What did it cost to animate King Kong with hydraulics? Even with the job completed, Robinson can only estimate.

"But," he told us, "it was only a fraction of the cost of electromechanical animation. You can begin to get some idea from our having Kong ready for the cameras in less than five months, compared to the year-and-one-half estimated for the electromechanical proposal."

"I had told De Laurentiis we probably could do the bare-frame hydraulics and aluminum tube skeleton for around $500,000. Adding two extra arms (for close-up, interior camera shots, see box), and the hydraulic pumps, which were exterior to the studio to avoid noise pickup, and renting cranes to lift the extra arms and erect the big ape, the total possibly went to $800,000 — still several times less than the cost of the electromechanical animation.

"We started with a budged of $1.5 million for all special effects, excluding the animated Kong. Only an auditor's accounting could verify it, but I've been told that we wound up with a budget surplus of about $385,000."

This article was originally published in the April 1977 issue of Hydraulics & Pneumatics. It is reprinted here for its historical and archival value.

How do you animate a 42-foot, 11½-ton hairy ape?

After Dino De Laurentiis gave the go ahead for Glen Robinson and his crew to build a hydraulically animated ape, they set out to create King Kong. Four-and-one-half months later, Kong was erect, on the set, and ready to perform--a bare half hour before filming.

Close up of maze of hose and cylinders in fingers of Kong's 7-foot-span hands.

At director Guillermin's commands, the huge Kong instantly and smoothly raised his hands 55 ft into the air; blinked his eyelids; moved his eyes to "focus" on the object of his gaze; and curled or uncurled his 8-in. diameter fingers. Cylinders moved aluminum plates in his chest to make him "breathe".

Hidden within his hairy figure were hydraulic muscles and their commanding nerves — 140 hydraulic cylinders; 84 remotely-controlled proportional valves (stacked 16 high in his belly); two hydraulic motors to turn his wrists and arms; 150 potentiometers; and 3100 ft of hydraulic hose, with as many feet of remote control electrical wiring.

Jointed aluminum tubular booms served as mounts for hydraulic cylinders in Kong's upper and lower arms, and carried a hose leading to cylinders in Kong's hands.

To operate the extra pair of arms for detail shots, there were: 50 cylinders; 34 proportional valves; two hydraulic pumps and motors each; potentiometers for each cylinder and motor; and hundreds of feet of hydraulic hose and electrical wiring.

Two extra crane-supported arms hold Jessica Lange during filming of scene where Kong curiously explores Dwan's anatomy. Note the hydraulic hose network extending from crane heads into each arm, which required six men to operate the controls. The most complex part of Kong was his hands. They were almost as perfect in movement as human hands. During this scene, Kong was able to use his left forefinger to gently remove Dwan's necklace (and almost her dress!)

For remote control of each animating cylinder and motor, nearby benches were arrayed with 150 manual control boxes and their actuating levers, manned by as many operators as were needed for a particular scene. Each control box included its own potentiometer to sense control lever position, and to electrically transmit it to the remote proportional valve commanding the related hydraulic cylinder or motor. The photos in this box show some of the stages in construction of the giant King Kong.

Stack of three proportional valves such as this one were used to command the animation of King Kong.

Click here to see the theatrical trailer, which shows footage of the electrohydraulic Kong and the electrohydraulic hand that clutches and appears to lift Jessica Lange.

This shot is similar to the one at the beginning of the article, with Jessica Lange being held by the giant electrohydraulic hand. The main difference is that the blue screen has been replaced with footage that makes the hand appear to lift the Dwan character high into the air. Even though Kong’s giant hand is capable of closing into a fist, for safety reasons described in the article mechanical stops in the cylinders limit the amount of inward travel.

 

As in the previous shot, this image shows the hand with moving imagery filling the neutral blue screen in the background, providing the illusion of motion. The fingers’ wide range of motion can be seen by comparing this image with the previous one, where fingers are closed.
The electrohydraulic special effects for King Kong extend far beyond hand and finger movements. Multiple actuators in the face, neck, and arms gave unprecedented realism to give the audience emotional attachment to the Kong character, shown here in one of the last scenes of the movie.