The objective is to control a simulated robot within the stage environment. This will help us in writing our own control algorithms for controlling the simulated robot. Please follow the steps given below:
#1 Follow the instructions on this page. This package demonstrates how one can run a stage simulation through stageros. Basically tells you to download the package stage_controllers.tar.gz and compile and build the package within a folder where ROS can find it.
$ rosmake stage_controllers
$ rospack find stage_controllers
$ rosrun stage stageros `rospack find stage_controllers`/world/roomba-wander.world
You should be able to see a robot moving around in a stage environment as shown in the picture.
#2 Now we want to stop this robot moving and write a C++ program to provide the necessary motion command. In order to achieve this, open the file ‘/world/roomba-wander.world’ inside the stage_controllers folder and comment out the line that contains the word “wander” as shown below:
roomba
(
# can refer to the robot by this name
name "roomba"
pose [ -8 6 0 0 ]
sicklaser()
#ctrl "wander"
)
If you now execute the above commands you will see a stationary robot within the stage environment. Now we need to write a C++ program to get the robot moving again.
#3 Create a file ‘robctrl.cpp’ inside ‘stage_controllers/src/’ folder that contains the following piece of code:
#include "ros/ros.h"
#include "std_msgs/String.h"
#include "geometry_msgs/Twist.h"
#include
int main(int argc, char **argv)
{
ros::init(argc, argv, "RobCtrl");
ros::NodeHandle n;
ros::Publisher cmd_pub = n.advertise
geometry_msgs::Twist cmd_msg;
ros::Rate cycle(10.0);
//Specify the velocity
cmd_msg.linear.x = 0.1;
cmd_msg.linear.y = 0;
cmd_msg.linear.z = 0;
cmd_msg.angular.x = 0;
cmd_msg.angular.y = 0;
cmd_msg.angular.z = 0.2;
while(ros::ok())
{
cmd_pub.publish(cmd_msg);
cycle.sleep();
}
return 0;
}
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#4 Edit the stage_controllers/manifest.xml to reflect dependency on stage package.
#5 Add the following line to the end of the ‘CMakeLists.txt’ file
rosbuild_add_executable(stage_controllers src/robctrl.cpp)
#6 Build
$ rosmake stage_controllers stage_controllers
# Execute
$ roscore (on one window)
$ rosrun stage stageros `rospack find stage_controllers`/world/roomba-wander.world (on another window)
$ rosrun stage_controllers stage_controllers
You should see the robot rotating in a circle within the stage environment.
This program publishes the velocity values to the topic ‘/cmd_vel’. To know about the available topics where the data could be published, use ‘rostopic’ and ‘rxgraph’ command.
$ rostopic list -v
Published topics:
* /base_scan [sensor_msgs/LaserScan] 1 publisher
* /rosout [rosgraph_msgs/Log] 2 publishers
* /tf [tf/tfMessage] 1 publisher
* /clock [rosgraph_msgs/Clock] 1 publisher
* /odom [nav_msgs/Odometry] 1 publisher
* /rosout_agg [rosgraph_msgs/Log] 1 publisher
* /cmd_vel [geometry_msgs/Twist] 1 publisher
* /base_pose_ground_truth [nav_msgs/Odometry] 1 publisher
Subscribed topics:
* /clock [rosgraph_msgs/Clock] 2 subscribers
* /rosout [rosgraph_msgs/Log] 1 subscriber
* /cmd_vel [geometry_msgs/Twist] 1 subscriber
$ rxgraph
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