hexapod_robot/hexapod_robot.xml

<library path="hexapod_robot_hwi">
    <class name="hexapod_robot/HexapodRobotHardwareInterface"
           type="hexapod_robot::HexapodRobotHardwareInterface"
           base_class_type="hardware_interface::SystemInterface">
        <description>Hexapod Hardware Interface</description>
    </class>
</library>