stack is complete 6 the operator stops forward motion of the harvester backs up to drop off the stack and re starts the robot the robotic auto stacker has some commercial advantages over alternative designs it is light weight and small fitting approximately within the envelope of a traditional tractor mounted sod harvester it is flexible the robot can be programmed to stack 16 or 24 inch wide sod rolls into stacks of different heights the pick up head has two features which can be used to stack the top two layers in a u201c pyramid u201d fashion the five grippers 70 on the pick up head can be squeezed together which will compress the row as it is placed on the stack also one of the five rolls can be dropped independently which allows you to stack the next to the last layer with two rows of five with two individual rolls turned sideways in between and the last layer with four rolls each the robot actually picks up and repositions one of these rows after it is initially placed in other words there is a high degree of flexibility in how the sod is stacked and a stable stack can be achieved without extra wrapping in addition to the small size and flexibility the machine is.