Differntial drive robot with wheel spin

Hi, created a differential drive robot with a ball caster. Tried to set mu1 and mu2 values of the wheels to values >1 and <1 for the caster. But the robot stands still and the wheels are slipping. Sometimes it moves slowly around the caster. You may find the xacro files here: [Robot definition](https://www.dropbox.com/sh/k0mro6vlnamvbrp/AAA28A8s9sUmx3ab2eH0SRnda?dl=0) Thanks for your help and any ideas. Marco Update: Added content of xacro files: hallrover_v2.xacro Gazebo/WhiteGazebo/WhiteGazebo/White hallrover_rollers_v2.xacro -------------------------- Gazebo/BlackGazebo/BlackGazebo/Black makros.xacro ------------ hallrover_v2.gazebo ------------------- /truefalse100.0body_to_roller_leftbody_to_roller_right${roller_body_space*2+hallrover_body_width}${roller_diam}20cmd_velodomodombase_footprint1.811 launch file - hallrover_v2_gazebo.launch ----------------------------------------