Motion simulators are classified based on whether the occupant controls the vehicle or is a passive rider. Flight simulators for pilot training are an example of occupant-controlled motion simulators. Other examples include driving simulators and hydraulic arcade cabinets for racing games. Passive ride simulators are found in theme parks where an entire theater system, with a projection screen, sits in front of riders.
Motion platforms for aircraft simulators are at the high end of cost and capability, along with some expensive amusement park rides that use a simulator-type motion base. Arcade amusement devices are in the middle price range, while motion platforms for home use are low-cost but less capable than higher-level devices.
One of the earliest motion platforms, the Sanders Teacher, was created in 1910. This model aircraft was connected to the ground by a universal joint, allowing the pilot in training to use control surfaces to move the model in the three rotational degrees of freedom: pitch, roll, and yaw. A significant advance occurred in 1929 with Edwin Link's patent for the "Link Trainer", which used organ-type bellows to provide movement in pitch, roll, and yaw.
In 1958, a flight simulator for the Comet 4 aircraft utilized a three-degrees-of-freedom hydraulic system. Today, simulator motion platforms often use 6 jacks, known as "Hexapods", providing all six degrees-of-freedom: pitch, roll, yaw, heave (up and down), sway (sideways), and surge (longitudinal). These 6 DOF motions, combined with OTW imagery, are powerful cues used in flight simulation, driving simulation, amusement rides, and small home-based simulators.
In the 1980s, hydraulic motion simulator arcade cabinets became a trend, sparked by Sega's "taikan" games. Sega's first game to use a motion simulator cabinet was Space Tactics (1981). Yu Suzuki's team at Sega developed Hang-On (1985), a racing video game where players move a motorbike replica. This was followed by hydraulic motion simulator cockpit cabinets for games like Space Harrier (1985), Out Run (1986), After Burner (1987), and G-LOC: Air Battle (1990). Sega's R360 (1990) was a sophisticated motion simulator cabinet that simulated full 360-degree aircraft rotation.
The perception of our body and surroundings is influenced by how the brain interprets signals from sensory systems such as sight, sound, balance, and touch. Postural stability is maintained through vestibular reflexes acting on the neck and limbs, controlled by three classes of sensory input: proprioceptors, the vestibular system, and visual input.
Proprioceptors are receptors in muscles, tendons, joints, and the gut that send signals to the brain about the body's position and accelerations. The vestibular system, located in the inner ear, consists of semicircular canals and otoliths. Rotational accelerations in pitch, roll, and yaw are sensed by fluid movement in the semicircular canals, while linear accelerations in heave, sway, and surge are sensed by otoliths. Visual input from the eye relays information about the craft's position, velocity, and altitude relative to objects in the OTW visual scene.
In simulator motion platforms, an initial acceleration is produced, then the platform is reset to a neutral position at a rate below the human motion threshold. This "acceleration onset cueing" is crucial for simulating how humans feel motions in the real world.
It is physically impossible for most existing systems to correctly simulate large-scale motion within the limited space of a simulator. The standard approach is to simulate cues of initial acceleration as closely as possible. Since the human vestibular system re-centers itself during steady motions, washout filters are used to suppress unnecessary low-frequency signals while returning the simulator to a neutral position at accelerations below the threshold of human perception. This allows the system to remain within its physical limits while providing realistic cues for human perception.
Three common types of washout filters are classical, adaptive, and optimal. The classical washout filter uses linear low-pass and high-pass filters. The adaptive washout filter, developed at NASA Langley, uses a self-tuning mechanism to minimize an objective function. The optimal washout filter incorporates models for the vestibular system to optimize the human's perception of motion.
While washout filters allow for the simulation of a wider range of conditions, there are limitations. For instance, in rapid maneuvers like those in aerial combat, there may not be enough time for a washout filter to return the motion system to its equilibrium, leading to the system quickly hitting its range limits. Filters can also introduce false cues, such as motion in the opposite direction to the aircraft or unexpected motion.
Adverse effects, known as simulator sickness, can occur when sensory cues from visual, vestibular, and proprioceptive inputs do not correlate. Symptoms can include feelings of warmth, sweating, headache, drowsiness, and difficulty focusing. Factors contributing to simulator sickness include individual susceptibility, flight hours, distorted scene content, longer simulation length, and delays or mismatches between visual and motion systems.
This article is based solely on the supplied corpus. No external sources were consulted; claims that could not be substantiated against the corpus were omitted under the drop-the-claim rule.
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