Assume for the moment that you are the engineering manager for a company that will design and build positioners for products weighing thousands of pounds. Moreover, the positioning will require rapidly changing angles with some lateral movement. Such operation is similar to that used in motion platforms, Figure 1. These units are purchased by entertainment firms dedicated to building small action theaters. These may simulate a run-away mine car traveling underground at fantastic speeds, or a trip through space avoiding unfriendly space cadets, or other thrill rides. Some move the audience up, down, and tilt. More complex units move up, down, sideways, and tilt. All the moves must be coordinated with an image projected on a large screen. If it isn’t, viewers get upset real fast. Many theaters will have multiple modules with a single screen.

Similar motion platforms move interactive simulators for training truck drivers. Each simulator contains a truck cab mounted on a motion platform. The driver views typical scenes he would encounter on the road while feeling the associated motion. Again, the motions he sees and feels are coordinated.

As might be expected, the motions in the entertainment simulators are more severe than for training applications, which must relate to reality, rather than provide thrills.

Interestingly, many of these platforms for entertainment are sold to the companies in the Pacific Rim, because there is little usable real estate. Rather than build new motion theaters, they convert old movie theaters to ones that move the audience while they watch visual and hear audio stimuli.

Platform designs

Typically two basic designs are used for these applications. One has four axes of motion — called four degrees of freedom (DOF), Figure 2. This can move each side independently up and down, thus tilting as well as moving the whole platform up and down. The other design has six axes, Figure 3. This design offers the four axes plus the ability to move the platform in yaw and sway directions, Figure 4.

Quantifying requirements

As with any engineering assignment, factors must be quantified. The factors involved in these motion platforms include load weight, centers of gravity, motion profiles, and enclosure dimensions. Load weight establishes the minimum and maximum weights the motion platform will move, both empty and fully loaded and weights in between.

Centers of gravity (CG) include all possible loads. For example, the CG must be established for one person in the module, two in each possible seating configuration, etc.

Motion profile is often difficult to establish, especially if this type of device is new to the ride manufacturer. Frequently, the directions are vague, such as, “Let’s make the audience feel as if they are in an aerobatic aircraft during an air show.” To establish the acceleration and deceleration rates for all directions, engineers often put sensors on something that approximates the desired thrill. Then, using the values obtained empirically, they write a motion profile that is synchronized with the visual effects and emulates the measured quantities. (Programming is discussed later.)

Dimensions of the load and the enclosure must be established. It may be necessary to restrict the maximum movements to prevent the top of the moving unit from poking holes in the surrounding enclosure.

Safety and reliability

Without doubt, safety and reliability, including long-term maintenance costs, are among the most important engineering considerations. People must not be endangered even if a component should fail or power is lost, or both at the same time. Should an unsafe situation occur, or should an operator believe a dangerous situation might arise, the system must enable all personnel to leave the unit in an orderly manner.

In addition to the safety restrictions, reliability takes on added values in the entertainment industry than even in many competitive industrial installations. From an economic standpoint, if a ride or other attraction is out of commission, it has lost irreplaceable revenue for as long as it is inoperable. No amount of overtime will make up for the lost revenue. Moreover, typical thrill rides operate continuously over 12 hours per day, 7 days per week.

Equipment selection

Based on equipment capabilities and customer preferences, two types of linear actuators have emerged for these motion platforms. For payloads over 10,000 lb, hydraulic actuators are often the best choice. These payloads are typically encountered in flight simulators for large aircraft such as the B-747s. Large simulators usually include a full cockpit, computer for controlling the entire system, audio-visual units, and room for three people.

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