Letters from the Sandia Corporation on October 7 and 21, 1948 advised that nonspinning cable was absolutely necessary for the main hoist, to eliminate twisting or rotating of the load block during its unloaded travel up or down, The use of nonrotating wire rope for the main hoist made a single wrap winding drum necessary on the hoisting machine. Several wire rope manufacturers were consulted, and none of them would recommend maltiple wrapping of nonrotating wire rope on the drum. Because of the amount of rope to be handled, a rather large winding drum was required. A very extensive survey was made in an attempt to locate a standard make of hoist machine which would meet the rope capacity, line pull, and hoisting speed requirements, but no such machine could be located. It was then decided that a custom-built machine would have to be used. Inasmich as a single wrap drum was necessary for the main hoist machine, it was decided to use an identical drum on the skip hoist machine in order to keep the skip hoist and main hoist machines as similar as possible and reduce types of replacement parts to a minimum, The main hoist load block was substantially the same as that used on the Sandstone towers. Check weights were attached to the block to make its total weight 900 pounds. This was done to insure proper wrap- ping of the cable on the hoist drum under no-load operation. A main hoist top limit switch was mounted on top of the structural A-frame to stop the up travel of the load block when its clevis pin hole was 13 feet, 3 inches above the floor level of the tower house. This distance was established in the preliminery specifications furnished by the Sandia Corporation representative. All of the mechanical equipment for the 300 foot towers was installed at the Jobsite as shown on the drawings and covered in the specifications and operated satisfactorily at test time. The electrical design criteria, as stated by the Sandia representative, stressed smooth and positive operations of both the main hoist and the personnel skip hoist. For this service, the Ward Leonard system of control was selected, In this system of control, a direct-— current motor is used to drive the cable drum, and the speed of the motor is varied by varying the voltage applied to the armature of the drive motor. The variable voltage source is obtained from a motorgenerator set with the output of the generator exciter connected di- rectly to the drive motor field and through a rheostat to the genera- tor field. The voltage of the generator is then varied by adjusting the generator field rheostat. In addition to providing smooth operation, this system provides a means of obtaining regenerative braking, which is necessary to provide smooth deceleration. The actual control of speed of either equipment was by means of push buttons, up and down, faster and slower, which operated a reversible control motor driving the rheostat. 5-136