Most Frequently Asked Robot Operating System (ROS) Interview Questions
- What experience do you have working with ROS?
- What is your approach to debugging an issue in ROS?
- Describe a challenging problem you solved using ROS?
- How would you go about testing an algorithm in ROS?
- Can you explain the core concepts and components of ROS?
- What challenges have you encountered in developing ROS applications?
- How proficient are you in working with different ROS libraries?
- How familiar are you with both conventional and non-conventional ROS software?
- What do you think are the key differences between ROS and other Robotics middleware?
- How well do you understand ROS safety controllers and fault tolerance systems?
- How do you design and build ROS tools for real-world scenarios?
- Are you comfortable working with ROS code written in different languages?
What experience do you have working with ROS?
I have been working with the Robot Operating System (ROS) for over two years now. I have used ROS to develop a wide range of robotic and embedded applications. From controlling a simple two-wheeled motorized robot to programming an autonomous quadcopter, I have implemented various projects using ROS.One of the projects I am most proud of is a home security system I developed using ROS. This system was designed to detect intruders and alert the homeowner using push notifications. It included a network of motion sensors, infrared sensors and servos programmed to actuate a door lock. I used ROS to manage the whole project, from writing the necessary code to control each sensor and servo, to connecting the nodes with the master node which would enable remote access to the system.
Below, is a snippet of the ROS master node code that I wrote for the system:
#include "ros/ros.h"
...
int main(int argc, char **argv)
{
ros::init(argc, argv, "home_security_node");
ros::NodeHandle n;
ros::Rate loop_rate(10);
ros::Subscriber intruder_sub = n.subscribe("/intruder_topic", 1000, intruderCallback);
ros::Publisher notification_pub = n.advertise<std_msgs::String>("/notification_topic", 1000);
while (ros::ok())
{
// Check if intruder detected
if (intruderDetected)
{
//Sends push notification to homeowner
sendNotification();
}
ros::spinOnce();
loop_rate.sleep();
}
return 0;
}
What is your approach to debugging an issue in ROS?
When debugging an issue in ROS, the process starts with identifying the symptoms and pinpointing the source of the issue. After that, one should isolate the issue from the other side effects and decide on the corrective action that needs to be taken.To do this, it is important to use the various tools available in ROS for debugging, such as logfiles, roslaunch, rqt_console, and rosbag. Additionally, you can use a simple shell script to automatically print out the stack trace of any ROS nodes that have crashed. Similarly, using the roswtf command will help you identify any errors in the configuration of your ROS system.
For more complex issues, it may be necessary to resort to utilizing code snippets. In this case, one should take advantage of the interactive Python debugging capabilities by adding the following snippet at the beginning of the script in question:
import pdb; pdb.set_trace()This statement will set a breakpoint at that line, allowing the user to step through the code one line at a time. Additionally, the user can modify values at runtime, providing insights that would otherwise be difficult to find.
Finally, ROS provides debugging APIs such as rosservice and rosnode to analyze the state of your system. With these tools, one can view information about topics, services, and nodes, as well as inspect the values of variables at certain points in the code.
By taking advantage of all these tools, it is possible to debug an issue quickly and efficiently in ROS.
Describe a challenging problem you solved using ROS?
Recently, I solved an intriguing problem using the Robot Operating System (ROS). The challenge was to program a robotic arm to pick up a block and place it on a designated platform. The code below shows how I used ROS to handle this task.
```
#include <ros/ros.h>
#include <geometry_msgs/Pose.h>
#include <moveit/move_group_interface/move_group_interface.h>
int main(int argc, char **argv) {
// initialize ROS node
ros::init(argc, argv, "pick_and_place_node");
// create NodeHandle
ros::NodeHandle nh;
// create MoveGroupInterface instance
moveit::planning_interface::MoveGroupInterface group("group_name");
// set goal pose
geometry_msgs::Pose goal_pose;
goal_pose.position.x = 0.0;
goal_pose.position.y = 0.0;
goal_pose.position.z = 0.1;
goal_pose.orientation.w = 1.0;
// set planning time
group.setPlanningTime(15.0);
// set goal pose
group.setPoseTarget(goal_pose);
// move arm
moveit::planning_interface::MoveGroupInterface::Plan plan;
bool success = group.plan(plan);
// execute motion
if (success)
group.move();
return 0;
}
```
The above code snippet was used to create a plan for the robotic arm to reach its desired goal pose. I then ran the code, which successfully executed the motion of picking up the block and placing it on the designated platform.This was a challenging problem as it required me to accurately define the goal pose of the robotic arm, as well as taking into account the dynamics of the robotic arm. Additionally, I had to tune the parameters of the motion planner to achieve a successful path. In the end, I was able to successfully program the robotic arm to perform the task, providing a great level of satisfaction.
How would you go about testing an algorithm in ROS?
The most effective way to test a ROS algorithm is to use a combination of manual and automated testing processes. For manual testing, you would first need to create a test environment by simulating the desired environment in which the robot algorithms will be tested in. This can be done by creating a simulation in Gazebo or a test arena where the robot can be moved and interacted with objects.Once the test environment is created, you would need to write an appropriate test script for the algorithm. The test script should include the parameters needed for the test and the expected behavior of the robot during the test. Finally, you would need to run the script on the robot in the created test environment.
For automated testing, it is possible to use a ROS package such as rosbuster to automatically launch tests against your algorithm. The package allows you to define a comprehensive test suite with different configuration files for each test and execute them from the command line. Additionally, using rosbuster makes it possible to integrate the testing process into the continuous integration process.
In order to test an algorithm in ROS, you would need to create a test environment, write an appropriate test script, and then execute it with the desired parameters. Using rosbuster provides an automated solution to testing algorithms, allowing for easy integration into the workflow.
Here is a sample code snippet that can be used to test the algorithm:
```
#include <ros/ros.h>
#include <gtest/gtest.h>
int main(int argc, char **argv)
{
ros::init(argc, argv, "algorithm_test");
::testing::InitGoogleTest(&argc, argv);
return RUN_ALL_TESTS();
}
TEST(AlgorithmTest, MoveRobot) {
// Add logic to test algorithm behavior
}
```
Can you explain the core concepts and components of ROS?
ROS (Robot Operating System) is a middleware open-source software framework designed to enable users to create robotic applications. It provides the data, tools, and libraries needed for developing robot software. ROS consists of several core components:- Packages:
ROS packages are collections of software components that are related and used together to fulfill a single purpose. A package can contain code, configuration files, and other resources needed by the application.
- Messages:
ROS uses messaging as a means to enable communication between nodes. Messaging enables the description of state (sensors, parameters, etc.) and commands (motor control, etc.) to be shared across nodes in a distributed system.
- Nodes:
ROS nodes are the entities that compose a distributed system. Nodes communicate with each other using messages.
- Services:
Services are a way for nodes to offer additional functionality to other nodes in the system. They are synchronous, request/response based communication methods between nodes.
- Topics:
Topics are a form of publish/subscribe messaging that allow nodes to communicate with each other.
An example of a working ROS node written in Python might look like this:
import rospy
from std_msgs.msg import String
def talker():
pub = rospy.Publisher('chatter', String, queue_size=10)
rospy.init_node('talker', anonymous=True)
rate = rospy.Rate(10) # 10hz
while not rospy.is_shutdown():
hello_str = "hello world %s" % rospy.get_time()
rospy.loginfo(hello_str)
pub.publish(hello_str)
rate.sleep()
if __name__ == '__main__':
try:
talker()
except rospy.ROSInterruptException:
pass