Stage set for faultless performance

GEARBOXES SUPPLIED by STOBER Drives, are regularly specified by theatre supplier Absolute Motion Control for control systems that move props and scenery during performances.

'The Ocean at the End of the Lane', a National Theatre show running at the Duke of York’s theatre In London, needed automated lifts which incorporate servo motors, gearboxes and drives to elevate various stage design elements from below the floor to the stage. A key challenge was finding extremely quiet servo drive systems that would fit into tightly confined spaces.

A further challenge was to create these within a twelve-week lead time; not uncommon in the theatre business. To speed production, the motor and the gearbox are often specified before the design process is complete, which leaves the manufacturer free to overcome specific design issues relating to each show’s unique requirements. It also allows them to accommodate unknown factors as they occur.

Then, subject to the success of the show, the props may need to continue to work faultlessly for far longer than the initial run.

For this show, four lifts of differing specifications were required to raise and lower two door frames, a bench, and a bath weighing 850kg at 300mm/sec. The lifts cover vertical distances to the stage of between 450 to 2100mm for the various props.

Helical bevel gearboxes

Absolute Motion Control selected from the K Series of right-angle helical bevel ServoFit gearboxes, which can be fitted using tapped rather than through-holes on all sides of the gearbox. This makes it very easy to install them in tight spaces, and without the inconvenience of a nut and bolt, the engineer simply screws into a tapped hole.

On the door lifting mechanism, for instance, the gearbox turns a 30mm driveshaft with a chain sprocket that moves the platform, upon which the prop is mounted, up to the stage and down again at the end of the scene. There is also a secondary belt-drive to a Rotary Limit Box that is designed to protect the mechanics from over-travel.

During performances, the lifting systems are each controlled from a central control position by a stage engineer.

Typically, other show sets use these gearboxes to drive rotating steel floors, which currently is a very popular effect in the West End. In these applications, the dimensions and ratio of the gearboxes are key. For example, the automation mechanics are built to turn a 200mm to 300mm deep floor, and a STOBER K102 gearbox will deliver the power needed to do this. Its small size also means that it fits within the parameters of the floor, which are always tight.

Apart from the steelwork, the gearbox and the motor are often the largest aspects of the floor and, on a 200mm or 300mm thickness floor, the size, weight, ratio and power output of the gearbox has a huge impact on the budget and cost efficiency of creating the required motion.

Ben Phillips, of Absolute Motion Control says: "So many factors are taken into account in our partnership with STOBER. As well as the colour, we have found that the ratio of STOBER K series goes up to 70:1 (2 stage) and 271:1 (3 stage) , something we have found impossible to match from other manufacturers. Another important factor is the personal contact we enjoy from them, which gives a reliable and personal feel to their service. This makes STOBER much more user-friendly to theatre industry requirements."

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