both the hot side and the cold side are on one shaft and doing work at the same time in the same direction.
Since the inner cylinder of each row of cylinders is 180° apart of the 2 outer cylinders, you only get 4 independant power strokes .
Rombic Drive to minimize friction and side force on cylinder walls.
"W" configuration for 0 vibration.
Aranged in a "W" shape 60° apart.