from typing import List


def define_frontal_chest_direction(robot: str) -> List:
    """Define the robot-specific frontal chest direction in the chest frame."""

    if robot != "iCubV2_5":
        raise Exception("Frontal chest direction only defined for iCubV2_5.")

    # For iCubV2_5, the z axis of the chest frame is pointing forward
    frontal_base_direction = [0, 0, 1]

    return frontal_base_direction