diff --git a/urdf_parser_py/src/urdf_parser_py/urdf.py b/urdf_parser_py/src/urdf_parser_py/urdf.py
index b0fceb02..0c4eb8bb 100644
--- a/urdf_parser_py/src/urdf_parser_py/urdf.py
+++ b/urdf_parser_py/src/urdf_parser_py/urdf.py
@@ -224,8 +224,8 @@ def __init__(self, rising=None, falling=None):
 		self.falling = falling
 
 xmlr.reflect(JointCalibration, params = [
-	xmlr.Attribute('rising', float),
-	xmlr.Attribute('falling', float)
+	xmlr.Attribute('rising', float, False),
+	xmlr.Attribute('falling', float, False)
 	])
 
 class JointLimit(xmlr.Object):
@@ -237,8 +237,8 @@ def __init__(self, effort=None, velocity=None, lower=None, upper=None):
 
 xmlr.reflect(JointLimit, params = [
 	xmlr.Attribute('effort', float),
-	xmlr.Attribute('lower', float),
-	xmlr.Attribute('upper', float),
+	xmlr.Attribute('lower', float, False, 0),
+	xmlr.Attribute('upper', float, False, 0),
 	xmlr.Attribute('velocity', float)
 	])
 
@@ -264,9 +264,9 @@ def __init__(self, velocity=None, position=None, lower=None, upper=None):
 
 xmlr.reflect(SafetyController, params = [
 	xmlr.Attribute('k_velocity', float),
-	xmlr.Attribute('k_position', float),
-	xmlr.Attribute('soft_lower_limit', float),
-	xmlr.Attribute('soft_upper_limit', float)
+	xmlr.Attribute('k_position', float, False, 0),
+	xmlr.Attribute('soft_lower_limit', float, False, 0),
+	xmlr.Attribute('soft_upper_limit', float, False, 0)
 	])
 
 class Joint(xmlr.Object):
@@ -339,10 +339,10 @@ def __init__(self, name = None, joint = None, actuator = None, type = None, mech
 
 xmlr.reflect(Transmission, tag = 'transmission', params = [
 	name_attribute,
-	xmlr.Attribute('type', str),
-	xmlr.Element('joint', 'element_name'),
-	xmlr.Element('actuator', 'element_name'),
-	xmlr.Element('mechanicalReduction', float)
+	xmlr.Attribute('type', str, False),
+	xmlr.Element('joint', 'element_name', False),
+	xmlr.Element('actuator', 'element_name', False),
+	xmlr.Element('mechanicalReduction', float, False)
 	])
 
 class Robot(xmlr.Object):
@@ -433,4 +433,4 @@ def from_parameter_server(cls, key = 'robot_description'):
 # Make an alias
 URDF = Robot
 
-xmlr.end_namespace()
\ No newline at end of file
+xmlr.end_namespace()