ROS

Question 1

Define ROS

Answer 1

Robot operating system
-a flexible framework for writing robot software
-provides tools and libraries that simplify the task of creating robust robot behaviour

Question 2

Define the ROS ecosystem

Answer 2

the comprehensive and interconnected sets of tools,libraries and contributions

Question 3

Give the key components of ROS

Answer 3

ROSCORE - a collection of essential services including ROS master
Communication infrastructure - nodes and topics

Question 4

What are the two ROS communication methods

Answer 4

-Publisher- subscriber communication
-Client server communication

Question 5

Explain how Publisher-subscriber communication works

Answer 5

-A publisher node creates a topic and sends message to that topic
-a subscriber node subcribes to the topic and receives the message
-ROS ensures that messages are delivered efficiently and reliably

Question 6

Explain how client server communication works

Answer 6

-Client node sends a request to the service server and awaits response
-Service node offers service and awaits requests, processes them and sends them back
-a service definition is used to initialise data

Question 7

Give characteristics of publisher-subsriber communication

Answer 7

-Asynchronous
-ideal for continuous data
-Many to many: multiple publisher nodes can send to a topic and multiple subscriber nodes can receive from a topic
-publishers and subscribers do not need to know each other, just agree on same topic

Question 8

Give characteristics of client server communication

Answer 8

-Synchronous (immediate response)
-One to one: one client communicates with one server per request
-

Question 9

Give an example of publisher-subscriber communication application

Answer 9

Robot state updates:
-Robots current pose is sent to ‘/pose’ topic
-visualisation tool (RViz), subscribes to ‘/pose’ topic to display/log robots position

Question 10

Give an example of client server communication application

Answer 10

Robot manipulation:
-a client node requests joint pose of an arm using a ‘joint_request’ service
-the arm controller processes the request and sends confirmation once movement is complete

Question 11

Define a URDF

Answer 11

Universal robot description format
-used for visualisation processes

Question 12

In terms of ROS, define a package

Answer 12

the basic unit of ROS
contains a configuration file to launch other packages or nodes
metapackage contains a set of common purpose packages