Hydraulics reaches the far east
Turning our attention to the other side of the world brings us to Phuket FantaSea, a cultural theme park located at Kamal Bay on Phuket Island, Thailand. This 140-acre theme park comes alive at night by combining the charm and beauty of Thailand and ancient Thai traditions with modern technology and special effects. The result is a stunning theme complex packed with a multitude of activities. The highlight is a Las Vegas-style theatrical show, where state-of-the-art technology and special effects enhance the grace and beauty of Thailand’s myths, mysteries and magic.
This show, Fantasy of the Kingdom, centers around a centuries-old legend of an enchanted kingdom blessed with unsurpassed beauty, bounty, its joyful people, and their young ruler, the Kamala Boy, riding on his heavenly elephant. To help entice visitors into the show, a statue of the Kamal Boy atop the heavenly elephant seems to come to life. The elephant’s tail, head, ears, leg, and trunk all move, as do the boy’s head and right arm. These movements — 13 degrees of motion — all are synchronized with a sound track to give viewers a sampling of the techno-magic awaiting them inside.
The statue is made primarily of fiberglass cast from sculptures of the elephant and boy. Joints and sections that move are made of silicone colored and textured to closely match color and texture of the fiberglass sections. Inside the figures are hydraulic cylinders that produce motion. A programmable logic controller (PLC) mounted in the elephant’s abdomen controls all motion sequences, and critical motions are controlled by electronic servovalve drivers.
The elephant executes seven degrees of motion: head up and down, head left and right, ears out and in, trunk up and down, tail back and forth, and front-left foot up and down (which involves bending upward at the shoulder and downward at the knee). The combined motions of the trunk and leg allow the elephant to “salute” the viewers.
Meanwhile, the boy’s motions encompass head up-down, head left-right, mouth open-close, and two motions for raising the left arm by bending at the shoulder and elbow. Eleven of the 13 motions are accomplished with double-acting hydraulic cylinders actuating on pivot points. None has a bore greater than 2 in., and operating pressure is about 2000 psi. Left-right motion of the boy’s head is accomplished with a rotary actuator. (The rotary actuator is used because the 120° arc of motion would not be practical with a cylinder.)
The articulated statue stands atop a pedestal as part of a display fountain, which is directly over a small basement housing the hydraulic power unit. The platform on which the figure stands pivots 90° clockwise and 90° counter-clockwise from center to provide a clear view to all watching this pre-show. The motion is achieved with a hydraulic motor driving a chain attached to the platform.
Lenz explains, “It would’ve been nice to turn the statue left and right through a rotary actuator mounted right under the center of the platform. But this space near the center of the vertical axis must be used for routing fluid and electrical lines from the stationary HPU and base to the rotating members. Instead, we made a cylindrical extension attached to the underside of the platform that acts as a big sprocket. We then attached a length of roller chain to this extension and drive it with a hydraulic motor. The motor is mounted vertically, so the chain drive runs parallel to the ground. If the statue rotated continuously, we would’ve had to route hydraulic lines through a rotating union. But because it has a total rotation of only about 180°, we were able to accommodate the movement simply by making the hoses long enough and managing the movement of their bending.
“To keep hoses from binding or getting tangled, we bundle them together, place the assembly loosely in a sleeve, and gently bend the assembly into an S curve to provide plenty of slack for movement. We also placed a tray made of UHMW plastic to keep the hose and cable assembly from rubbing against anything that could otherwise cause premature wear of the hose cover.”
Another design challenge was to make the trunk’s movements look natural. One method could have been to mount a cylinder at each pivot point of the trunk frame structure, but this would have been expensive, space restrictions would have made it impractical, and it wasn’t necessary because the natural movement on an elephant’s trunk is for the joints to move in sequence. Another alternative would have been to string a cable through each of the joints and use a cylinder to pull on the cable to move the trunk and have it return by spring force or gravity. This option, however, would have made it difficult to achieve natural movements because motion would have been difficult to control when retracting the cylinder. It also would have been cumbersome to design and build.
Instead, Lenz decided to build a trunk structure with joints linked together so all move simultaneously, but not necessarily at the same rate or even in the same direction. As a result, as the cylinder extends, the trunk gradually curves upward, but the end portion of the trunk curves outward. When the cylinder retracts, the trunk relaxes and moves naturally back toward the ground.
Pneumatics for safety
Lenz explained how it is important to recognize which type of technology is most suitable for an application. For example, inside the theater for the Fantasy of the Kingdom show, his company designed and built what he considers the second-largest stage lift in the world. “The largest stage lift in the world is at Radio City Music Hall in New York. That one is hydraulic. The lift we built is electromechanical, not hydraulic. So ours is the largest electromechanical stage lift in the world. It can handle payloads to 120 tons; it is 50-ft wide, 40-ft deep, and has a maximum vertical lift of 28 ft. We couldn’t use hydraulics because the high water table on the island made it impractical to dig deep pits to house cylinders under the stage.”
Even though it is not powered by hydraulics, the stage lift has a sophisticated triple-redundant safety system that makes extensive use of pneumatics. Lenz continues, "First, we have a pair of Powr-Tube flexible-wall cylinders at each end of the stage that, when pressurized, create an interference fit between the movable stage and massive concrete foundation surrounding it. These cylinders are look like 6-ft sections of fire hose crimped at each end with a steel flange. The relaxed tube is flat, but pressurizing it causes it to expand radially and exert tremendous forces between the stage and foundation. Friction pads mounted between the tubes and foundation make the brakes hold tight.
“Second, four of the eight gearmotors have a Horton air brake mounted between the motor and gearbox. These are spring-applied, pressure-released brakes, so if a power failure occurs, the gearmotors will not turn.
“Third, we use pneumatic cylinders to lock the stage in place when it is in the full-up or full-down position. We built eight sliding I-beams into each side of the stage that fit into pilot holes cast into the foundation. Each I-beam is 4-ft long and slides into and out of its respective pilot hole by way of a pneumatic cylinder. They work just like deadbolts. Limit switches communicate signals to the stage PLC when all cylinders are fully extended or fully retracted. Unless all cylinders are fully retracted, the PLC will not release pressure from the shoe brakes or release the brakes on the gearmotors.”