Used the namespace ana and the base_footprint frame for the skid steer gazebo plugin.

config/ana_sim_config.yaml

 rate: 100.0
-namespace: '/'
+namespace: '/ana'
 front_left_axle_joint: base_link_to_front_left_axle_joint
 front_right_axle_joint: base_link_to_front_right_axle_joint
 rear_left_axle_joint: base_link_to_rear_left_axle_joint
 rear_right_axle_joint: base_link_to_rear_right_axle_joint 
 wheel_separation: 0.4
 wheel_diameter: 0.215
-robot_base_frame: 'base_link'
+robot_base_frame: 'base_footprint'
 torque: 20
 cov_x: 0.0001
 cov_y: 0.0001