Officials at any of The Walt Disney Company subsidiaries are usually quiet when it comes to describing the technology behind new attractions. The reason is simple: Guests marvel at what goes on in these attractions, and revealing the technology behind the magic might somehow take some of the wonder out of the experience.

However, company officials were so impressed with what hundreds of craftspeople, technicians, and engineers were able to accomplish with their newest creation — Expedition Everest at Disney's Animal Kingdom, Lake Buena Vista, Fla. — that they tipped their hand. The highlight of Expedition Everest occurs when guests come face-to-face with the yeti, the most highly engineered Audio Animatronics figure ever created by Walt Disney Imagineers. The yeti stands well over 20-ft tall and, counting all motion axes, weighs in at 20,000 lb. As guests zoom past the yeti in a roller coaster train, it shows off 19 axes of lifelike motion by lunging at the train and swiping at it with an arm more than 10-ft long.

The yeti is one of the stars of Walt Disney World's newest permanent attraction, but there's much more to Expedition Everest than the yeti. There's a scaled-down Himalayan mountain range, a mythical village inspired by the architecture of Nepal, and, of course, a roller coaster.

As the story goes

As guests enter the Expedition Everest site, they work their way through a maze of authentic props to give the impression they have entered a Himalayan village. During this initial storytelling portion (everything in the attraction is about storytelling), guests learn that they will embark on a tour through the mountains aboard an old train that formerly hauled tea and is still powered by a steam locomotive.

Guests also catch frequent glimpses of Everest towering in the distance. The structure is nearly 200 ft tall, but appears much taller through forced perspective. Forced perspective involves altering the scale at which objects are constructed and painting shadows that create a false sense of depth.

However, guests are repeatedly shown references to the legendary Abominable Snowman — or the yeti, as it is referred to in Himalayan custom. These references become more intense as guests work their way closer to where they will board the roller coaster.

All aboard

As they approach a loading platform, guests see and hear coaster trains approaching and departing. A train departs as often as once a minute with as many as 34 passengers on each. The coasters are adorned with features that make them appear to be old rusty trains. They have a steel framework with outer bodies made of fiberglass for a combination that is light weight, strong, and durable.

To add realism to the scene, steam is routed to nozzles mounted under the loading platform. This makes it easy to see and hear the steam, but keeps it a safe distance from guests and attraction personnel. A blast of steam is released every time a train stops at the loading platform, giving the impression that the train is, indeed, powered by a locomotive. Steam is again released — and a steam whistle sounds — once the train has been loaded and begins its departure.

It's a switch

Upon departure, the train ascends the attraction's first hill. After climbing a second hill, 112-ft high, the coaster enters a snowy canyon. Something appears seriously wrong. Huge footprints in the "snow" and a distant roar signal that the guests have infringed on the yeti's space. Worse yet, the track ahead is broken and twisted — with nowhere to go except off the track and over a steep cliff!

Lacking any other recourse, the train comes to a halt, then backs up. But instead of heading back into the loading area, it crosses over a switch track that diverts it — backwards — to an alternate route. The coaster continues backward and up through a spiral and eventually stops at the top of an incline. After a brief pause, it rolls forward down the hill, then crosses over another switch track that sends it down an 80-ft drop. The coaster reaches speeds up to 50 mph.

Pneumatics in action

Both switches are thrown by pneumatic linear actuators. But unlike conventional railroad switches, which actuate laterally, these switches rotate on their longitudinal axis, thereby keeping the mechanisms hidden from sight.

Each switch contains four actuators mounted perpendicular to the axis — a pair at the front of the switch and a pair at the rear. One actuator of each pair pushes the switch clockwise while the other pulls it. This setup conserves more space than using one or two large actuators for each switch and more evenly distributes loads. However, these switches are no lightweights; each weighs 20,000 lb. This may seem like overkill, but each switch must support a heavy roller coaster train carrying as many as 34 people.

Once the train has passed completely over the switch, controls unlock a mechanical linkage that holds the switch in place. Controls then command the switch to rotate 180°, then the mechanical lock is reset. The entire sequence occurs in about six seconds. Adding to the challenge is controlling the rotational motion of the switches.

Pneumatic actuators usually shift discretely — they shift from one extreme to the other in an instant. In this case, though, the actuators move through an acceleration ramp, to constant speed, then

through a deceleration ramp. This is done to minimize shock to the system, which extends life. It also reduces noise.