ROS Selection Task 2023-2024

Problem statement

The objective of the task is to move the turtle inside the turtlesim window in a vertical Z shape
To acheive this task you are supposed to create a node named /node_turtle_move within a python script, node_turtle_move.py

Dont worry if you are new to ROS or Linux(Ubuntu), the task is fairly simple and we have provided you with ample resource and tutorials in this WIKI to the complete this task so only a strong will and a little bit of brains is required to get the work done. Also even though this just a weekend task we have provided ample amount of time as we also have our midterm exams during this time. So we think a week time is enough so you guys can give your exams freely and manage your time in order to complete the task

Note

All the resources to complete the said task are provided in the ROS section of ATOM WIKI. So make sure to check it out if you are new to ROS.

Warning

The Deadline for completing the task: 16th October, 2023

Expected Output

Note

THE Z SHOULD BE VERTICAL .

Hints

The turtle needs to move in a vertical ‘Z’ shape .
You can refer POSE to learn more about pose function.
You can refer TWIST to learn more about twist function.
Use linear velocity and angular velocity to get this done.
Keep tracking the distance travelled so as to know when to stop. You can refer to Overview of rospy for more hint

Sample Code Snippet

Question: Write a python code to move ROS’s turtlesim bot on a straight path while bot’s distance is less than 6.

#! /usr/bin/env python3

import rospy
from geometry_msgs.msg import Twist
from turtlesim.msg import Pose

my_X = 0
my_Y = 0
x_dist = 6

# Subscriber Callback that gives position of the turtle (x & y)
def pose_callback(pose):

   global my_X, my_Y
   rospy.loginfo("Robot X = %f: Robot Y=%f\n",pose.x,pose.y)
   my_X = pose.x
   my_Y = pose.y

def move_turtle(lin_vel):

   global my_X
   rospy.init_node('move_turtle', anonymous=True)
   pub = rospy.Publisher('/turtle1/cmd_vel', Twist, queue_size=10)
   rospy.Subscriber('/turtle1/pose',Pose, pose_callback)

   rate = rospy.Rate(10) # 10hz
   vel = Twist()
   while not rospy.is_shutdown():

      vel.linear.x = lin_vel
      vel.linear.y = 0
      vel.linear.z = 0
      vel.angular.x = 0
      vel.angular.y = 0
      vel.angular.z = 0

      rospy.loginfo("Linear Vel = %f: ", lin_vel)

      # Stop the turtle when it reaches x_dist
      if(x_dist < my_X ):
         rospy.loginfo("Turtle Reached destination")
         rospy.logwarn("Stopping Turtle")

         break

      pub.publish(vel)
      rate.sleep()

move_turtle(2.0)

Output video

Commands used:

roscore
rosrun turtlesim turtlesim_node
rosrun package_name script_name

Procedure

Follow the instructions given below to get started with the task.

First, you will need to create a package named selection_task within your ROS workspace. Once your package is created, source and build your workspace.
Within this package, you should have a ‘scripts’ folder inside which you’ll create a python script, named node_turtle_move.py.
Fill the script with proper programming ethics. Doing this will help us understand your code better and quicker than usual.
After completing the python script. Make it executable, if it isn’t already. To do that, enter the following code.

cd ~/catkin_ws
catkin_make
source devel/setup.bash
chmod +x ~/catkin_ws/src/selection_task/scripts/node_turtle_move.py

Before executing make sure that roscore is running along with turtlesim_node. You can either run them in separate terminals or simply create a selection_task.launch file inside the ~/catkin_ws/src/selection_task/launch/ folder. Launch file can run multiple nodes unlike a python/cpp script. Run the launch file, enter, This should run three processes in parallel.
roscore
turtlesim_node
node_turtle_move.py