How to control a rotating joint in velocity

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Hello everyone,

I'm trying to control a rotating joint type "continuous" in velocity, and simulate it in Gazebo.

This is the URDF joint definition:

<joint name="${name}_joint" type="continuous"> 
      <xacro:insert_block name="origin" />
      <parent link="${namespace}/${parent}"/>
      <child link="${namespace}/${name}"/>
      <axis xyz="1 0 0" rpy="0 0 0" />
      <limit effort="2000.0" velocity="40.0" />
    </joint>

    <gazebo>
      <plugin name="gazebo_ros_control" filename="libgazebo_ros_control.so">
        <robotNamespace>${namespace}</robotNamespace>
      </plugin>
    </gazebo>

    <transmission name="${name}_joint_trans">
      <type>transmission_interface/SimpleTransmission</type>
      <joint name="${name}_joint">
        <hardwareInterface>hardware_interface/VelocityJointInterface</hardwareInterface>
      </joint>
      <actuator name="${name}_joint_motor">
        <hardwareInterface>hardware_interface/VelocityJointInterface</hardwareInterface>
        <mechanicalReduction>1</mechanicalReduction>
      </actuator>
    </transmission>

and the config yaml file for controllers:

 joint_state_controller:
    type: joint_state_controller/JointStateController
    publish_rate: 60

  my_joint_position_controller:
    type: velocity_controllers/JointVelocityController
    joint: my_joint
    pid: {p: 0.5, i: 0.6, d: 0.0035}

I have couple of questions:

• first, can someone explain the yaml file or give a tutorial explaining this? what is "publish_rate" and what is its role? how can influence the rotation? same for "joint_state_controller"?

• Second, to change the joint velocity I run :

  rostopic pub /my_joint_position_controller/command std_msgs/Float64 "data: 5.0"

  the data value is a linear velocity (m/s) or rotational velocity (rad/s) ? If it is a linear velocity, how can I transform that to rotational velocity (rad/s)?

• third, how can I get the joint angle at every moment?

Thanks in advance.