A fourth-dimension roller coaster is a type of steel roller coaster whereby riders are rotated independently of the orientation of the track, generally about a horizontal axis that is perpendicular to the track. The cars do not necessarily need to be fixed to an angle. History John F. Mares, a corporate attorney, invented a fourth-dimension roller coaster concept in 1995 and holds six US patents related to the technology of their spinning seat systems: , , , , & . In this concept, riders control the spinning action themselves. The first fourth dimension roller coaster to be built, X2, which opened at Six Flags Magic Mountain in 2002, was designed and patented by Alan Schilke. In 2007, Intamin launched a variation of the 4th Dimension roller coaster under the name ZacSpin. Design Arrow Dynamics and S&S Worldwide Arrow Dynamics was the first company to produce a fourth dimension roller coaster, lending its name to the ride style. The trains feature seats capable of rotating forward or backward, 360 degrees in a controlled spin. This is achieved by having four rails on the track; two acting as per normal, and two to control the spin of the seats. The two rails that control the spin of the seats, known as "X Rails", vary in height relative to the track, and spin the train using a rack and pinion gear mechanism. The first installation, X², was a prototype and cost Arrow Dynamics and Six Flags itself a lot of money due to technical difficulties and design flaws. In 2002, the park sued Arrow Dynamics, which went into bankruptcy. Since then, Arrow was bought out by S&S Worldwide and became the company's steel coaster division, S&S Arrow. In 2006, a second installation opened at Fuji-Q Highland in Fujiyoshida, Yamanashi Japan under the name Eejanaika. A third installation opened in 2012 at China Dinosaurs Park in China under the name Dinoconda. Intamin ZacSpin first generation The Intamin ZacSpin was developed in response to the Arrow Dynamics fourth-dimension roller coaster. Some of the main differences between the Intamin and Arrow Dynamics/S&S Worldwide versions are the uncontrolled rotation of the seats, which produces a different ride each time, no need for an additional rail, and single cars with two riders back-to-back. Since these single cars don't rotate around the riders but around a common point quite far back behind their backs, this gave rise to complaints