The Olympic Cauldron in Sydney returns

On September 15, 2000, the largest television audience ever assembled watched athlete Cathy Freeman light the flame that opened the Games of the XVII Olympiad in Sydney, Australia. That flame may have been extinguished at the end of the games, but the Olympic Cauldron has reappeared in The Overflow, an area of parkland immediately adjacent to the Olympic Stadium. The relighting of the flame at dusk on September 15, 2001, signaled the start of Ignite!, a three-weekend festival staged by the Sydney Olympic Park Authority, as part of its plan to maximize the use of the facilities built for the 2000 Olympics.

The Cauldron, a stainless-steel ring some 10m (33') in diameter and seven tons (15,000lb) in weight, now floats in the air, about 10m above the ground, supported on 24 slender stainless-steel columns. Water cascades through the perforations in the disc and down onto the paved area below. On special occasions, the Cauldron springs back into life with a ring of gas flames and colored under-lighting, conjuring up a look evocative of that now-famous moment during the opening of the Olympics.

Architect Alec Tzannes's design for the Cauldron's new home called for a freestanding structure in an uninterrupted space, with no lighting poles or fixtures set in mounds of earth. This left lighting design team Barry Webb, Iain Clark, and Fiona McVicar of Barry Webb and Associates (BWA) with little choice but to light the Cauldron from below, through portholes set in the pavement. “The lighting system is required not only to work in balance with the brightness of the flames and look exciting with or without the water cascading from the Cauldron, but it must also accommodate members of the public splashing in the water,” explains Clark. This last requirement was eventually to set the limits on the lighting system, as 220mm (8.5") was deemed to be the maximum safe diameter for a glass porthole. The effective aperture was further restricted by the need to bond small metal disks, around 25mm (1") in diameter, onto the surface of the porthole glass, to reduce the risk of slipping.

After considering a wide range of conventional architectural luminaires, the BWA team called in Jonathan Ciddor from Show Technology (Australia's Martin and Clay Paky distributor) to discuss the possibility of using entertainment-type moving-mirror luminaires. They were particularly interested in using the Clay Paky Golden Scan 3, as it not only had the light output and color-changing capabilities they were seeking, but it also had a track record of reliability on previous BWA projects, although never previously underground.

The moving mirror on the Golden Scans offered the possibility of very fine focus adjustment, without the need for a complex mounting system for the fixtures. Additionally, the focal point of the optics was behind the porthole, thus eliminating hot spots on the porthole glass that could cause cracking, or the risk of burn injuries to the water-frolicking public. Maximum light distribution through the portholes called for a 23º beam angle from the Golden Scans, rather than the standard 16º. Show Technology and Clay Paky technical staff tested a variety of lens options before selecting a configuration that was optimal for the project. The final design employs 22 Golden Scan 3s, in two rings: six on the inner and 16 on the outer. Despite the wide range of effects possible with the Golden Scans, they are at present only being used for their color-changing capability, and are currently only programmed for full washes in half a dozen colors.

LIGHT OVER WATER

The Golden Scans are mounted on adjustable brackets, fixed to the ceiling of the 5m-deep (16') circular concrete bunker under the Cauldron. This chamber houses all electrical, gas, water, and control systems for the Cauldron's burners, water cascades, and lighting. It also features a range of ventilation, cooling, environmental monitoring, and alarm systems to ensure that there is a safe, stable operating environment for all equipment, and a breathable atmosphere for visiting maintenance staff.

In assessing the long-term operational requirements of the luminaires, Ciddor identified several possible points of failure in this hostile environment. One concern involved the condensation that would occur at the glass portholes — in particular, how this might impact on operation of the electronics of the Golden Scan 3s. The solution, devised jointly by Ciddor and Con Andrews of lighting contractor Beyond Audio Visual, was to invert the bodies of the luminaires, thus placing the access panel on the underside of the mounted units. A galvanized steel “overcoat” was then fitted to the top of the luminaire body, to deflect any dripping water. The other challenge was to ensure that the failure of any one luminaire could not endanger the operation of the entire system. The solution to this was to feed every luminaire off a separate power circuit, putting each unit on its own optically-isolated control feed, using three 10-way LSC MultiSplit DMX splitter/amplifiers.

Control for the lighting system is Martin Light Jockey 2 software on a Windows/Intel PC, working in conjunction with the freeware LightJockey Scheduler package. In addition to the Light Jockey's DMX512 input and output, outside-world interfaces are via a Martin ADDA, 16-channel, 0-10V analog input card, and a Martin DMX Switchpack that provides six channels of switched mains.

The inputs have been configured to trigger from relay closures to provide synchronization to two external systems. The first is a single “lights-on” sequence triggered from the Olympic Park precinct's C-Bus control system. The remainder are triggered by the show controller PLC from Controltech Engineering which drives the water and flame systems. These inputs can trigger one of five available programmed sequences from the LightJockey. Measures were also taken to avoid the potential mains problems associated with powering-up 22 magnetic ballast 1,200W metal-halide luminaires. Not only have power factor correction capacitors been fitted to the supply circuits for the luminaires, but the LightJockey is also used to control a programmed power-up sequence, via three-pole contactors driven by the DMX Switchpack.

Provision has also been made for remote control of the Cauldron lighting system for public events, such as the Ignite! festival. Within the park area are two DMX control points, each buffered via LSC Isonodes. These are terminated at the main DMX patch field, adjacent to the control racks in the bunker. For the series of concerts staged during Ignite!, the Cauldron was controlled by the Flying Pig Systems Wholehog® II that was also running the stage and park effects lighting.

The Olympic Cauldron is back in business as an attraction in its own right, with the potential to stage spectacular light, flame, and water shows.

Andy Ciddor of The Kilowatt Company has been a practitioner, educator, and writer in the field of production technology for 30 years. He can be reached at aciddor@kilowatt.com.au.