What is in this article?:
- Now playing on Broadway: Fluid Power
- Advantages of hydraulics
Peculiar requirements are commonplace in supplying hydraulic systems for use in Broadway and other legitimate theater productions
Hydraulics usually is called on to generate motions that require high force, rapid movement, and precise positioning. This is true of industrial applications as well as those in the entertainment industry — especially today’s big theme parks. Although these characteristics often are demanded in legitimate (live) theater productions, they do not necessarily play the lead role. Versatility is just as important or perhaps more so because a system must operate successfully even if application parameters change drastically after a system has been installed. The ability to tune — not just fine-tune — operation of an electrohydraulic system may be its most beneficial quality for live theater.
Versatility holds down costs
Ideally, hydraulic systems for legitimate theater should be designed to operate close to capacity. However, such systems often would have to be redesigned because new loads and speeds often exceed those originally specified. These re-engineering costs exceed many times over the cost of building an oversized system to begin with. More importantly, designing and installing a system that ends up being too conservative not only costs the builder money by having to do a system over again, but can also destroy his credibility.
If one of my systems doesn’t get finished on time because I have to reconfigure it, I may never work again in this industry. Once word gets out that your system delays an opening or doesn’t perform as expected, you cannot expect a second chance. I learned this lesson after my first project, — we built a winch that had to lift 12 people at once. Fortunately, the system worked, but if one actor had a sandwich in his pocket, it wouldn’t have. That’s how close to capacity it was designed.
Now, we usually oversize everything 100%. If a design calls for flow of 15 gpm, and I’m not absolutely certain that we’ll need only 15 gpm — or if a colleague thinks we might need more — we size everything for 30 gpm. We always use variable-displacement pumps on our power units, so we’re turning all this extra capacity into heat. It’s well worth the money because even if the system is oversized, it will work right the first time.
In a sense, hydraulics gives you room to be wrong. If you decide on a 3-hp electric motor, and a 3-hp motor doesn’t work, increasing electrical power transmitted to the motor will only burn it out. When you have only three to six weeks to complete a project, and you know you’ll have to make changes down the road, you must have a system that makes implementing changes convenient. That’s what the versatility of hydraulics gives you. If you need more speed out of a hydraulic motor, you can increase flow. If you need more torque, just let the system run at a higher pressure, within reason, of course.
Fear of hydraulics
Many contractors for shows avoid using hydraulics because the thought of all that oil over the heads of live actors is scary. It still scares me because the hydraulic components are not sitting up in their own pristine little world; they’re nested within the scenery. If something blows, the oil isn’t going to be contained. It’s going to go everywhere. The potential for ruining hundreds of thousands of dollars of scenery and costumes seems minor in comparison to getting hot oil on the actors. If this happened, you’d suddenly see contracts written prohibiting the use of hydraulics anywhere near live actors.
The potential liability becomes even greater with shows like Starlight Express. In this 1989 production, actors skated on articulated bridges. One of these bridges pivoted to a position where a portion of it was over the audience. Imagine the liability of oil gushing or even just dripping out of the bridge onto the audience, many of whom would be wearing formal attire
Whether justified or not, this fear of leakage is the main reason some contractors avoid using hydraulics. Instead, they use ballscrews driven by variable-speed DC motors. The preference for electrical connections over hydraulic is another perhaps misguided policy. Electrical cable is thought to be more flexible than hydraulic hose, and it doesn’t leak. But with the wide availability of hose that exceeds current standards for flexibility, hydraulic hose can be easier to work with than electrical cable.
One can understand some people’s reluctance to use hydraulics if they still perceive hydraulic systems plumbed with pipe fittings instead of straight-thread, flat-faced fittings. We don’t use pipe fittings. Period.