Research Track I - First assignment

The purpose of the assignment is to control a robot in a 2D space, which is shown via a 2D simulator, and therefore comparable to a cartesian plane. In particular, the robot asks to the user for a random target to be reached. Any of these random targets have coordinates -6 and 6 both along x and y. Established the target, the robot goes to this one and then asks for a new random target.

Description of the package

The package is composed of two nodes:

• robot.cpp
• random_number.cpp

On top, the random_number.cpp has implemented a service Random.srv. This server accepts two floating points numbers as inputs and releases other two floating points numbers. The random_number.cpp node initializes the server and implements a function that returns a random number in a given interval. The server receives as input the interval and two numbers, that are the minimum and maximum acceptable number that the user can have as outputs. When a request is sent to the server, the random function is called twice passing as inputs the two numbers received from the server request, in order to generate the x and y coordinates that the robot will have to reach. The robot.cpp node initializes a client for the server random, a subscriber for the topic /odom and a publisher on the topic /cmd_vel. The subscriber on the topic /odom receives the position of the robot in a variable of type nav_msgs/Odometry. Everytime that the robot receives a new position, the function positionCallback is called and the values of the position and of the distances from the target are updated. The distance is calculated along x and y and it is computed using the distance formula for the coordinate plane. If the distance is less than 0.1, the robot.cpp node recall the server in order to ask for another target. As soon as a response is received from the server, the values of the target are updated. If the distance is not less than 0.1, a linear velocity is assigned along x and y both proportional to the distance along x and y respectively. That linear velocity is then published on the topic /cmd_vel.

How to launch

1. Open a shell, move to your catkin_ws and in the src folder type:

git clone https://github.com/RiccardoZuppetti/assignment1.git

2. Go to the root of your catkin_ws, and from there launch catkin_make

3. Start the ROS Master typing:

roscore &

3. Then launch the simulation environment through the command:

rosrun stage_ros stageros $(rospack find assignment1)/world/exercise.world

4. Open a second shell and type:

rosrun assignment1 random_number

5. Finally, open a third shell and type:

rosrun assignment1 robot