Motor 310 may be reversible (permitting ???engine braking???) or it may ???free-wheel??? permitting carriage assembly 150 to return to the distal end of boom 120 under the weight of pipe in the trough, but it would in that embodiment typically be accompanied by a form of brake or clutch adapted to limit the acceleration of carriage assembly 150 as it returns to the distal end of boom 120. [0037] A