There's no business like...

Through the years, I've been fortunate enough to sometimes write and edit article dealing with the entertainment industry. These usually involved thrill rides at amusement parks but also included special effects used in movies and in live theater. Developing these articles generally turns up much more information than space allows to print or that deviates from the magazine's focus of system design.

One article I remember in particular involved an interview with Dan Hoffman, of Showtech, Inc., I learned how he sometimes has to overcome directors' fears or negative perceptions of hydraulics. Dan said this problem usually is overcome once a director discovers that hydraulics was instrumental in the success of other impressive effects. For example, in a production of Peter and the Wolf, Showtech was called on to supply a mechanism that would whisk an actor ten feet off the ground to the top of a tree in about a second with rigging not visible to the audience.

Dan housed a hydraulic power unit and cylinder inside the tree trunk and connected a block-and-tackle assembly to the cylinder rod to gain mechanical advantage. The block-and-tackle arrangement multiplied the stroke of the cylinder but divided its force by an equal factor. This meant hydraulics was the only choice for generating the high force and rapid linear motion needed. A cable on the output end of the block-and-tackle assembly ran inside a low hanging tree branch containing a track. Hooking the end of this cable to a harness on the actor and activating the hydromechanical system gave the impression that the actor lept ten feet from a standing position without any visible cables.

Another problem is how financially risky show business can be for those who are not involved directly. Dan said that in legitimate theater, a contractor like Showtech often can win or lose a bid based on a prep charge. A prep charge is the fixed cost a contractor charges a production company to complete the project at hand. The rest of the money comes from the lease agreement between the contractor and production company. What makes the financial picture so risky is that the contractor has to predict how well a show will do when figuring fixed and contract charges. If he thinks a show will do well -- and, therefore, run for a long time -- he can recover his investment just on the lease agreement and not even quote a prep charge. However, if he thinks a show may close after only a brief run, he will tend to quote a high prep charge because a short lease term will not cover his investment.

What complicates matters even more is competition. If a competitor thinks a show will do well but you don't, you'll likely lose the contract because of your higher prep charge. So trying to win a contract tends to keep your prep charge low, but minimizing risk tends to keep it high. But I guess that's show business.

Hyped up over hybrids

Seems like everything is hybrid these days. My dad had a degree in agriculture from Michigan state, and I remember him telling me about how crops were bred to produce hybrid species that were highly resistant to certain diseases, drought, and other conditions — and that was more than 40 years ago.

Ever since the introduction of hybrid cars, we see the word hybrid popping up everywhere. A news release arrived awhile back describing a new hybrid excavator from Doosan Infracore, Atlanta, scheduled for launch in North America in 2012.

Why is this excavator a hybrid? The release explained that the excavator “will be equipped with a diesel engine, electric swing motor, electric converter, and an ultra-capacitor that will store excess energy during turning and light-duty operations. The reserve electricity will then be used to assist the power of the engine during heavier work; allowing the engine to maintain low revolutions and high efficiency combustion during acceleration.”

Now I’m not surprised that Doosan is replacing the conventional hydraulic swing drive with an electric drive. Hydraulic gear motors are normally used for this function. And although gear motors are powerful, reliable, inexpensive, and extremely compact, they’re not especially efficient. Plus, the rotary output of a hydraulic motor can easily be accomplished with an electric motor — even if the electric package must be larger and heavier. So it stands to reason that if efficiency is your primary goal, you’d consider using an electric motor for the swing drive.

However, Doosan could probably save all that trouble by using a moreefficient bent-axis piston motor instead of the gear motor and use an accumulator instead of the “ultra capacitor” for energy storage. Plus, the hydraulic solution would eliminate the likelihood of overheating the motor and avoid the potential dangers of electricity. After all, excavators are often used near water and out in the rain.

But what I found more puzzling was that Doosan made no mention of using a hydraulic fan drive to cool the excavator’s diesel engine. Hydraulic fan drives can substantially improve fuel efficiency and reduce emissions of diesel engines. How substantial? According to Gary Gotting, of High Country Tek, a manufacturer of electronic controls (including those for hydraulic fan drives), testing has shown that simply replacing a vehicle’s conventional belt-driven fan with a hydraulic fan drive can cut fuel consumption by 14.5%.

For the record, I contacted Doosan to find out what type of drive this machine will use for its cooling system. I was told it uses a conventional belt driven fan drive. Therefore, if Doosan’s goal is to produce the “greenest” excavator on the market, I think they’re missing out if they don’t investigate the virtues of hydraulic fan drives. These fuel savers have been popping up in all kinds of off-highway equipment. They’re just not getting all the hype of hybrid electric drives.