diff --git a/urdfpy/urdf.py b/urdfpy/urdf.py
index 8536e39..7aaf915 100644
--- a/urdfpy/urdf.py
+++ b/urdfpy/urdf.py
@@ -2306,15 +2306,11 @@ def get_child_pose(self, cfg=None):
         elif self.joint_type in ['revolute', 'continuous']:
             if cfg is None:
                 cfg = 0.0
-            else:
-                cfg = float(cfg)
             R = trimesh.transformations.rotation_matrix(cfg, self.axis)
             return self.origin.dot(R)
         elif self.joint_type == 'prismatic':
             if cfg is None:
                 cfg = 0.0
-            else:
-                cfg = float(cfg)
             translation = np.eye(4, dtype=np.float64)
             translation[:3,3] = self.axis * cfg
             return self.origin.dot(translation)
@@ -2538,7 +2534,7 @@ def inertial(self, value):
             raise TypeError('Expected Inertial object')
         # Set default inertial
         if value is None:
-            value = Inertial(mass=1.0, inertia=np.eye(3))
+            value = Inertial(mass=0.0, inertia=0.*np.eye(3))
         self._inertial = value
 
     @property