Explaining the xacro model of the seven DOF arm

We will define ten links and nine joints on this robot, and two links and two joints in the robot gripper.

Let's start by looking at the xacro definition:

<?xml version="1.0"?> 
<robot name="seven_dof_arm" xmlns:xacro="http://ros.org/wiki/xacro">  

Because we are writing a xacro file, we should mention the xacro namespace to parse the file.

Using constants

We use constants inside this xacro to make robot descriptions shorter and more readable. Here, we define the degree to the radian conversion factor, PI value, length, height, and width of each of the links:

  <property name="deg_to_rad" value="0.01745329251994329577"/> 
  <property name="M_PI" value="3.14159"/> 
  <property name="elbow_pitch_len" value="0.22" /> 
  <property name="elbow_pitch_width" value="0.04" /> 
  <property name="elbow_pitch_height" value="0.04" /> 

Using macros

We define macros in this code to avoid repeatability and to make the code...