(Photograph courtesy of Dick Hack.)

Pallet valves operated by piano wippens in National coin piano (serial number unknown). This strip of wood with the fifteen individual pallet valves (mounted on the top cover for the National built stack) is used to generate randomized pneumatic signals. Approximately every forth valve is teed together, resulting in just four rubber tubes that represent the combined output signals generated by the individual pallet valves. These four tubes are connected to the Geneva gear driven randomizer module mounted on the “keybed” area of the piano. From the intervening mechanical randomizer device the four signals are transmitted via rubber tubing to a small valve chest underneath the race track. Each of the connected valves is further connected to one of the locking control pneumatics that, when activated, pull back the locking pawls interacting with the toothed rim of the Whippet drive pulleys. As such, each time a randomized pneumatic signal triggers a locking control pneumatic to collapse, unlocking the drive pulley, the affected Whippet will be momentarily propelled down the race track in a spurt of activity. But the length of activity is also randomized, according to the musical notes being played for the fifteen highest notes in the mid or tenor section of the piano. And so whether a signal to activate a specific Whippet is generated, or not, is random, as is the duration of the activating signal. This independent individualization of activity between the four Whippet hounds produces a Whippet race that will have a different outcome for each race, whether, or not, the same tune is being played over and over again.

(Photograph courtesy of Dick Hack.)

Mechanical randomizer module with intermediate gear drive in National piano #348. For this style of randomizer module a spur gear with a chain sprocket hub drives a second geared shaft that turns the pinned drive wheel that engages the much larger driven Geneva stepping gear. There are set screws in the top of what might appear to be "bearing" posts that are used to prevent the shaft from rotating. The left half of the metal randomizer drum has a set screw in its hub that locks it to the shaft, making this part of the randomizer mechanism stationary. The movable right half rides freely on the shaft and is driven by the Geneva stepping gear. There are four input tubing connections (from the piano wippen operated pallet valves) and four output tubing connections (going to a small valve chest underneath the race track). Every time the Geneva drive steps the movable drum into a new position the internal passageways within the two randomizer halves are rearranged. This additional level of randomization is totally independent of whatever music might be playing. Thus, the primary randomized signal generated by the piano action operated pallet valves, plus the further mechanical randomization, more or less guarantees that no signal pattern is repeated, no matter what musical selection might be played.

(Photograph courtesy of Dick Hack.)

Mechanical randomizer module with directly driven Geneva drive wheel in National piano #7352. This style of randomizer module functions identically to the above described style, except that there are no intermediate spur gears, the pinned Geneva drive wheel is mounted on one end of the the chain sprocket driven shaft, which engages the much larger fourteen-position driven Geneva gear. In this photograph the four input and four output nipples have rubber tubes connected to them. This simpler style was probably popular due to its less costly construction.

(Photograph courtesy of Dick Hack.)

The Whippet race valve chest and locking control pneumatics in National piano #7352. Looking at the bottom side of the Whippet race framework, the small valve chest at left contains five separate valve functions. Four of the valves are used for the locking control pneumatics, which are visible at picture right. The valve pouch control tubes for these valves connect to the mechanical randomizer module. The pouch control rubber tube going beyond the locking pneumatics connects to the finish gate elbow type pallet valve, while the controlled tube connects to the pneumatic that disengages the jaw clutch for the worm gear powering Whippet drive pulleys, an action that instantly terminates any further Whippet race activity.

(Photograph courtesy of Dick Hack.)

Whippet race valve chest connections in National piano #7352. Looking up at the valve chest in the Whippet race diorama, the four smaller rubber tubes dangling downward connect directly to the mechanical randomizer module mounted on the "keybed" area shelf. The large rubber tube connects directly to the player system vacuum supply.

(Photograph courtesy of Dick Hack.)

Whippet hounds sneaking along underneath the race track in National piano #7352. Here two Whippet hounds can be seen inching along upside down underneath the race track. Above them are three of the locking control pneumatics that pull the locking pawls away from the toothed rim of the Whippet drive pulleys. The starting gate is at picture right, and is still partially open because the tail end of one slow Whippet has yet to fully clear the gate.