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ROS simulating a 3 axis robot in Rviz

In this tutorial, we will create an urdf model of a 3 axis robot and simulate it in Rviz.

Create a package inside your workspace (create it if u haven't any).

Create a folder named urdf to store urdf models.

Now create a new file called my_robot.urdf with these data.

This link will give you a list of all possible tag tags and informations. (Read this before going further. link) There are 4 links and three joints in this robot. Each joint has one parent and one child.
There are different types of joints. Here we used continuous and fixed type. Joint 0 is fixed and the rest of them are continuous. The origin tag inside the <joint> <origin rpy="0 0 0" xyz="0 0 3"/> represents the amount of offset required from the parent link. This can be clearly understood from the following figure.
There is also an another origin tag inside link tag. This represent the base frame of the link itself. We need to shift it by 1.5 (half of the link length), other wise rotation will be around the middle part of each link rather than at the joint (This will make sure both the base frame; child and parent coincides).
 


Now create a file called my_robot.launch under launch folder. This will launch joint_state_publisher and robot_state_publisher node. joint_state_publisher node will publish all the joint states. This also has one gui where you can change each joint angles. robot_state_publisher node will take the joint angles of the robot as input and publishes the 3D poses of each links. 
Now create another file called rviz.rviz. (This is not actually needed. This is just a configuration file for Rviz saying that these panels should be there. You can open rviz and add the RobotModel and save the configuration by yourself.)
Now launch the launch file.
If you are planning to create a hardware and want to simulate the same, you can create a separate node that will publish joint states instead of using joint_state_publisher node.

Here instead of actual hardware ESP8266 is communicating with ROS and sending joint angles of a 5 axis robot.

You can refer these tutorials to get more in depth knowledge.
http://wiki.ros.org/urdf/Tutorials
https://www.youtube.com/watch?v=g9WHxOpAUns
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