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" />