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The following article appeared in the July 2007 issue of Power Transmission Engineering. Empire Magnetics’ Gearbox Takes Center Ring at Cirque du SoleilEmpire Magnetics, a supplier of specialty motor products, motion control systems and support services, found its custom motor gearbox assemblies—literally—in the spotlight as an unnoticed yet essential co-star in “O” by Cirque du Soleil at Bellagio in Las Vegas, Nevada.
In June of 1999, the technical team at Cirque du Soleil contacted Empire because they needed a robust, submersible motion control solution to provide precise, reliable operation of a motorized, battery-powered piano that had to operate in and out of water, show after show, year after year, says Richard Halstead, president of Empire. The piano must also operate in water with performers, so safety precautions demanded that the motor operate at less than 24 volts, while still providing enough power to move the piano around the stage. The team at Cirque du Soleil was under a time crunch and gave Empire approximately three weeks to complete the job, from design and fabrication, to testing and operation. The solution provided by Empire’s engineers consists of a hall-effect commutated, three-phase, brushless motor integrated with a cycloidal gearbox.
The gearbox assembly is integrated into the piano that is the focal point of the show’s finale, which features a tank-style control system where the motors spin in opposite directions, allowing it virtually to turn on a dime. The performer controls the motors with a joystick attached to a foot pedal. A three-phase brushless motor includes a special low-inductance winding to operate from 24 volts DC. This motor has hall-effect switches mounted to provide commutation information to a brushless motor drive and is directly driving a Sumitomo cycloidal gearbox. To make the assembly shorter, Empire adapted the motor shaft and mounting to directly integrate with the gearbox. The whole assembly is contained in an oil-filled, pressure compensated housing. The cable assemblies are sealed to prevent migration of oil or water.
Halstead says selection of the oil is particularly difficult, as the oil cannot attack the materials of the motor, winding, wires, hall effects, or anything else in the assembly. The oil should not be toxic or vaporize at expected operating temperatures. The engineers mandated that the oil act as a reasonable lubricant for gearbox and motor bearings, not robbing the motor of significant power when it’s turning. In the event of a spill, the oil needs to be harmless. Empire used pressure compensation to prevent oil migration past the shaft seals when the motor is taken into and out of the water. “The entire assembly is housed in an oil-filled, pressure-compensated, stainless steel housing, and has been providing robust, reliable operation for more than seven years,” says Halstead. “We’re just now having an opportunity to do some maintenance work on the original units, and I fully expect the rebuilt units to outlast the show,” he says. For more information: |     | ||||
