4th Dimension roller coaster

A 4th 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 the 4th Dimension roller coaster concept in 1995 and holds six US patents related to the technology of their spinning seat systems: , , , , & . The first 4th 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 4th 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 1st generation.
The Intamin "ZacSpin" was developed in response to the Arrow Dynamics 4th 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 2 riders back-to-back. But 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 of rider discomfort. Another notable difference is the absence of any lateral movements, causing some enthusiasts to not consider the rides 4th dimension roller coasters due to the fact that all movement is restricted to a 2 dimensional plane.
"Kirnu" at Linnanmäki in Helsinki, Finland, opened for the 2007 season and was the first of its kind. Later that year "Inferno" opened at Terra Mitica in Spain with an identical compact layout. In 2009, "Insane" opened at Gröna Lund with a different track layout. In 2011, the first "ZacSpin" in the United States opened at Six Flags Magic Mountain as "", and was themed to the DC Comics superhero of the same name. It features the same layout as "Insane".
S&S Free Spin.
In late 2012, S&S Worldwide unveiled a new concept called Free Spin which features a similar ride to Intamin ZacSpin. Each vehicle features two seating rows, and each row rotates independently. Because the axis of rotation is at the center of mass of each guest, rider comfort is significantly improved. Like with ZacSpin, Seats spin freely, but during several track sections a system of magnets forces a controlled inversion. The first installation of a 4D Free Spin was at Six Flags Fiesta Texas in 2015.
Intamin ZacSpin 2nd generation.
In 2016, Intamin announced an updated version that like Free Spin also features a vehicle with two seating rows rotating independently, and an axis of rotation at the center of mass of each guest to improve rider comfort.
Inversion ambiguity.
There is considerable debate within the roller coaster community as to whether or not the spinning of these coasters qualifies as an inversion for the purpose of records. Guinness World Records gave "Eejanaika" the record with 14 inversions. However, other more coaster-specific record bodies such as the Roller Coaster Database do not recognize this claim and instead count only "track" inversions, which gives the record of 14 to The Smiler.