simulating.md

#Simulating in Gazebo

After the file has been loaded in the gazebo, now we will configure ROS and Gazebo for our model to be controlled through ROS.

Install Few softwares for ROS Control, by running this in terminal

sudo apt install ros-kinetic-ros-control ros-kinetic-ros-controllers  ros-kinetic-gazebo-ros ros-kinetic-gazebo-ros-control  ros-kinetic-gazebo-ros-pkgs

Step 1

Add wheel Transmission

To drive the robot around, we specify a transmission tag for each of the wheels from within the wheel macro.

You need to add the following just before closing of the wheel macro in the robot.xacro file

...
<gazebo reference="base_link_${name}_wheel">
  <mu1 value="200.0"/>
  <mu2 value="100.0"/>
  <kp value="10000000.0" />
  <kd value="1.0" />
  <material>Gazebo/Grey</material>
</gazebo>

<transmission name="base_link_${name}_wheel_trans">
  <type>transmission_interface/SimpleTransmission</type>
  <actuator name="base_link_${name}_wheel_motor">
    <mechanicalReduction>1</mechanicalReduction>
  </actuator>
  <joint name="base_link_${name}">
    <hardwareInterface>hardware_interface/VelocityJointInterface</hardwareInterface>
  </joint>
</transmission>
...

Step 2

Add Joint state Publisher from Gazebo

Create a file mobile_robot_simulation/config/joints.yaml with the contents

type: "joint_state_controller/JointStateController"
publish_rate: 50

Create a file mobile_robot_simulation/launch/state_publisher.launch with the contents

<?xml version="1.0"?>
<launch>
  <node pkg="robot_state_publisher" type="robot_state_publisher" name="robot_pub">
    <param name="publish_frequency" type="double" value="30.0" />
  </node>
</launch>

Now Update gazebo.launch file in mobile_robot_simulation package, adding the following after all the arg tags,

...
<rosparam command="load" file="$(find mobile_robot_simulation)/config/joints.yaml" ns="mobile_robot_joint_state_controller"/>

<node name="mobile_robot_controller_spawner" pkg="controller_manager" type="spawner" args="mobile_robot_joint_state_controller --shutdown-timeout 3"/>
...

Finally Update robot.launch file in mobile_robot package

Remove the state_publisher node from the file by REMOVING

...
<include file="$(find mobile_robot_description)/launch/state_publisher.launch">
  <arg name="use_gui" value="$(arg gui)"/>
</include>
....

And then replacing,

...
<group if="$(arg sim)">
  <include file="$(find mobile_robot_simulation)/launch/gazebo.launch"/>
</group>
...

WITH

...
<group unless="$(arg sim)">
  <include file="$(find mobile_robot_description)/launch/state_publisher.launch">
    <arg name="use_gui" value="$(arg gui)"/>
  </include>
</group>
<group if="$(arg sim)">
  <include file="$(find mobile_robot_simulation)/launch/state_publisher.launch"/>
  <include file="$(find mobile_robot_simulation)/launch/gazebo.launch"/>
</group>
...

Step 3

Adding Differential Drive

Create a file mobile_robot_simulation/config/diffdrive.yaml, and put the following

type: "diff_drive_controller/DiffDriveController"
publish_rate: 50

left_wheel: ['base_link_wh_left_back', 'base_link_wh_left_front']
right_wheel: ['base_link_wh_right_back', 'base_link_wh_right_front']

wheel_separation: 0.44

# Odometry covariances for the encoder output of the robot. These values should
# be tuned to your robot's sample odometry data, but these values are a good place
# to start
pose_covariance_diagonal: [0.001, 0.001, 0.001, 0.001, 0.001, 0.03]
twist_covariance_diagonal: [0.001, 0.001, 0.001, 0.001, 0.001, 0.03]

# Top level frame (link) of the robot description
base_frame_id: base_link

# Velocity and acceleration limits for the robot
linear:
  x:
    has_velocity_limits    : true
    max_velocity           : 0.2   # m/s
    has_acceleration_limits: true
    max_acceleration       : 0.6   # m/s^2
angular:
  z:
    has_velocity_limits    : true
    max_velocity           : 2.0   # rad/s
    has_acceleration_limits: true
    max_acceleration       : 6.0   # rad/s^2

Then add another rosparam in gazebo.launch file as follows,

...
<rosparam command="load" file="$(find mobile_robot_simulation)/config/diffdrive.yaml" ns="mobile_robot_diff_drive_controller"/>
...

And then update the controller in the same file from

<node name="mobile_robot_controller_spawner" pkg="controller_manager" type="spawner"
  args="mobile_robot_joint_state_controller --shutdown-timeout 3"/>

To

<node name="mobile_robot_controller_spawner" pkg="controller_manager" type="spawner"
  args="mobile_robot_joint_state_controller mobile_robot_diff_drive_controller --shutdown-timeout 3"/>

Step 4

Running in a terminal

roslaunch mobile_robot robot.launch

You should change the Fixed Frame from base_link to odom in RViz on the Left side pane, and Save the config.

Step 5

Running GUI

For this we need a package not installed by default in ROS,

So will install the ROS package like any other ROS package install, by running,

sudo apt install ros-kinetic-rqt-robot-steering

Now in a terminal run the node we just installed

rosrun rqt_robot_steering rqt_robot_steering

Now set the topic to publisher

/mobile_robot_diff_drive_controller/cmd_vel

Extras

You can check connections between all the running nodes by running this in terminal

rqt_graph

Also you can check the flow of transformation by running this,

rosrun rqt_tf_tree rqt_tf_tree