Lab 1

Slides available here.

The goal for this lab is to get you introduced with ROS.

For this lab we are going to work with stage simulator. The following instructions have been tested under Ubuntu 16.04 and ROS kinetic.

  1. Install ros stage

     sudo apt install ros-kinetic-stage-ros

  2. Ensure that you are able to go into the package:

     roscd stage
 roscd stage_ros

  3. Explore the stage package, take a look at the bitmaps. Stage will create worlds based on this 2d bitmaps.

     roscd stage/worlds/bitmaps/
 nautilus .

  4. Run stage (in 2 terminals!):

     roscore
 rosrun stage_ros stageros $(rospack find stage)/worlds/pioneer_walle.world

    NOTE: The following warning is normal: [WARN] [/stageros]: ROS Stage currently supports rangers with 1 sensor only.

    You should be able to see now 2 robots: 1 pioneer and 1 wall-e

  5. Play around with stage options:

    • press R -> perspective camera
    • mouse right click -> drag to change the camera position

  6. list the current topics:

     rostopic list

  7. move the robot (rotate):

     rostopic pub -r 10 /robot_0/cmd_vel geometry_msgs/Twist "{linear: {x: 0.0, y: 0.0, z: 0.0}, angular: {x: 0.0, y: 0.0, z: 0.1}}"

  8. move the robot (forward):

     rostopic pub -r 10 /robot_0/cmd_vel geometry_msgs/Twist "{linear: {x: 0.1, y: 0.0, z: 0.0}, angular: {x: 0.0, y: 0.0, z: 0.0}}"

  9. Analyze a bit the situation:

    • If you want more information about rostopic command, check the following website: http://wiki.ros.org/rostopic

    • Check at which rate is publishing the data:

        rostopic hz /robot_0/cmd_vel

    • Echo the data on another terminal:

        rostopic echo /robot_0/cmd_vel

  10. teleoperate the robot with the keyboard

    sudo apt-get install ros-kinetic-teleop-twist-keyboard
rosrun teleop_twist_keyboard teleop_twist_keyboard.py cmd_vel:=/robot_0/cmd_vel

    • move the robot by pressing the following keys on your keyboard:

        u    i    o
  j    k    l
  m    ,    .

  11. reset robot positions using service call:

    rosservice call /reset_positions "{}"

  12. Create a behavior for the pioneer robot so that moves forward until it has an obstacle at 1.0 m then stops and starts rotating to the right until the object is no longer so close. It should loop through this behaviour infinitely.

    • Use the pioneer_behavior.py file and complete the parts of the code that are missing.

    • Hint: follow the tutorial it will help you to understand how to publish / subscribe to topics in ros using python code

    • You can run the file by copying the content of the file pioneer_behavior.py to the node of the package you created in the first step and the run the corresponding executable using rosrun.

  13. in order to modify the wall threshold, for instance to 5.0m, you can do it via command line by setting the following parameter:

    rosparam set /distance_threshold 5.0

  14. Watch the following youtube video to get see an example of one posible solution for the problem in this lab.

  15. Check additional resources: