Motion Magic for the Movies

Many of us thrilled to the life-like seagoing atmosphere aboard Russell Crowe’s H.M.S. Surprise in the hit movie Master and Commander.

Little did we know that the action really took place in a water tank.

To a great extent, what made the movie so realistic was the simulated-motion system designed by Bosch Rexroth and its distributor, Hydraulics Controls Inc. (HCI) of Walnut, CA.

The movie was the latest in a string of motion pictures that feature behind-the-scenes collaboration between the hydraulics manufacturer and HCI, including: Men in Black, Jurassic Park, The Perfect Storm, Spider-Man, Volcano, Titanic, Independence Day and True Lies. So it came as no surprise to Mike Rogers, engineering manager of HCI, when Dan Sudick, special effects coordinator at Commander Productions Ltd., Los Angeles, requested HCI’s services in making Master and Commander.

Sudick asked HCI to provide the hydraulic components to power a multi-axis motion platform, or gimbal. The gimbal, in turn, controlled a full-size replica of a 19th century naval frigate that would "sail" in a 6.5-acre water tank with a crew of more than 100 actors and cameramen on board. The replica of the ship, based on the H.M.S. Rose, a floating museum in Bridgeport, CT, was built with painstaking attention to detail: 179 ft long with a mast rising 130 ft above the water, and a design load of 200,000 lbs.

"To my knowledge, this is the largest motion platform of its kind ever used in a motion picture production," says Sudick. "It is approximately 40 ft tall, with a 40-ft base and weighs 60 tons. I asked HCI for their assistance, because our track record with them has been flawless.”

The Design Challenge

To simulate the full range of motion, including the heaving, pitching and rolling of a ship at sea and in battle, the gimbal needed to provide various axes of motion, while constantly being bombarded with hundreds of gallons of water from a wave machine.

Throughout the development process, Rogers consulted with Bosch Rexroth. For example, Paul Stavrou, manager of technology marketing, ran computer simulations on the design using Rexroth's proprietary HYVOS software. The objective: Determine whether or not the gimbal would operate as desired in various load and motion profiles.

As a result of the simulations, Rogers refined his design, noting: “I was only too happy to make the suggested revisions. We were able to use less expensive proportional valves than I had originally specified. It saved our customer money without sacrificing performance.”

The final design called for eight cylinders to control gimbal motion. Four 10-inch bore x 108-inch stroke cylinders addressed the heave axis, lifting the ship up and down. Two 8-inch bore x 38-inch stroke cylinders provided the pitch axis, raising and lowering the bow as needed. Finally, two 12-inch bore x 51-inch stroke cylinders controlled the roll axis, enabling the ship to roll from port to starboard. All the cylinders operated under water, usually under turbulent flow conditions, to simulate the motion of a ship at sea.

In addition, a cable-extension transducer tracked the position of each cylinder. Two 750-hp diesel engines, each driving four Rexroth pumps, powered the cylinders on the gimbal. These systems produced up to 500 gallons per minute at 3,000 psi to bring the gimbal's complex motions to life.

Besides the central hydraulic system, Bosch Rexroth designed and built four custom high-flow manifolds for the project. The heave axis used two manifolds, and the pitch- and-roll axis each employed one manifold. Each of the manifolds was machined to mount a total of six Rexroth 4WRZ25 proportional valves, powered by Rexroth VT11011 analog driver modules. The manifolds also included Sun Hydraulics anti-cavitation valves and relief valve cartridges.

What were the reviews on the performance of this complex hydraulics design? Says Sudick: "Throughout the 22 weeks of filming, the hydraulic system turned in an award-winning performance. Not once during the long 12- to 14-hour days of shooting did the system fail."