[ad_1]
By Marco Arruda
On this put up you’ll discover ways to program a robotic to keep away from obstacles utilizing ROS2 and C++. As much as the top of the put up, the Dolly robotic strikes autonomously in a scene with many obstacles, simulated utilizing Gazebo 11.
You’ll be taught:
Tips on how to publish AND subscribe subjects in the identical ROS2 Node
Tips on how to keep away from obstacles
Tips on how to implement your individual algorithm in ROS2 and C++
1 – Setup atmosphere – Launch simulation
Earlier than anything, be sure you have the rosject from the earlier put up, you’ll be able to copy it from right here.
Launch the simulation in a single webshell and in a unique tab, checkout the subjects we’ve accessible. It’s essential to get one thing much like the picture beneath:
2 – Create the node
With a view to have our impediment avoidance algorithm, let’s create a brand new executable within the file ~/ros2_ws/src/my_package/obstacle_avoidance.cpp:
#embody “geometry_msgs/msg/twist.hpp” // Twist
#embody “rclcpp/rclcpp.hpp” // ROS Core Libraries
#embody “sensor_msgs/msg/laser_scan.hpp” // Laser Scan
utilizing std::placeholders::_1;
class ObstacleAvoidance : public rclcpp::Node {
public:
ObstacleAvoidance() : Node(“ObstacleAvoidance”) {
auto default_qos = rclcpp::QoS(rclcpp::SystemDefaultsQoS());
subscription_ = this->create_subscription(
“laser_scan”, default_qos,
std::bind(&ObstacleAvoidance::topic_callback, this, _1));
publisher_ =
this->create_publisher(“cmd_vel”, 10);
}
personal:
void topic_callback(const sensor_msgs::msg::LaserScan::SharedPtr _msg) {
// 200 readings, from proper to left, from -57 to 57 degress
// calculate new velocity cmd
float min = 10;
for (int i = 0; i < 200; i++) { float present = _msg->ranges[i];
if (present < min) { min = present; } }
auto message = this->calculateVelMsg(min);
publisher_->publish(message);
}
geometry_msgs::msg::Twist calculateVelMsg(float distance) {
auto msg = geometry_msgs::msg::Twist();
// logic
RCLCPP_INFO(this->get_logger(), “Distance is: ‘%f'”, distance);
if (distance < 1) {
// flip round
msg.linear.x = 0;
msg.angular.z = 0.3;
} else {
// go straight forward
msg.linear.x = 0.3;
msg.angular.z = 0;
}
return msg;
}
rclcpp::Writer::SharedPtr publisher_;
rclcpp::Subscription::SharedPtr subscription_;
};
int primary(int argc, char *argv[]) {
rclcpp::init(argc, argv);
rclcpp::spin(std::make_shared());
rclcpp::shutdown();
return 0;
}
In the principle operate we’ve:
Initialize node rclcpp::init
Maintain it operating rclcpp::spin
Inside the category constructor:
Subcribe to the laser scan messages: subscription_
Publish to the robotic diff driver: publisher_
The impediment avoidance intelligence goes inside the strategy calculateVelMsg. That is the place choices are made based mostly on the laser readings. Discover that’s relies upon purely on the minimal distance learn from the message.
If you wish to customise it, for instance, contemplate solely the readings in entrance of the robotic, and even test whether it is higher to show left or proper, that is the place you want to work on! Keep in mind to regulate the parameters, as a result of the best way it’s, solely the minimal worth involves this technique.
3 – Compile the node
This executable is determined by each geometry_msgs and sensor_msgs, that we’ve added within the two earlier posts of this sequence. Be sure to have them originally of the ~/ros2_ws/src/my_package/CMakeLists.txt file:
# discover dependencies
find_package(ament_cmake REQUIRED)
find_package(rclcpp REQUIRED)
find_package(geometry_msgs REQUIRED)
find_package(sensor_msgs REQUIRED)
And at last, add the executable and set up it:
# impediment avoidance
add_executable(obstacle_avoidance src/obstacle_avoidance.cpp)
ament_target_dependencies(obstacle_avoidance rclcpp sensor_msgs geometry_msgs)
…
set up(TARGETS
reading_laser
moving_robot
obstacle_avoidance
DESTINATION lib/${PROJECT_NAME}/
)
Compile the package deal:colcon construct –symlink-install –packages-select my_package
4 – Run the node
With a view to run, use the next command:ros2 run my_package obstacle_avoidance
It won’t work for this robotic! Why is that? We’re subscribing and publishing to generic subjects: cmd_vel and laser_scan.
We want a launch file to remap these subjects, let’s create one at ~/ros2_ws/src/my_package/launch/obstacle_avoidance.launch.py:
from launch import LaunchDescription
from launch_ros.actions import Node
def generate_launch_description():
obstacle_avoidance = Node(
package deal=”my_package”,
executable=”obstacle_avoidance”,
output=”display”,
remappings=[
(‘laser_scan’, ‘/dolly/laser_scan’),
(‘cmd_vel’, ‘/dolly/cmd_vel’),
]
)
return LaunchDescription([obstacle_avoidance])
Recompile the package deal, supply the workspace as soon as extra and launch it:colcon construct –symlink-install –packages-select my_packagesource ~/ros2_ws/set up/setup.bashros2 launch my_package obstacle_avoidance.launch.py
Associated programs & additional hyperlinks:
The put up Exploring ROS2 with a wheeled robotic – #4 – Impediment Avoidance appeared first on The Assemble.
The Assemble Weblog
[ad_2]