Theatre Design & Technology - Spring 1979 - 13

Royal Opera House for Wagner's cycle of operas Der Ring
des Nibelungen. The first performance of a new production of
this work by GCitz Friedrich, with set design by the Czech,
Josef Svoboda, under the musical direction of Colin Davis,
was to be in September, 1974. Rehearsals were planned for
August, leaving only three and a half months for the stage
design to be finalized and for all the engineering and manufacture to be completed to operational satisfaction.
Svoboda's very new visual interpretation set the criteria for
the engineering problem; he required a platform 12m square
which had to be totally mobile, supported only by a slender
central column 1.2m square. The platform had to move vertically to 4m above normal stage level at speeds up to 3m/min.,
rotate in either direction at up to 2 rpm, and incline to 45° in
both horizontal planes or compounds thereof. Besides supporting up to thirty-six performers at one time, the stage also
had to carry seven flights of power-operated stairs and a 15m
high tree; the total weight being in the order of ten metric
tons. [A metric ton equals approximately 1.1 U.S. tons.)
The particular difficulty was that most of the complex
movements for scene changes were to take place in full view
of the audience, with the performers in situ, and the various
multiple motions synchronized precisely with the musical
score. T he four totally independent movements had, therefore, to be able to take place both smoothly and silently;
further, they had to be repeatable to within close tolerances,
sometimes in almost total darkness.
The platform was constructed, in space frame form, of
rectangular box sections around the central support. The
complete set was to be demountable in four hours-essential,
as the repertoire of the Royal Opera House can change daily.
The platform was supported on a lattice braced tower constructed in three telescopic stages with fully machined
guides. Power was supplied by two purpose-built 125mm
bore, 4m stroke, single-acting, linear actuators, mounted
within the structure.
On the top of the column, a central gimbal assembly was
mounted incorporating a 1.3m diameter ball-bearing slewing
ring with an internal gear through which the platform was
rotated by a reduction gear, torque limiter, and fluid motor.
Four 100mm bore, 1.3 stroke, double-acting cylinders, again
purpose built, were used to provide the inclination movement
in the two planes, operating in push-pull pairs. Weighing a
total of 2.25 metric tons, the complete gimbal assembly could
be rapidly disconnected from the column and removed on a
special wheeled cradle.
The platform skeleton was covered in various scenic panels dependent on the individual production. In addition, for
Die Walkure, Siegfried, and Gotterdammerung, a diagonal
ramp was built into the platform structure, 2m wide, 7m long,
and pivoted at one end. It could be hydraulically raised up to
20° to the platform surface. Two single-acting actuators were
used for power. The underside of the platform was covered
with synthetic mirrors to reflect to the audience, action in the
'underworld' below normal stage level.

Hydraulic Power Supply

In the basement, some 20 feet (6m) below stage level,
hydraulic power for all the movements was supplied by completely independent power packs. Each of these packs comUSITT/Spring, 1979

prised a 10hp (7A6kW) unit for elevation, three 7.5hp
(5.59kW) units for inclination and rotation, and a single 2hp
(1.5kW) unit for the ramp and incorporated a variable-volume, pressure-compensated vane pump, with an acoustic
tuning facility. The pumps used were Vickers Racine Supervane type, which are qUiet in operation and are thus a natural
choice for theatrical applications. Flow from the pumps was
pulse-suppressed before the Series 60 valves supplied the
final control stage. Total noise output was within NC20.
Control of the various movements was achieved by using
five independent control boxes, each some 12" (305mm) long
by 3" (76mm) square. Made of aluminum, they were light
enough to be hand-held. Each controller incorporated a key
switch (only selected and trained operators were allowed to
use the equipment), a power unit on/off switch with run light,
a proportional control lever, and a four-digit electronic position read-out connected to position potentiometers on the
actuators and fluid motor.
It was thus possible for precise 'cueing' instructions to be
incorporated into the musical score; the instructions being
relayed to the two or three controllers who were operating the
set from different locations by the prompter. Each digital
indicator could read from 0-2000 and it was thus possible to
control the platform to an accuracy of one part in 2000 of its
total movement on any of the five channels.

The National Theatre

The National Theatre on London's South Bank has a permanent stage elevator system built into one of its three auditoriums. This particular stage, at the 890-seat Lyttelton
Theatre, has been constructed on a modular pattern using
interchangeable 2X 1m steel-framed floor sections. The total
stage area is 22m wide by 16m deep and is capable of
sustaining a static payload of 750 kgf/m 2 *
The forward part of the stage is divided into three sections,
each of which can be individually raised OAm above stage or
lowered 3.5m below stage at infinitely variable speeds up to
14m/min. The main section of the stage, measuring
13.6X 12m can be raised or lowered by approximately 1m.
The speed is infinitely variable up to 3m/min. and the stage
can be raked up to a maximum gradient of 12'/2%. A total
dynamic payload of 50 metric tons can be carried.
Traditionally this type of stage elevator would be supported
and moved by screw mechanisms, or direct-acting hydraulic
rams. However, a major requirement for the design of this
system was variable and precise speed control-possible but
expensive with existing electrical drives-while the size of
shafting required for driving and synchronization of the
movements of the individual stage sections would have also
been excessive in relationship to the space available.
The problem was solved by a new device termed a screw
ram, of which seven are used in the National Theatre application. Each comprises a conventional single-acting hydraulic ram, the actuating rod of which is in the form of a screw.
This engages with a bronze nut. The nut is restrained between
ball thrust bearings and the helix angle of the thread equates
precisely with the angle of friction for the bronze-to-steel
interface. A worm wheel is concentrically fixed to the nut and
meshes with the worm shaft, the drive stub of which protrudes from the gear box in a conventional manner.
Theatre Design & Technology

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