In February 1976, producer Dino De Laurentiis was one month into the shooting schedule for King Kong when the engineering firm bidding to build the giant ape informed him that, using an electromechanical system, would require five months to build a small prototype model, and an additional year to scale it up to its final size. And De Laurentiis had to release the film in December, 1976, less than 11 months in the future!

Glen Robinson, MGM's chief of special effects on loan to De Laurentiis came up with the answer. "We can do it in four months. But you'll have to let me do it my way — with hydraulics."

With an estimated cost of $500,000, De Laurentiis gave the go ahead. Robinson, his special effects foreman Joe Day, layout foreman Jimmy Thomson, and a host of welders and hydraulic mechanics were on their own.

No time for circuit diagrams

Considering the tight time schedule they faced, there was no time for designing the circuits first on paper. Based on anatomical sketches by Italian sculptor-engineer-designer Carlo Rambaldi, King Kong's hydraulic systems were breadboarded directly on the floor of a cleared section of MGM's construction shop.

"If we had relied on engineering drawings, we really would have been in a bind because we had to change the size of Kong three times," Robinson said.

Breadboarding was well on the way for a 35-ft ape when it was discovered that leading lady Jessica Lange, who plays Dwan, could not snuggle safely in the palm of a 6-ft, 2-in. hand. The hand was reworked to a span of 6 ft, 10 in., and in proportioning, King Kong grew first to 48 ft, then shrank to 42 ft.

With no engineering drawings, the practical experience and inventiveness of Robinson and his crew were of prime importance. Because there was no time to order custom cylinders, they used standard cylinders, tested them in assembly, and then improvised if something didn't work right.

For example, there was danger at one point that the cylinders that animate King Kong's hand might over stroke and cause the ape's fingers to crush his leading lady in his palm. To overcome this problem, they incorporated positive stops into each cylinder that shortened the stroke of each finger cylinder and stopped piston travel at a precisely measured point. They could have used conventional external control valves to limit piston travel, but that would have meant adding equipment that might fail— something the leading lady wouldn't like!

The stops were simple, failsafe, and quickly made in the machine shop. They machined a brass cylindrical "plug" to fit the ID of the ¾-in. bore by 2-in. stroke finger cylinders. The plug was drilled with a center hole through which the piston rod passed. Axial holes provided free flow of fluid inside, Figure 1.

Each plug was then cut to the exact length to accommodate various piston strokes. When installed in the cylinder, there was no way the piston could travel beyond the positive stop.

Success of the design was demonstrated during an early set-up scene with stunt woman Sunny Woods substituting for Jessica Lange. As Kong's huge arm lifter her into the air, a ¼-in. wrist cable failed. The hand suddenly drooped limply from the wrist, swinging her abruptly from a vertical to a horizontal position. But the stops held the fingers in position, neither crushing her, nor permitting her to fall.

Proportional valves control motion

Cylinders in Kong's hand varied in size from a ¾-in. bore by 2-in. stroke for his fingers, to those with 4-in. bores and 3-ft strokes to flex his 4½-ft diameter, 20-ft-long arms. Remotely controlling these cylinders was to present an equally serious challenge.

Whatever made Glen Robinson, who is chief of special effects in MGM Studios in Culver City, think that he could do what a high-priced mechanical engineering firm had said would take three times as long and much more money to accomplish?

The first thought was to put a special effects man in an ape suit (to be used for some location shots) and outfit him with potentiometers that would be wired to proportional valves controlling the big ape's cylinders. As the actor would move inside the suit, the big Kong would duplicate his movements exactly.

But suppose that while Jessica Lange was in the big hand, the man in the suit sneezed and flung his hand up toward his nose? "We could just imagine the big ape doing the same," said Robinson, "sending the female star flying over his shoulder and into the rafters of the stage!"

They then decided to use manual remote control boxes, one for each cylinder, manned by carefully rehearsed operators. However, there were still problems.

Applying a variable electrical input signal to a proportional control valve controls only cylinder speed, not its final position. In addition, the 30% deadband in the standard proportional control valves they were using caused a delay before the valve spool shifted far enough to actuate the cylinder. This delay meant that the ape would not respond quickly enough when director John Guillermin called for a certain action, and the scene would be ruined.

Master special effects man puts life in King Kong

"After forty or so years of using hydraulics for all kinds of crazy special effects, you can get a pretty good feel for what you can do," Robinson said. "At MGM, we began using hydraulics back in 1934, when we filmed Broadway Melody."
 

Among the jobs he's done hydraulically was that of making it possible for city-bred extras to sweep the backbreaking oars of Roman slave galleon.

"The Roman Empire could have ruled the seas if they'd had what we cooked up in filming Ben Hur - the first slave galleons ever rowed with hydraulic assists on every oar, and hydraulics keeping the oars sweeping in perfect unison!" laughs Robinson.

In the photo, Robinson holds a jointed frame for massive Kong finger, and indicates location of using actuating hydraulic cylinder. Cylinders on the desk show different sizes needed for various parts of Kong's anatomy.

Editor's Note: As this article was being written, we learned that the special effects in King Kong and Logan's Run (which was also shot at MGM) were voted Special Acheivement Awards by the Academy of Motion Picture Arts and Sciences. This makes Robinson eligible for his third Oscar. He previously won for special effects in Hindenburg and Earthquake.