Drives in theatres
28 February 2019

There are still a few places in the world where you can go to see plays as they were done two thousand years ago: half-ruined, open-air amphitheatres in which actors without mics declaim on stages without scenery. To witness such a performance is to realise at once how great a role technical stagecraft plays in the shows we enjoy on Broadway or in the West End.

In fact, we are unlikely ever to have seen a theatrical production that did not involve at least some simple lighting effects or visual variation of a scene. And – given that theatres are spaces dedicated to the imagination – we naturally, on occasion, bring to them expectations of the spectacular: magic carpet rides, collapsing houses, ghosts. Even the Elizabethans had a machine for lowering gods down from the sky.

The automation of a stage

In many respects, the nature of stage machinery has changed little over the years. Ropes and pulleys – the rigging – have been a staple of behind-the-scenes magic for centuries, as have such features of the lower stage as wheeled scenery wagons and revolving platforms. Traditionally all of the hoisting, pushing and turning was done by hand. Ropes used to be marked with little ribbons to show the stagehands when to stop pulling, just as tape marks on the floor would indicate the position into which a piece of scenery should be pushed.

The two great changes that revolutionised this kind of stagecraft were motorised power and, later, digital control systems. Drum winches and other devices powered by motors were originally controlled by simple stop and start buttons: a labour-saving innovation, but only as reliable as the individual operator in charge, still essentially uncoordinated with other stage activity and not, of course, variable in speed.

Programmable drives are now the standard way of controlling how far, how quickly, how precisely and how safely all visible components of a stage set move. And because they are networked together under the overall control of a central operating system, they act in concert with each other.  

A typical West End theatre might use upwards of 50 AC drives twinned with servomotors to control the overhead winches, and about half the same again for lifts and other devices in the lower stage. The devices are equipped with encoders, in order to maximise precise positioning and speed control, and with integrated emergency stop relays.

More than in most industrial contexts, the automation system in a theatre must be highly discreet: noise levels or movements that might otherwise be unobtrusive are in this space potentially distracting. Manufacturers of stage motors, therefore, aim to get them as compact and noiseless as possible without sacrifice of control.

Variable speed drives and servomotors in stage and theatre automation

Specially designed theatre winches, for example, might use permanent magnet servomotors and high-frequency 16kHz switching with dampened magnetic braking in order to eliminate almost all noise. And being able to exert full torque at low speed prevents something like a flybar from dropping after the brake release in a way that might take the audience’s attention off the imaginative experience.

The programming of each drive is tailored to the needs of the production of the moment: from lifting a lighting array, to lowering a trapeze bar, to repositioning a moveable onstage wall. When called upon by the control system to do so, the drives work together to achieve these effects simultaneously.

Control systems built from ladder logic and PLCs are being superseded in the world of theatre automation by PC-based operating systems written in specialised languages. These programs consist of commands, or cues, that are written within rules and parameters designed to ensure their safe and coordinated execution. The automated elements of an entire show can play out from start to finish according to such a program with proceedings overseen from a touchscreen console featuring a manual override facility for tweaking speed and maintaining synchronicity.

Compact, quiet, remotely monitored: drives and motors are liberating the theatre from conventional, and now seemingly outmoded, ways of working. After all, the idea that a stage should be set into the back wall of a theatre, framed like a picture by the proscenium arch, came about partly as a way of hiding large spaces adjacent to the stage (the wings and the overhead fly loft) in which rigging and scenery could be stowed and manipulated by teams of stagehands.

Improving experiences through stage engineering

Now that stage effects can be accomplished without the need for heavy manual labour, the stage itself may be brought more out into the open. It is a significant part of the movement towards today’s more ‘immersive’ kind of theatre. Increasing use is being made of traverse and thrust stages which project out into the bodies of auditoriums: the action, surrounded by the audience, takes place under a grid in which the motorised rigging system operates.

In such a set-up the automation engineer must work with new economies of space. Over the new thrust stage of the Royal Shakespeare Theatre in Stratford-upon-Avon, for example, the number of rigging opportunities has been doubled by using paired cable drums, each pair controlled by one drive and able to work together or independently of each other.

The versatility of this kind of stage engineering flows ultimately from the capacity of the drives to be programmed to support whatever automation program is written for any given show. Equally importantly, however: once that program is written, it is reproducible night after night – a guarantee of technical consistency that theatres of the past were unable to offer.

It is, in its own way, a new chapter in the history of stagecraft. It is also a reminder that the possibilities of automation are as responsive to the creative imagination as they are to the business of industry. That said, of course, in the case of the theatre they are already revolutionising both.

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