Custom Submersible Motor Assembly Makes Waves

Empire Magnetics, a supplier of specialty motor products, motion control systems and support services, is often called on to develop custom motion control solutions for unique applications and environments where standard motion control components are simply unsuitable. One of Empire’s custom motor gearbox assemblies has even made its way into show business as an unnoticed yet essential co-star in “O” by Cirque du Soleil at Bellagio in Las Vegas, NV.

In June 1999, the technical team at Cirque du Soleil contacted Empire Magnetics to provide robust, submersible motion control for precise, reliable operation of a motorized, battery powered piano that had to operate in and out of water, show after show, and year after year. Additionally, because the piano must also operate in water with performers, safety precautions demanded that the motor operate at less than 24 V, and provide enough power to move the piano around the stage.

Empire had approximately three weeks to complete the job, from design and fabrication, to testing and operation. Empire engineers provided a Hall effect commutated three phase brushless motor integrated with a cycloidal gearbox. The motor has a special low inductance winding to operate from 24 V dc, and Hall effect switches mounted in the housing to provide commutation information to a brushless-motor drive. The motor directly drives a Sumitomo SM-Cyclo cycloidal gearbox. To make the assembly shorter, the motor shaft and mounting have been adapted to integrate with the gearbox.

The gearbox has only three moving parts: a high-speed input shaft with integrally mounted eccentric cam and roller assembly, cycloidal discs, and a slow-speed output shaft.

The entire assembly is housed in an oil-filled, pressure-compensated stainless steel housing. Pressure compensation is used to prevent oil migration past the shaft seals when the motor is taken in and out of the water. The cable assemblies are sealed to prevent migration of oil or water.

Oil selection was particularly challenging, as the oil must not attack the materials of the motor, windings, wires, Hall transducers, or anything else in the assembly. The oil cannot be toxic. It should be harmless to people in the event of a spill, and should not vaporize at expected operating temperatures. It should also be a reasonable lubricant for gearbox and motor bearings so as to avoid robbing significant power.

The gearbox assembly is integrated into the piano that is the focal point of the show’s finale, where the motors spin in opposite directions, allowing the stage to virtually turn on a dime. The performer controls the motors with a joystick attached to a foot pedal.

Author Information

Rick Halstead is president of Empire Magnetics.

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