Added Videos in webm format

04_MobileRobot/README.md

@@ -83,7 +83,7 @@ Now we will **create a 2D map** of this world. We will later use this 2D map to
 - Now that you have familiarized yourself with the mapping process, let us now use a ROS code to do **autonomous mapping** where the robot will randomly move through the world and map it. Maybe you have to make the script *simple_auto_drive.py* as an executable by following instructions below.
 
     ```bash
-    roscd ~/catkin_ws/src/task_3/scripts
+    cd ~/catkin_ws/src/task_3/scripts
     ```
 
     ```bash
@@ -102,6 +102,12 @@ Now we will **create a 2D map** of this world. We will later use this 2D map to
     <source src="images/random-mapping.mp4" type="video/mp4">
 </video>
 
+- When the robot explored the environment and detected all obstacles you can save the created map. Use the following node to save your map. This map can be used later when navigating the robot.
+
+    ```bash
+    rosrun map_server map_saver -f ~/map
+    ```
+
 ## Task 4.1
 
 - Running the [simple_auto_drive.py](../00_GettingStarted/docker/i2r/catkin_ws/src/task_3/scripts/simple_auto_drive.py) code move the robot **in a random manner**. This will work if the area is wide open and you don't have any closed structures like rooms to explore.
@@ -136,6 +142,7 @@ If within a threshold:
 - We have provided an example output below. You can clearly see that **the robot doesn't always move parallel to the wall.** Sometimes it might even be far away from the wall. However, it still satisfies the task requirement that **it should not move between the white pillars**. Also, remeber that **we are not expecting you to reprodue the output shown in the example.** Just make sure that you staisfy the requirement of the task.
 
 <video width="640" height="480" controls>
+    <source src="images/mapping.webm" type="video/webm">
     <source src="images/mapping.mp4" type="video/mp4">
 </video>
 
@@ -151,11 +158,11 @@ Now that you have created a map of the world you can use this 2D map to localize
 - The following command will initialize the [amcl](http://wiki.ros.org/amcl) node which is used for localizing the robot inside a given map and [move_base](http://wiki.ros.org/move_base) node which is responsible for planning the path to a given goal location. These two packages are most widely used in research and for industrial purposes.
 
 ```bash
-roslaunch turtlebot3_navigation turtlebot3_navigation.launch
+roslaunch turtlebot3_navigation turtlebot3_navigation.launch map_file:=$HOME/map.yaml
+
 ```
 
-- Now you can use initialize the robot's pose on the map using the `2D Pose Estimate` tool that you will find on the top bar in the RVIZ window. You can also refer to a guide [here](Estimate Initial Pose
-) that will help you do this.
+- Now you can use initialize the robot's pose on the map using the `2D Pose Estimate` tool that you will find on the top bar in the RVIZ window. You can also refer to a guide [here](https://emanual.robotis.com/docs/en/platform/turtlebot3/navigation/#navigation) that will help you do this.
 
 - Once the robot's pose is initialized on the map you can use the `2D Nav Goal` tool to provide a navigation goal that the robot will reach.