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It works because the air friction of the rods connecting the ball to the power wheel is higher when going down then when going up. And this happen because when the go upward, the rods are parallel to the movement so the surface is less than when its going downward (they are then in diagonal with the movement so more surface).

Ah, I understand.
But I think you mean that the horizontal surface of the bar is bigger then when he goed upwards, not that the airfriction is higher.