The root link base_link has an inertia specified in the URDF, but KDL does not support a root link with an inertia
<robot name="robot_kol">
<link name="base_link">
<inertial>
<origin xyz="0 0 0" rpy="0 0 0" />
<mass value="1.46872860183279" />
<inertia ixx="0.337078234151496" ixy="0.000400956172161471" ixz="0.000153729345332478" iyy="0.323323767647255" iyz="-0.00436480886180004" izz="0.0204387896128557" />
</inertial>
<visual>
<origin xyz="0 0 0" rpy="0 0 0" />
<geometry>
<box size="0.1 0.1 0.1"/>
</geometry>
<material name="">
<color rgba="0.780392156862745 0.76078431372549 0.741176470588235 1" />
</material>
</visual>
<collision>
<origin xyz="0 0 0" rpy="0 0 0" />
<geometry>
<box size="0.1 0.1 0.1"/>
</geometry>
</collision>
</link>
<link name="LKL1">
<inertial>
<origin xyz="0 0 0" rpy="0 0 0" />
<mass value="0.107409280317998" />
<inertia ixx="0" ixy="0" ixz="0" iyy="0" iyz="0" izz="0" />
</inertial>
<visual>
<origin xyz="0 0 0" rpy="0 0 0" />
<geometry>
<box size="0.03 0.03 0.03"/>
</geometry>
<material name="">
<color rgba="0.780392156862745 0.76078431372549 0.741176470588235 1" />
</material>
</visual>
<collision>
<origin xyz="0 0 0" rpy="0 0 0" />
<geometry>
<box size="0.03 0.03 0.03"/>
</geometry>
</collision>
</link>
<joint name="JKL1" type="revolute">
<origin xyz="-0.119911595296941 0 1.2673449974201" rpy="0 0 1.5707963267949" />
<parent link="base_link" />
<child link="LKL1" />
<axis xyz="0 -0.950178193313767 -0.311707235961865" />
<limit lower="-4.18719" upper="-1.045605" effort="17000" velocity="45" />
</joint>
<link name="LKL2">
<inertial>
<origin xyz="0 0 0" rpy="0 0 0" />
<mass value="0.103899926184644" />
<inertia ixx="0" ixy="0" ixz="0" iyy="0" iyz="0" izz="0" />
</inertial>
<visual>
<origin xyz="0 0 0" rpy="0 0 0" />
<geometry>
<box size="0.03 0.03 0.03"/>
</geometry>
<material name="">
<color rgba="0.780392156862745 0.76078431372549 0.741176470588235 1" />
</material>
</visual>
<collision>
<origin xyz="0 0 0" rpy="0 0 0" />
<geometry>
<box size="0.03 0.03 0.03"/>
</geometry>
</collision>
</link>
<joint name="JKL2" type="revolute">
<origin xyz="-0.0300007513110643 0.0481697030691494 0.0312158251163472" rpy="0 0 0" />
<parent link="LKL1" />
<child link="LKL2" />
<axis xyz="-1 0 0" />
<limit lower="-1.57079" upper="0.0" effort="17000" velocity="45" />
</joint>
<link name="LKL3">
<inertial>
<origin xyz="0 0 0" rpy="0 0 0" />
<mass value="0.107409280317999" />
<inertia ixx="0" ixy="0" ixz="0" iyy="0" iyz="0" izz="0" />
</inertial>
<visual>
<origin xyz="0 0 0" rpy="0 0 0" />
<geometry>
<box size="0.03 0.03 0.03"/>
</geometry>
<material name="">
<color rgba="0.780392156862745 0.76078431372549 0.741176470588235 1" />
</material>
</visual>
<collision>
<origin xyz="0 0 0" rpy="0 0 ...