4 wheeled Robot does not Drive

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Hello,

I made a URDF-File for a 4-wheeled Robot. I would like to test it in Gazebo. I have it working so far. I have 4 wheels, they also turn. I confirmed this by turning on View -> Wireframe. I am using the skid_steer_drive_controller and rosrun teleop_twist_keyboard teleop_twist_keyboard.py. I can see the wheels turning but the Robot does not move.

I am using an offset for my base_footprint, otherwise my robot collapses and starts jiggeling. I also took this offset in the z-Axis in account for the wheels.

I took this urdf as basis, here so i did not declare friction:

https://github.com/noshluk2/ROS-Navig...

This is my URDF:

<?xml version="1.0" ?>
 <robot name="explorer">
  <link name="world">
  </link>
<!-- -->
  <link name="base_footprint">
    <visual>
      <origin xyz="0 0 0.046"/>
      <geometry>
          <box size="0.235 0.094 0.049"/>
      </geometry>
      <material name="gray">
        <color rgba=".2 .2 .2 1" />
      </material>
    </visual>
    <inertial>
      <origin xyz="0 0 0.046"/>
        <mass value="0.6174" />
          <inertia ixx="2.84523645e-3" ixy="0.0" ixz="0" iyy="3.1763172e-3" iyz="0" izz="5.7814365e-4" />
    </inertial>
      <collision>
        <origin xyz="0 0 0.046"/>
        <geometry>
          <box size="0.235 0.094 0.049"/>
        </geometry>
      </collision>
  </link>
  <joint name="dummy_joint" type="fixed">
    <parent link="world"/>
    <child link="base_footprint"/>
  </joint>

 <!-- -->
 <link name="wheel_rf">
  <inertial>
    <mass value="0.036" />
    <inertia ixx="9.2562e-5" ixy="0.0" ixz="0" iyy="9.2562e-5" iyz="0" izz="2.9124e-5" />
  </inertial>
  <visual>
    <geometry>
        <cylinder radius="0.033" length="0.026"/>
    </geometry>
    <material name="white">
      <color rgba="1 1 1 1"/>
    </material>
  </visual>
  <collision>
    <geometry>
        <cylinder radius="0.033" length="0.026"/>
    </geometry>
  </collision>
</link>
<joint name="wheel_rf_joint" type="continuous">
  <origin xyz="0.04 0.063 0.033" rpy="1.57  0.0 0.0"/>
  <parent link="base_footprint"/>
  <child link="wheel_rf"/>
     <axis xyz="0.0 0.0 1.0"/> 
</joint>

<link name="wheel_lf">
  <inertial>
    <mass value="0.036" />
    <inertia ixx="9.2562e-5" ixy="0.0" ixz="0" iyy="9.2562e-5" iyz="0" izz="2.9124e-5" />
  </inertial>
  <visual>
    <geometry>
        <cylinder radius="0.033" length="0.026"/>
    </geometry>
    <material name="white">
      <color rgba="1 1 1 1"/>
    </material>
  </visual>
  <collision>
    <geometry>
        <cylinder radius="0.033" length="0.026"/>
    </geometry>
     </collision>
</link>

<joint name="wheel_lf_joint" type="continuous">
  <origin xyz="0.04 -0.063 0.033" rpy="1.57 0.0 0.0"/>
  <parent link="base_footprint"/>
  <child link="wheel_lf"/>
     <axis xyz="0.0 0.0 1.0"/>

</joint>
<!-- -->
 <link name="wheel_rb">
  <inertial>
    <mass value="0.036" />
    <inertia ixx="9.2562e-5" ixy="0.0" ixz="0" iyy="9.2562e-5" iyz="0" izz="2.9124e-5 ...