CSE 468 - Lab 1 - Solved

 Robotics Algorithms                                                                                              1

Robot Control and Using tf in ROS
The objective of this assignment is to get started with robot simulation in ROS, and use tf to relate the coordinate system of one robot with the other.

Before you get started, please make sure you have done the following:

• Complete ROS tutorials 1 through 12 (in Section 1.1 Beginner) and be able to write a simple publisher and subscriber in ROS

Simulation Setup
In this section, you will learn about launch files. Create a package named lab1 that depends on std msgs rospy roscpp. Download the world and launch files for this assignment from here. It contains three files - playground.world and playground.pgm which together form the initial stage world, and lab1.launch that is the initial launch file.

Please read the roslaunch tutorial to understand the roslaunch file. Drop the world files and the launch files in the appropriate sub-directories in the new package. Test to see if you can launch stage using the launch file by running the command $ roslaunch lab1 lab1.launch

Note:

•     You might need to re-run the path commands after creating the package for roslaunch to identify the new package lab1.

•     You don’t need to run roscore when you use roslaunch. However, you do need to have roscore running when you use rosrun

Evader Controller
In this section, you will write your own controller. Familiarize yourself with the given robot by checking the information it publishes and subscribes. The robot also has a laser range finder attached to it. Move the robot by dragging it with your mouse pointer to face a wall. Monitor the output of the laser by using rostopic echo in the command line. You should be able to understand the output of the sensor from the stage world file and its output you observed.
                                                                                             
Write a controller node that drives the robot straight at a constant speed of 2m/s. When the robot is close to an obstacle, the robot should stop, turn in a random new direction, and drive at the same speed. Create a new launch file evader.launch that adds the execution of this node to what was in the earlier launch file.

Pursuer-Evader
Read through the tf tutorial. Publish the coordinate frame of the robot wrt the global frame. Create a new world file with a second robot called pursuer, and drop it into the world close to the first robot. Write a controller node for the pursuer that subscribes to the tf messages from the evader, and follows the evader by going to the spot it was at from one second before. Create a third launch file pursuer-evader.launch to run the new world with the two robots, the evader controller, and the pursuer controller as separate nodes.