A paint ball simulation toy including a number of darts, a launcher configured to propel the darts, and a number of stickers each carried by a dart and configured to simulate a paint ball strike. Since the moments Ma, Mb about the centroid generated by the thrusts cancel each other and the thrusts do not act as forces for rotating the Y-direction stage, the Y-direction stage is not deflected in a yawing direction. The method may also include positioning a cold plate of a room-level cooling system in thermal contact with the hot plate. The central axis of the valve seat member is positioned outside the mouth edge.