Patent US 4,130,168

A self-contained, portable, extensible boom assembly for detachable mounting on a vehicle such as on the open top box body of a truck has power driven boom actuating mechanism and downcrowding storage mechanism activated by said power driven mechanism for maintaining a downcrowding load on a driver tool suspended from the boom together with mechanism for controlling the extension of the boom to maintain a straight line alignment of the tool as it advances under the downcrowding load. The portable with mechanism for controlling the extension of the boom to maintain a straight line alignment of the tool as it advances under the downcrowding load. The portable self-contained assembly can carry its own power source such as a battery or can be driven through a power take-off from the engine of the truck on which it is mounted. The assembly is unitary, relatively light in weight, easily transported, and is easily mounted on and removed from a truck vehicle without altering the construction of the vehicle.