ROS and MATLAB integration

"Moving turtlebot using MATLAB, ROS toolbox, and GAZEBO simulation"

For better look, please visit HackMD.io

by:
Liber Normous

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Requirements

1. MATLAB ROS Toolbox
   • Sometimes you need the latest MATLAB version to install ROS Toolbox.

Basic Step

For the robot

1. Set the MASTER IP address
   • example:
   ​​​​export ROS_MASTER_URI=http://192.168.50.101:11311
   

2. Set the robot IP address
   • example:
   ​​​​export ROS_IP=192.168.50.101
   

NOTE: In this case the robot is the MASTER. That is why the IP is the same

3. Start the ros core in the master node:
   • example:
   ​​​​roscore
   

NOTE: Most of the time roscore is included within roslaunch

For the MATLAB

1. Start communicating with MASTER

clc; clear;
rosshutdown;
rosinit('192.168.50.101');

NOTE: Use the master IP address. This will start MATLAB as a node

A class for MATLAB node

This is example for subscribing and publishing.

classdef robot < handle
    % `handle` is important so you can see values inside properties
    % `robot.m` is the name of the file
    % should match the file name

    properties(Access = public)
        odom_msg % storing the subscriber handle
        odom_sub % storing the message handle
        vel_pub % storing the publisher handle
        vel_msg % storing the message handle
    end
    
    methods(Access = public)
        function obj = robot()
            % CONSTRUCTOR
            % Codes in this function is run once at the begining
            % `robot.m` is the name of the file
            % name of constructor should match the file name

            %% pub init
            disp('publish init 2 s');
            obj.vel_pub = rospublisher('/cmd_vel','geometry_msgs/Twist');
            pause(2); % Wait to ensure publisher is registered
            obj.vel_msg = rosmessage(obj.vel_pub); % pub message

            %% sub init
            disp('subscribe init 4 s');
            obj.odom_msg = rosmessage('nav_msgs/Odometry');
            pause(2); % Wait to ensure subscriber is registered
            obj.odom_sub = rossubscriber('/odom',@obj.odom_cb);
            % obj.odom_cb is a callback function
            % it will run in parallel with the main program
            % function will be called everytime there is a new incoming message
 
            disp('init done');
        end
        
        function ret=get_odom_x_y_yaw(obj)
            R_x = obj.odom_msg.Pose.Pose.Position.X;
            R_y = obj.odom_msg.Pose.Pose.Position.Y;
            quat = [obj.odom_msg.Pose.Pose.Orientation.X ...
                obj.odom_msg.Pose.Pose.Orientation.Y ...
                obj.odom_msg.Pose.Pose.Orientation.Z ...
                obj.odom_msg.Pose.Pose.Orientation.W];
            rpy = quat2eul(quat);
            R_yaw = rpy(3);
            R_x_dot = obj.odom_msg.Twist.Twist.Linear.X;
            R_y_dot = obj.odom_msg.Twist.Twist.Linear.X;
            R_yaw_dot = obj.odom_msg.Twist.Twist.Angular.Z;
            ret = [R_x, R_y, R_yaw, R_x_dot, R_y_dot, R_yaw_dot];
        end

        function obj=pub_vel_cmd(obj, v_R, w_R)
            %publishing values to /cmd_vel
            obj.vel_msg.Linear.X = v_R;
            obj.vel_msg.Angular.Z = w_R;
            send(obj.vel_pub,obj.vel_msg);
            % send() is to publish the message
            % what we send is the message
            % using ROS message format
            % this case we send vel_msg
            % it has been formated accordingly
        end
    end
    
    methods(Access = private)
        function obj = odom_cb(obj,~, message)
            obj.odom_msg = message;
        end
    end
end

---

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Tutorial from MATLAB

Run turtlebot gazebo empty world simulation.

roslaunch turtlebot3_gazebo turtlebot3_world.launch

Then run this code section by section.

