What is ROS ?

A lot of people are still confused about the concept of ROS which includes both those who use them and those who don't. Robot Operating System is an open-source robot middleware platform that provides hardware abstraction, device drivers, and many useful libraries and tools to develop robot applications. Developed in 2009, initially for the use with the Willow Garage PR2 robot, ROS has now a large community of developers and users.

This community has developed important general-use libraries for motion planning, task execution, 2D navigation, and visualization and a lot more that has proved invaluable standards in robotics research. Despite its many advantages, ROS has several shortcomings with regards to usability, portability, and platform dependencies. For ROS, the officially supported operating system is Ubuntu, a popular Linux distribution. All these problems are now solved in the second version called ROS2.

ROS has a microkernel design where a large number of small tools are used to build and run various components. A ROS system consists of a number of processes called nodes which are connected in a peer-to-peer network topology. Nodes perform the system’s computation and communicate with other nodes in ROS by exchanging messages, which may contain a single primitive or complex data structure. Messages can be composed of arrays of other messages. A node sends a message by publishing it into a given topic.

ROS provides two types of messaging mechanisms called topic and service. The topic is a pub/sub based asynchronous message type. A publisher broadcasts topic messages to the system, while the subscribers listen to the published information on this topic. There may be more than one publisher or subscriber for the same topic and a single node may publish and/or subscribe to multiple topics.

On the other hand, service is request and response based synchronous message type. It is defined by a string name and a pair of strictly typed messages: one for the request and one for the response. Unlike the topic, there is only one node that can advertise the service of any particular name.
ROS software system is organized into packages. A ROS package is simply a directory that contains an XML file describing the package and stating its dependencies. This packaging system is meant to build ROS based software into small, manageable chunks, each of which can be maintained and developed on its own schedule by other developers.

References :
1. Quigley, M., Conley, K., Gerkey, B., Faust, J., Foote, T., Leibs, J., Wheeler, R. and Ng, A.Y., 2009, May. ROS: an open-source Robot Operating System. In ICRA workshop on open source software (Vol. 3, No. 3.2, p. 5).
2. Toris, R., Kammerl, J., Lu, D.V., Lee, J., Jenkins, O.C., Osentoski, S., Wills, M. and Chernova, S., “Robot web tools: Efficient messaging for cloud robotics. In Intelligent Robots and Systems (IROS)”, 2015 IEEE/RSJ International Conference on (pp. 4530-4537). IEEE.

Comments

Post a Comment

Popular posts from this blog

The move_base ROS node

Image
move_base package provides the move_base node which is a major element of ROS Navigation stack. It moves the robot from its current position to a goal position. When path planning is done, the user gives uses the 2D Nav Goal in RVIZ to specify the goal position and orientation. This position (x,y,z) and orientation(x,y,z,w) are actually published in move_base/goal topic. The move_base node links together a global and local planner to accomplish its global navigation task. The Global Planner It is in charge of calculating the safe path in order to arrive at goal pose. Note that the path is calculated before the robot starts moving so it will not take into account the laser readings while moving i.e. unscanned obstacles that are not in the map. Navfn Planner The Navfn planner is the most commonly used global planner for ROS Navigation. It uses Dijkstra's algorithm in order to calculate the shortest path between the initial pose and the goal pose. Carrot Planner This plann...
Read more

Three Wheeled Omnidirectional Robot : Motion Analysis

Image
A Three-wheeled omnidirectional robot is capable to moving in any given direction without rotating by giving velocities to the three wheels in a certain ratio. All motors are situated at an angle of 120 degrees from each other. f B ,  f L ,  f R  are for back , left and right wheel respectively. a x  and a y  are accelerations in X R  and Y R  axis in Robot frame and w is the angular velocity in Robot frame. Hence putting the values of alpha and making it into a matrix form we get : As we need to obtain the f values, we will invert the matrix. We need  a x  , a y  and w is the world frame, so we apply transformation. The transformation angle is    α 1  = 30 degrees.  Putting this in the previous equation, Multiplying the two matrices, we get the final relation as : For example, if you want to move the robot along X axis(world frame), put  a x W  = 1 , ...
Read more

Overview of ATmega328P

Image
While reading about the ATmega328, I came a across a lot of stuff which I would like to share here. There is a humongous amount of information available in its datasheet. Introduction ATmega328 is a single chip micro-controller created by Atmel. It has a In-System Self-programmable Flash memory of 32 KB, SRAM of 2 KB (2048 bytes) and EEPROM of 1 KB (1024 bytes). It has a 8-bit AVR CPU type which means they can process data in 8-bit chunk as its data bus is 8-bit wide.   It contains 23 general purpose I/O pins and 32 general purpose working registers. It has 32 single-byte registers and 8-bit RISC (reduced instruction set computer) devices and hence the name 328. The P is for ' picoPower '. It has 3 flexible timer/counter with compare modes, internal and external interupts , 6-channel 10-bit A/D converter , programmable watch dog timer with internal oscillator and 5 software selectable power saving modes. Digital communication peripherals include 1-USART, 2-SPI and 1-...
Read more