels rotating in Gazebo.

This is the code for my robots xacro file: I defined the controllers in a separate config.yaml file:

<?xml version="1.0" ?>

<robot name="walle" xmlns:xacro="http://www.ros.org/wiki/xacro">

<gazebo reference="base_link">
    <material>Gazebo/Blue</material>
</gazebo>
<gazebo reference="link_01">
    <material>Gazebo/Yellow</material>
</gazebo>
<gazebo reference="link_02">
    <material>Gazebo/Yellow</material>
</gazebo>

  <gazebo>
    <plugin filename="libgazebo_ros_diff_drive.so" name="differential_drive_controller">
      <legacyMode>false</legacyMode>
      <alwaysOn>true</alwaysOn>
      <updateRate>20</updateRate>
      <leftJoint>base_link__link_01</leftJoint>
      <rightJoint>base_link__link_02</rightJoint>
      <wheelSeparation>0.2</wheelSeparation>
      <wheelDiameter>0.35</wheelDiameter>
      <torque>0.1</torque>
      <commandTopic>cmd_vel</commandTopic>
      <odometryTopic>odom</odometryTopic>
      <odometryFrame>odom</odometryFrame>
      <robotBaseFrame>base_link</robotBaseFrame>
    </plugin>
  </gazebo>

    <link name="base_link">
        <visual>
            <origin rpy="0 0 0" xyz="0 0 0.1"/>
            <geometry>
                <box size="2 1 0.3"/>
            </geometry>
        </visual>

        <collision>
            <origin rpy="0 0 0" xyz="0 0 0.1"/>
            <geometry>
                <box size="2 1 0.3"/>
            </geometry>
        </collision>

        <inertial>
            <origin rpy="0 0 0" xyz="0 0 0.1"/>
            <mass value="1"/>
            <inertia ixx="0.03" ixy="0.0" ixz="0.0" iyy="0.03" iyz="0.0" izz="0.03"/>
        </inertial>

        <collision name="caster_front_collision">
            <origin rpy="0 0 0" xyz= "0.5 0 -0.05"/>
            <geometry>
                <sphere radius="0.25"/>
            </geometry>
            <surface>
                <friction>
                    <ode>
                        <mu>0</mu>
                        <mu2>0</mu2>
                        <slip1>1.0</slip1>
                        <slip2>1.0</slip2>
                    </ode>
                </friction>
            </surface>
        </collision>
        <visual name="caster_front_visual">
            <origin rpy="0 0 0" xyz ="0.5 0 -0.05"/>
                <geometry>
                    <sphere radius="0.25"/>
                </geometry>
        </visual>

    </link>

    <joint name="base_link__link_01" type="continuous">
        <axis xyz="0 1 0"/>
         <limit effort = "10.0" velocity="1.0"/>
         <joint_properties damping="1.0" friction="1.0"/>
        <!--<limit effort = "1000.0" lower="-3.14" upper="3.14" velocity="0.5"/>-->
        <origin rpy="0 0 0" xyz="-0.5 0.5 0"/>
        <parent link="base_link"/>
        <child link="link_01"/>
    </joint>

    <transmission name="trans_base_link__link_01">
        <type>transmission_interface/SimpleTransmission</type>
        <joint name="base_link__link_01">
            <hardwareInterface>hardware_interface/PositionJointInterface</hardwareInterface>
        </joint>
        <actuator name="motor_base_link__link_01">
            <hardwareInterface>hardware_interface/PositionJointInterface</hardwareInterface>
            <mechanicalReduction>1</mechanicalReduction>
        </actuator>
    </transmission>

    <link name="link_01">
        <visual>
            <origin rpy="0 1.5707 1.5707" xyz="0 0.2 0"/>
            <geometry>
                <cylinder radius="0.35" length="0.4"/>
            </geometry>
        </visual>

        <collision>
            <origin rpy="0 1.5707 1.5707" xyz="0 0.2 0"/>
            <geometry>
                <cylinder radius="0.35" length="0.4"/>
            </geometry>
        </collision>

        <inertial>
           <origin rpy="0 1.5707 1.5707" xyz="0 0.2 0"/>
            <mass value="1"/>
            <inertia ixx="0.03" ixy="0.0" ixz="0.0" iyy="0.03" iyz="0.0" izz="0.03"/>
        </inertial>     
    </link>


    <!--Second Wheel-->
    <joint name="base_link__link_02" type="continuous">
        <axis xyz="0 1 0"/>
         <limit effort = "10.0" velocity="1.0"/>
         <joint_properties damping="1.0" friction="1.0"/>
        <origin rpy="0 0 0" xyz="-0.5 -0.5 0"/>
        <parent link="base_link"/>
        <child link="link_02"/>
    </joint>

    <transmission name="trans_base_link__link_02">
        <type>transmission_interface/SimpleTransmission</type>
        <joint name="base_link__link_02">
            <hardwareInterface>hardware_interface/PositionJointInterface</hardwareInterface>
        </joint>
        <actuator name="motor_base_link__link_02">
            <hardwareInterface>hardware_interface/PositionJointInterface</hardwareInterface>
            <mechanicalReduction>1</mechanicalReduction>
        </actuator>
    </transmission>


    <link name="link_02">
        <visual>
            <origin rpy="0 1.5707 1.5707" xyz="0 -0.2 0"/>
            <geometry>
                <cylinder radius="0.35" length="0.4"/>
            </geometry>
        </visual>

        <collision>
            <origin rpy="0 1.5707 1.5707" xyz="0 -0.2 0"/>
            <geometry>
                <cylinder radius="0.35" length="0.4"/>
            </geometry>
        </collision>

        <inertial>
           <origin rpy="0 1.5707 1.5707" xyz="0 -0.2 0"/>
            <mass value="1"/>
            <inertia ixx="0.03" ixy="0.0" ixz="0.0" iyy="0.03" iyz="0.0" izz="0.03"/>
        </inertial>     
    </link>


        <!-- Add ROS plugin so we can interact with our robot -->
    <gazebo>
        <plugin name="gazebo_ros_control" filename="libgazebo_ros_control.so">
        </plugin>
    </gazebo>

</robot>