How to implement the Skid Steering Drive plugin in Gazebo and why do I not need transmission tags?

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Hello, I'm new to Gazebo and ROS and wanted to implement the skid steering plugin from Gazebo for the a very basic 4 wheeled 'robot' , but I'm not sure what how the axis are supposed to be set and what some of the requiried variables truly mean e.g torque (not sure which number I should give as input) or broadcastTF (not sure why I should not want to broadcast) . At the moment I can drive backwards and forwards but it the robot does not turn. Here is the xacro that I'm using at the moment:

<?xml version="1.0"?>
<robot xmlns:xacro="http://www.ros.org/wiki/xacro"   name="base1">
<!-- variables-->
<xacro:property name="length_wheel" value="0.1"/>
<xacro:property name="radius_wheel" value="0.2"/>
<xacro:property name="base_heigth" value="0.3"/>
<xacro:property name="base_width" value="0.6"/>
<xacro:property name="base_length" value="1.0"/>
<xacro:property name="hokuyo_box_size" value="0.05"/>
<xacro:property name="camera_box_size" value="0.05"/>
<!--<xacro::property name="offset" value=""/>-->
<xacro:property name="PI" value="3.14159265359"/>
<!-- Gazebo colors -->
<xacro:include filename="$(find own_base)/urdf/base1.gazebo"/>

<!-- macros-->
<xacro:macro name="default_inertial" params="mass">
<inertial>
    <mass value="${mass}"/>
    <inertia ixx="1.0" ixy="0.0" ixz="0.0" iyy="1.0" iyz="0.0" izz="1.0"/>
</inertial>
</xacro:macro>
<link name="base">
    <visual>
        <geometry>
            <box size="${base_length} ${base_width} ${base_heigth}"/>
        </geometry>
        <origin xyz="0 0 0" rpy="0 0 0"/>
        <material name="red">
            <color rgba="1 0 0 1"/>
        </material>       
    </visual>
    <collision>
        <geometry>
             <box size="${base_length} ${base_width} ${base_heigth}"/>
        </geometry>
        <origin xyz="0 0 0" rpy="0 0 0"/>
    </collision>
    <xacro:default_inertial mass="100"/>
</link>

   <link name="wheele_1">
        <visual>
         <geometry>
            <cylinder length="${length_wheel}" radius="${radius_wheel}"/>
        </geometry>
        <material name="black"> 
            <color rgba="0 0 0 1"/>
        </material>
        <origin xyz="0 0 0" rpy="0 0 0"/>

    </visual>
    <collision>
        <geometry>
            <cylinder length="${length_wheel}" radius="${radius_wheel}"/>
        </geometry>
        <origin xyz="0 0 0" rpy="0 0 0"/>
    </collision>
<xacro:default_inertial mass="5"/>
</link>

<link name="wheele_2">
        <visual>
         <geometry>
             <cylinder length="${length_wheel}" radius="${radius_wheel}"/>
        </geometry>
        <origin xyz="0 0 0" rpy="0 0 0"/>
        <material name="black"> 
            <color rgba="0 0 0 1"/>
        </material>
    </visual>
    <collision>
        <geometry>
            <cylinder length="${length_wheel}" radius="${radius_wheel}"/>
        </geometry>
        <origin xyz="0 0 0" rpy="0 0 0"/>
    </collision>
     <xacro:default_inertial mass="5"/>

</link>

<link name="wheele_3">
        <visual>
         <geometry>
             <cylinder length="${length_wheel}" radius="${radius_wheel}"/>
        </geometry>
        <origin xyz="0 0 0" rpy="0 0 0"/>
        <material name="black"> 
            <color rgba="0 0 0 1"/>
        </material>
    </visual>
    <collision>
        <geometry>
            <cylinder length="${length_wheel}" radius="${radius_wheel}"/>
        </geometry>
        <origin xyz="0 0 0" rpy="0 0 0"/>
    </collision>
     <xacro:default_inertial mass="5"/>
</link>


<link name="wheele_4">
        <visual>
         <geometry>
             <cylinder length="${length_wheel}" radius="${radius_wheel}"/>
        </geometry>
        <origin xyz="0 0 0" rpy="0 0 0"/>
        <material name="black"> 
            <color rgba="0 0 0 1"/>
        </material>
    </visual>
    <collision>
        <geometry>
            <cylinder length="${length_wheel}" radius="${radius_wheel}"/>
        </geometry>
        <origin xyz="0 0 0" rpy="0 0 0"/>
    </collision>
     <xacro:default_inertial mass="5"/>
</link>
<link name="hokuyo_link">
    <visual>
        <geometry>
            <box size="${hokuyo_box_size} ${hokuyo_box_size} ${hokuyo_box_size}"/>
        </geometry ...