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mighty-controller

Second assignment for Robotics course @ USI 19/20. An open loop controller that moves a Thymio in Gazebo.

Contributors

Giorgia Adorni - giorgia.adorni@usi.ch GiorgiaAuroraAdorni

Elia Cereda - elia.cereda@usi.ch EliaCereda

Prerequisites

  • Python 2
  • ROS
  • Gazebo

Installation

Clone the repository

$ cd ~/catkin_ws/src
$ git clone https://github.com/GiorgiaAuroraAdorni/mighty-controller

Build the ROS packages and update the environment

$ catkin build
$ re.

Usage

Tasks

  1. The file task1_controller.launch is a launch file that contains the instruction to configure the node task1_controller.py, that implements an open loop controller to move the MyT along an "8" trajectory.

    The execution of Gazebo with one simulated Thymio can be started by running:

    $ roslaunch thymio_course_skeleton thymio_gazebo_bringup.launch name:=thymio10 world:=empty

    In order to see the Thymio moving in Gazebo run the command:

    $ roslaunch mighty-controller task1_controller.launch

    The execution of this task can be stopped by terminating the controller with Ctrl + C. A demonstration of the robot behavior can be found at the following link: task 1.

    Being an open-loop controller, we can see the robot correctly drawing an eight figure but gradually drifting away from the origin. This is already visible after one iteration and tends to get worse with time.

  2. The file task2_controller.launch is a launch file that contains the instruction to configure the node task2_controller.py, that moves the MyT straight ahead until it detects a wall without hitting it, using proximity sensors. Then turns the robot in place in such a way that the robot's x axis is orthogonal to the wall.
    Open Gazebo using the world 'wall':

    $ roslaunch thymio_course_skeleton thymio_gazebo_bringup.launch name:=thymio10 world:=wall

    To execute the task, run the command:

    $ roslaunch mighty-controller task2_controller.launch

    The execution of this task can be stopped by terminating the controller with Ctrl + C.

    We saw that the robot takes quite a bit of time to stop, so in the end we decided to stop the robot as soon as we detect an obstacle on the proximity sensors. This prevents the robot from bumping into the wall.

  3. The file compulsory.launch is a launch file that contains the instruction to configure the node task3_controller.py, that move the MyT straight ahead until it is close to an obstacle without hitting it, using the proximity sensors. Then turns the robot in such a way that it is facing opposite to the wall, then move and stop in such a way that its reference frame is as close as possible to a point that is 2 meters from the wall, in this case relying on odometry.
    In order to execute the final task, open Gazebo using the world 'wall':

    $ roslaunch thymio_course_skeleton thymio_gazebo_bringup.launch name:=thymio10 world:=wall

    Then, run the command:

    $ roslaunch mighty-controller compulsory.launch

    The execution of this task can be stopped by terminating the controller with Ctrl + C. A demonstration of the robot behavior can be found at the following link: compulsory task.

Bonus Tasks

  1. The file task4_controller.launch is a launch file that contains the instructions to configure the node task4_controller.py, that makes the MyT randomly explores an environment, avoiding any obstacles. In particular, it moves the MyT straight ahead until it is close to an obstacle, turning it in place (in a random direction) until it clears the obstacle and continuing to move straight.

    Deploy the robot in the arena world (it may take a few minutes for gazebo to load the world):

    $ roslaunch thymio_course_skeleton thymio_gazebo_bringup.launch name:=thymio10 world:=arena

    In order to see the Thymio moving in Gazebo run the command:

    $ roslaunch mighty-controller task4_controller.launch

    The execution of this task can be stopped by terminating the controller with Ctrl + C.

    One problem that we saw executing this task is that sometimes, when turning, the robot gets so close to a wall that the proximity sensors seemingly pass through to the other side and don't detect the obstacle anymore (for instance, in this video).

  2. The file bonus.launch is a launch file that contains the instruction to launch the same node of the previous task: it executes the task4_controller.py, but this time simulating two or more robots at once.

    Deploy the first robot in the arena world (it may take a few minutes for gazebo to load the world):

    $ roslaunch thymio_course_skeleton thymio_gazebo_bringup.launch name:=thymio10 world:=arena

    In order to spawn the second Thymio and start moving both in Gazebo, run the command:

    $ roslaunch mighty-controller bonus.launch

    The execution of this task can be stopped by terminating the controller with Ctrl + C. A demonstration of the robot behavior can be found at the following link: bonus task.

    The same weird behaviour we saw in task 4 is also present here.

    Adding a second robot on the other hand works well without any change to the code. In our experience, often one robot continues in its path without stopping, while the other stops and changes direction. When they both stop, if they randomly decide to turn in the same direction, they may meet again before being able to part ways but the probability this happens more than a few times decreases exponentially.

    The only drawback that we see in our controller is that it tends to follow the walls, so the middle of the room is explored less than the borders. On the other hand, this approach allows the robot to quickly move away from the obstacles and is robust even in case the robot gets stuck in a corner: it will just keep rotating in place until it's clear to go (in extreme cases, rotating 180º and going back from where it came).