Drives ensure the show must go on

The Queen fantasy musical, "We will rock you" features an imaginative and technically complex stage set which provided some complex motion control tasks for its designers.

The Queen fantasy musical, "We will rock you" launched in London's West End to rave critical reviews for the music, primarily, of course, but also for the imaginative and technically complex stage set.

The show opened at The Dominion Theatre on 14th May, which gave set designers Mark Fisher and Willie Williams a tight production schedule in the eight-week lead up to the innovative production - and even less time for scenery fabrication contractor Brilliant Stages and automation supplier Entertainment Innovations of Croydon.

Four separate projects were involved.

The movement, using a Serapid push-pull chain, of the High-School colonnade up and down the stage, the chain-driven movement of the set of the Tottenham Court Road tube station, control of four truck-driven video screens and, fourthly, the control of four flown video screens.

"We had to work to a very tight time schedule", says Andy Cave of Entertainment Innovations, the automation contractor chosen for the task, "and yet retain the ability to make changes right up to opening night.

So we chose Control Techniques Unidrives throughout, because of their flexibility in use and their ease of programming".

The Serapid chain, developed for the French nuclear industry, is a special design of chain with linear stiffness so that it can be pushed as well as pulled.

This is the duty of a Control Techniques 11kW Unidrive universal AC drive, running in servo mode and controlling a 190-frame Unimotor.

Using a plug-in coprocessor, the movements are programmed into the drive itself using a modified version of the Control Techniques LiPoS (linear positioning) software.

Actions are initiated by a signal from a CTIU low-cost, high specification operator interface, via a RS485 serial communication with the drive itself.

The set for the Tottenham Court Road Tube Station is moved into position with a more conventional chain and sprocket system, running in a slot on the stage.

The chain passes up and over a driven sprocket on the set itself.

A custom-made controller communicates with the digital inputs on the UD75 onboard coprocessor on the 7.5kW Unidrive.

The four video trucks, with several thousands worth of high-intensity video screens, are each independently controlled by a stagehand using a simple, multiposition purpose-built hand control.

Each truck has a 2.2kW Unidrive controlling the height of the screen via a Unimotor and Alpha LP120 gearhead.

An onboard UD75 coprocessor provides the programming, using commands from a simple handheld controller to recall preprogrammed positions stored in the drive.

A further four high intensity LED screens, each about 1.5m wide by 2.3m high, are supported by trolleys, driven by 0.75kW Unidrives on a rack and pinion system up and down an I beam bolted to the underside of a truss hung above the stage.

Each screen weighs around 300kg and is lifted by a winch powered by a networked 7.5kW Unidrive system.

Producing very bright and intense colours and video images, the screens can be moved with great accuracy to give a continuous screen or four separate screens at different heights.

The video trucks can also be manoeuvred into position beneath the flown video screens to form one big eight-section screen across the stage.

Cues are stored in the drives and recalled using a Control Techniques operator interface via Control Techniques' high-speed network CT-Net, using LiPoS linear positioning software within each drive's co-processor unit.

A special version of LiPoS was produced allowing up to 64 separate positions to be stored, along with individual move speeds and ramps.

Digital lock between the drives proved to be unnecessary because of the accuracy of the LiPoS system, simplifying the development time of the commissioning and trials to just a few days.

The drives system is mounted into a space-saving 19in rack-mount system, for ease of access.

The strength of LiPoS is in its flexibility, that allows preset or serial communication controlled moves, in discrete, triggered or automatic sequences, as well as continuous following, giving the client a wide variety of control options.

LiPoS offers up to 100 preloadable programmable move profiles, independent profile acceleration, deceleration, maximum travel speed and post-move dwell.

Linear moves are programmed in user units.

Move lengths up to 32m and resolutions down to 1um can be set up, with variable target window accuracy and settling time.

It is simple to set up torque and force limits, alarms and outputs can be set both for overall limits and to control individual moves.

The program is packed with features - including travel limits and absolute positioning - with all of the programming being set up either from the drive display, or using Control Techniques' SyPT toolkit from a PC.

"The LiPoS program is flexible enough to allow artistic changes to be made in just a couple of minutes without complex programming", comments Andy Cave, "which proved to be very welcome in the run up to the show launch, with changes being made almost every day".

The Unidrive range of AC drives spans capacities from 0.75kW to 1MW and five operating modes including servo mode.

With plug-in modules, the drive can be tailor made to fit a vast range of different applications, with most of the industry-standard network protocols as well as Control Techniques' own high-speed network, CT-Net, used in this application.

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