Whether you’re into ballet or hip-hop, the staging and special effects now play a major role in performances at many modern theaters and arenas. Behind the scenes, much of the action is thanks to state-of-the-art hydraulic drives.

Bosch Rexroth, headquartered in Lohr am Main, Germany, and with U.S. operations based in Charlotte, N.C., has a group of engineers and technicians dedicated just to stage technology. For more than three decades, the company has supplied leading-edge, easy-to-operate systems for venues ranging from small theaters to large performing-arts centers. Projects vary from quick modernization during short holiday shutdowns to extensive overhauls of all stage machinery.

Stage motion systems usually rely on a combination of hydraulic, electromechanical, and hybrid drives, but the high-power density and compact footprint of hydraulics often makes it the go-to solution when moving large loads or during space-constrained retrofits. Today’s advanced electronic controls permit quick dynamic movements and high operating speeds. And because hydraulic power sources can be installed remotely from the actuators, this ensures extremely quiet movements while preventing heat generation near the stage.

Stage subsystems

The drives are used in mechanisms and machinery above and below stage, including movable floors, platform lifts, and even special set decorations. Hydraulic drives are also routinely used in equipment like lighting hoists and portal bridges.

For example, when a scene changes, powered hoists above the stage ensure that backdrops and other settings are placed precisely where needed or quickly removed. They are often installed as an alternative to manual counterlines during renovation and new construction projects.

Hydraulic cylinders in these applications can reach considerable lengths. Rexroth has installed drives with a lift capacity of 14 m, but even greater heights are possible. If required lifting heights or other conditions rule out a linear drive, hydraulic rotary drives are an excellent alternative.

Hydraulic cylinders operate completely jerk-free across a wide range of speeds. Even when fully loaded, speeds of up to 1.8 m/sec are not unusual and, thanks to high power density, the drives are extremely compact. For instance, they can be mounted at axis intervals of 200 mm on a stage wall to replace conventional manual counterweight systems, and additional space for winches is unnecessary.

In the often-tight confines below stage, hydraulics’ compactness and high force capability offer designers an advantage, as they’re considerably smaller than equivalent electromechanical drives. For example, an orchestra is seated in a pit for opera or ballet performances but needs to be onstage for a concert. Hydraulic drives can move orchestra rostrums to the exact height a specific performance demands.

The same holds for stage podiums and platforms. Powerful hydraulic drives quickly move these structures, some weighing tons. Moreover, highly dynamic movements are both smooth and silent. This is particularly beneficial for equipment like stage lifts and elevators. Independent electrohydraulic control of individual actuators lets operators position various sections at different heights or even tilt them at an angle. Likewise, many performances quickly change scenes by rotating sets mounted on a turntable. Hydraulic drives provide the power to move heavy sets without jolts that could topple the displays.

Technical considerations

Ensuring that all motion-control drives run as intended requires sophisticated controls. Rexroth’s SYB 3.0 stage-control system is engineered specifically for the control and automation of stage machinery, and is reportedly easy to program and operate. The systems’ modular design handles electrohydraulic and electromechanical drives, giving users the flexibility to tailor stage movements to the exact demands of set designers and theater directors.

High bandwidth ensures real-time communication with all drives for precise synchronization and optimally coordinated motion sequences. The software includes integrated 3D simulation tools, and several operators can simultaneously program the same or different performances — features that promote workflow efficiency. And the controls are designed to easily allow for future expansion, modernization, or alteration of the drives.

SYB 3.0 controls also have a collision “assistant” that warns of conflicts before they happen and helps operators ensure safe movements. In fact, safety is a prime concern when engineering stage equipment. It is now customary practice in many localities to operate stage safety devices hydraulically, or by combining an electric drive with a hydraulic brake — because these designs most reliably comply with technical safety requirements.

For instance, should a fire ever break out, active fire-safety devices like smoke vents keep pressure from building inside the stage house and let smoke and toxic gases escape. Hydraulic cylinders that operate independent from the main electricity supply are used with redundant safety circuits to ensure simple operation and positive response.

Like most any operation today, opera houses, theaters, and convention centers -- large and small -- face budget constraints, so energy costs are a prime concern. Rexroth has responded with a range of options that include not only efficiency-optimized components, but entire systems with interactive feedback that minimize power consumption. One example is speed-controlled pump drives that only deliver the required pressure and flow when operations demand, and otherwise slow or completely stop.  

The company also offers systems that make it possible to recycle the braking energy in the form of hydraulic pressure – for instance, when lowering a podium. It’s intensified, stored in accumulators, and fed back into the circuit as needed. Thus, the pump and power unit have to generate less flow and pressure, which ultimately saves electrical energy and lowers operating costs.

Applications

Rexroth engineers have designed dozens of stage systems worldwide — examples include the China National Grand Theater in Beijing, Oslo Opera House, and Vienna’s Burgtheater, just to name a few. For instance, the famed Bolshoi Theater in Moscow was upgraded with more than 600 hydraulic and electrical drives as well as the stage control system. Built in 1825 and now a World Heritage site, the external building dimensions had to remain unchanged during renovation.

It includes a stage pit more than 20 m deep with seven large stage platforms. Each platform has two levels and is 22 m long, 3 m wide, and 10 m high. They each weigh approximately 70 tons.

Hydraulic drives move the units smoothly up and down over a distance of 16 m at speeds up to 0.7 m/sec. And operation is so quiet that none of this can be heard in the auditorium: The hydraulic power unit is mounted remotely away from the platforms, in the theater basement.

The space-saving hydraulic drives were quick to install, provide low energy costs, minimize downtime, require little maintenance, and can be easily upgraded.

Information for this story provided by Bosch Rexroth. For more details on the company’s stage technology offerings, visit www.boschrexroth.com/stage-technology.