Obstacle Avoidance with TurtleBot and VFH

This example shows how to use a TurtleBot® with Vector Field Histograms (VFH) to perform obstacle avoidance when driving a robot in an environment. The robot wanders by driving forward until obstacles get in the way. The controllerVFH object computes steering directions to avoid objects while trying to drive forward.

Optional: If you do not already have a TurtleBot (simulated or real) set up, install a virtual machine with the Gazebo simulator and TurtleBot package. See to install and set up a TurtleBot in Gazebo.

Connect to the TurtleBot using the IP address obtained from setup.

rosinit('192.168.203.129',11311)
Initializing global node /matlab_global_node_18514 with NodeURI http://192.168.203.1:56701/

Create a publisher and subscriber to share information with the VFH class. The subscriber receives the laser scan data from the robot. The publisher sends velocity commands to the robot.

The topics used are for the simulated TurtleBot. Adjust the topic names for your specific robot.

laserSub = rossubscriber('/scan');
[velPub, velMsg] = rospublisher('/mobile_base/commands/velocity');

Set up VFH object for obstacle avoidance. Set the UseLidarScan property to true. Specify algorithm properties for robot specifications. Set target direction to 0 in order to drive straight.

vfh = controllerVFH;
vfh.UseLidarScan = true;
vfh.DistanceLimits = [0.05 1];
vfh.RobotRadius = 0.1;
vfh.MinTurningRadius = 0.2;
vfh.SafetyDistance = 0.1;

targetDir = 0;

Set up a Rate object using rateControl, which can track the timing of your loop. This object can be used to control the rate the loop operates as well.

rate = rateControl(10);

Create a loop that collects data, calculates steering direction, and drives the robot. Set a loop time of 30 seconds.

Use the ROS subscriber to collect laser scan data. Create a lidarScan object by specifying the ranges and angles. Calculate the steering direction with the VFH object based on the input laser scan data. Convert the steering direction to a desired linear and an angular velocity. If a steering direction is not found, the robot stops and searches by rotating in place.

Drive the robot by sending a message containing the angular velocity and the desired linear velocity using the ROS publisher.

while rate.TotalElapsedTime < 30

	% Get laser scan data
	laserScan = receive(laserSub);
	ranges = double(laserScan.Ranges);
	angles = double(laserScan.readScanAngles);
 
	% Create a lidarScan object from the ranges and angles
        scan = lidarScan(ranges,angles);
        
	% Call VFH object to computer steering direction
	steerDir = vfh(scan, targetDir);  
    
	% Calculate velocities
	if ~isnan(steerDir) % If steering direction is valid
		desiredV = 0.2;
		w = exampleHelperComputeAngularVelocity(steerDir, 1);
	else % Stop and search for valid direction
		desiredV = 0.0;
		w = 0.5;
	end

	% Assign and send velocity commands
	velMsg.Linear.X = desiredV;
	velMsg.Angular.Z = w;
	velPub.send(velMsg);
end

This code shows how you can use the Navigation Toolbox™ algorithms to control robots and react to dynamic changes in their environment. Currently the loop ends after 30 seconds, but other conditions can be set to exit the loop based on information on the ROS network (i.e. robot position or number of laser scan messages).

Disconnect from the ROS network

rosshutdown
Shutting down global node /matlab_global_node_18514 with NodeURI http://192.168.203.1:56701/