Robot Simulator in ROS

This is a simple robot simulator in ROS, which should avoid collision with the borders. It was done as a part of Research Track I course and written in C++.

Installing

The simulator required a World map, which was provided by professor Carmine Recchiuto in the following repository. Besides that, user should type catkin_make being in catkin workspace.

Exercise

To run script in the simulator, use roscore or roscore& (to run it in background) in your terminal at first. After that, you should run files from downloaded repository:

$ rosrun stage_ros stageros $(rospack find second_assignment)/world/my_world.world
$ rosrun second_assignment regulator
$ rosrun second_assignment controller

Note that second_assignment above should be changed on your folder name, where all of downloaded files from this repository are stored on your computer. For example catkin_ws/src/second_assignment/src/controller.cpp, where second_assignment is the name of your folder in your catkin workspace.

Task objectives

Requirements

• We can use ROS for controlling the robot
• The robot is endowed with laser scanners
• We want to have a node for the control of the robot, and an additional node which interacts with the user to: increase/decrease the speed and reset the robot’s position
• Everything should be done in cpp

Controlling the robot

• You should publish a velocity on the cmd_vel topic
• You can use the /base_scan topic to get information about the surrounding environment.
• In particular, the information about the distance of the obstacles is in the ranges vector.

Hint: divide the ranges vector into subsections, and take the minimum value of each subsection. This will provide information about the closest obstacles.

Additional specifications

• The node controlling the robot should also implement the functionality for increasing/decreasing the speed
• The UI node should constantly wait for an input for the user, which can either ask to increment or decrement the velocity, or to put the robot in the initial position.
• The robot may crash if the speed is increased too much.

Working principle of proposed solution

The proposed solution is simple and efficient and works almost perfectly. The solution consists of several cases when the robot needs to complete a particular command.

Control window

• UP arrow key = move on 0.25 faster.
• DOWN arrow key = move on 0.25 slower.
• R or r buttons = place robot on initial position.
• Q or q buttons = close program.
• Other buttons are not recognizible

Controller file

• We update our speed each time, meaning that our new_speed is equal to old_speed + 0.25. Besides that, we compare our new_speed with old_speed each time, in order to prevent it from going in reverse direction. For example if new_speed is negative, then it should stop, meaning that new_speed is equal to zero.
• Controller files calculates distance in 3 directions: in front of him, in right and left in order to calculate collision risk. Since robot has vision of 360 degress following restrictions was introduced. Front side is angle between 45 and 135, Leftside is angle between0 and 45andRightside is angle between135 and 180`.
• Taking into account above restrictions, if robot is too close to the borders threshold = 0.7 and osbtacle is from the left, then it should turn to right direction. Similarly, if obstacle is from the right side, then it should turn to left.

Regulator file

• This file is responbile for input commands. It uses ncurses.h, which allows to use arrow keys without waiting of pressing Enter from the user. Right after user presses Up arrow key or Down arrow key, robot will react and move with appropriate speed. The same thing is with Q - quit and R - reset.
• It publishes results of successful commands. If robot increases/decreases a speed, then it publishes it in the terminal.

Flowchart

Possible improvements

• In case if you will give to much acceleration to the robot and press Reset after that, acceleration will remain the same. For the future improvement, it will be better to reset acceleration as well, so robot will be placed at initial position with zero velocity and acceleration.
• Pause feature can be implemeneted as well in case user wants to pause the process.