Revision history [back]

• It's moving because the masses were set way too high. The inertial tensors correspond to something around 50 kg of mass, and the "mass" was set to 5 tons for the base and 0.5 tons for the wheels. Reduced that. I found Wikipedia's list of inertia tensors quite helpful.
• The visual and collision model of base_link did not match (that's why the robot appeared to be "floating").
• The wheels had no collision model (that's why they didn't show up).
• Transmissions for front wheels were commented out (that's why there were no joint_states published for them).

Also, there were some minor problems:

• use_sim_time has to be set to "true". Fixed in launch file.
• Don't run the joint_state_publisher while gazebo is running. Both publish joint_states and will interfere. Removed it from launch file.
• karlik.xacro: The <joint> element shouldn't have a sub-element <joint_properties>. AFAIK, it's not defined anywhere and confuses things like the joint_state_publisher. Deleted those lines.

You can get the fixed version here.