Does "DefaultRobotHWSim" suppot DifferentialTransmission?

[dani-carbonell]

I am trying to model a robotic arm with 5 DoF and the last two joints are differential. That's why I use a DifferentialTransmission in its description.
I am using ROS Melodic and Ubuntu 18.04.
This is the robot i am trying to model:
https://github.com/dani-carbonell/rm501_robot/tree/master/rm501_description

The only robot I could find using DifferentialTransmissions is the Tiago wrist_transmission (@pal-robotics @v-lopez) and I guess its working fine in simulation. Also note that its robot type is using "pal_hardware_gazebo/PalHardwareGazebo" , witch inherits from "DefaultRobotHWSim " and runs the check for the number of Joints per Transmission in the Init Function:

...
PalHardwareGazebo::PalHardwareGazebo() : DefaultRobotHWSim()
{
}

bool PalHardwareGazebo::initSim(const std::string& robot_ns, ros::NodeHandle nh,
                                gazebo::physics::ModelPtr model,
                                const urdf::Model* const urdf_model,
                                std::vector<transmission_interface::TransmissionInfo> transmissions)
{
  ROS_INFO_STREAM("Loading PAL HARWARE GAZEBO");

  if (!DefaultRobotHWSim::initSim(robot_ns, nh, model, urdf_model, transmissions))
  {
    return false;
}
...

This is the error:

...
[ INFO] [1544538081.517258500]: Loading gazebo_ros_control plugin
[ INFO] [1544538081.517445708]: Starting gazebo_ros_control plugin in namespace: /rm501
[ INFO] [1544538081.518443693]: gazebo_ros_control plugin is waiting for model URDF in parameter [/robot_description] on the ROS param server.
[ WARN] [1544538081.673166191]: Transmission rm501_joint4_trans has more than one joint. Currently the default robot hardware simulation interface only supports one.
[ INFO] [1544538081.676993795]: Loaded gazebo_ros_control.
[urdf_spawner-4] process has finished cleanly
...

Thanks for the support.