%% Clear 
clc; clear all;

%% start ROS master in MATLAB
% to connect outside ros master, use; rosinit('http://192.168.1.1:12000')
rosinit

%% RUn GAZEBO then List nodes
rosnode list

%%  Use rostopic list
rostopic list

%%  Use rostopic info <topicname> to get specific information about a specific topic
rostopic info /cmd_vel   

%% List service
rosservice list

%% service info
rosservice info /imu_service

%% shutdown ROS
% rosshutdown

%% subscribing
laser = rossubscriber('/scan');

%% try using data to visualize laser
angle = laser.LatestMessage.AngleMin:laser.LatestMessage.AngleIncrement:laser.LatestMessage.AngleMax;
x = laser.LatestMessage.Ranges.*cos(angle');
y = laser.LatestMessage.Ranges.*sin(angle');
plot(x, y, '.'); axis square;

%% asking/waiting data from subscribes topic
scandata = receive(laser,10);

figure(2)
plot(scandata,'MaximumRange',2) %mistery


%% subscribing using callback
laser = rossubscriber('/scan', @callback_func);

%% Create a publisher that sends ROS string messages to the /chatter topic (see Work with Basic ROS Messages).

chatterpub = rospublisher('/from_zee','std_msgs/String');
chattersub = rossubscriber('/from_zee', @callback_func);
pause(2); % Wait to ensure publisher is registered

%% Create and populate a ROS message to send to the /chatter topic.
chattermsg = rosmessage(chatterpub);
chattermsg.Data = 'hello world';
send(chatterpub,chattermsg);

%% Functions
function callback_func(~,callback_ret)
%exampleHelperROSEmptyCallback Callback function used by a ROS service server
%   exampleHelperROSEmptyCallback(~,~,RESP) returns no arguments. it simply
%   displays a message indicating that it has been called.
%
%   See also ROSServicesExample, exampleHelperROSCreateSampleNetwork.

%   Copyright 2014-2015 The MathWorks, Inc.

disp(callback_ret)
end

---

Moving the robot back and forth

This code will move the robot between 2 points. after reaching a point, the robot will turn into another point.
The point reference is /odom reading. That means the origin is the starting point.

This is the flow chart of the code.

This is the graph of the program.

Run turtlebot gazebo empty world simulation.

roslaunch turtlebot3_gazebo turtlebot3_world.launch

Then run this code.

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%%%Move back and fort using stupid controller%%%
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

%% Clear 
clc; clear all;

%% global variable
pose_sub_x = 0;
pose_sub_y = 0;
%% pub init
vel_pub = rospublisher('/cmd_vel','geometry_msgs/Twist');
pause(2); % Wait to ensure publisher is registered
vel_msg = rosmessage(vel_pub); % pub message

%% sub init
pose_sub = rossubscriber('/odom');
target_1 = [1 0];
target_2 = [0 0];
target=target_1;
pos_case = 1;

%% while loop
ts = 10;
while true
    pose_msg = receive(pose_sub,1);
    pose_sub_x = pose_msg.Pose.Pose.Position.X;
    pose_sub_y = pose_msg.Pose.Pose.Position.Y;
    quat = [pose_msg.Pose.Pose.Orientation.X ...
            pose_msg.Pose.Pose.Orientation.Y ...
            pose_msg.Pose.Pose.Orientation.Z ...
            pose_msg.Pose.Pose.Orientation.W];
    rpy = quat2eul(quat);
    yaw = rpy(3);
    
    x_d = target(1)-pose_sub_x;
    y_d = target(2)-pose_sub_y;
    
    ang = atan2(y_d, x_d);
    dist = sqrt(y_d^2 + x_d^2);
    
    disp([dist abs(ang - yaw)])
    
    if abs(ang - yaw) > (pi/10)
        vel_msg.Linear.X = 0;
        vel_msg.Angular.Z = 0.15*(2*pi)/ts; % 0.25 circle per 10 sec
        send(vel_pub,vel_msg); %send/pub the message
    else
        vel_msg.Linear.X = 1/ts;
        vel_msg.Angular.Z = 0;
        send(vel_pub,vel_msg); %send/pub the message
        if dist < 0.1 && pos_case == 1
            target = target_2;
            pos_case = 2;
        elseif dist < 0.1 && pos_case == 2
            target = target_1;
            pos_case = 1;
        else
            % nothing
        end
    end
end

Result:

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References

[1] Exchange Data with ROS Publishers and Subscribers
[2] quat2eul
[3] How to Move a Robot to a Certain Point Using Twist
[4]

tags: notes readme matlab robot