Cartier - The Rotonde de Cartier Astrotourbillon watch
This spectacular creative and highly technical movement is the fruit of five years of development led by the Cartier Manufacture in La Chaux-de-Fonds.
The 9451 MC movement incorporates a tourbillon carriage containing the various organs of the escapement and sprung balance.
As in a classic tourbillon, the carriage is driven by the third wheel of the gear train. Similarly, the pinion of the escapement wheel rotates around a fixed seconds-wheel (the fourth wheel of the gear train) in order to drive the escapement.
However, this spectacular tourbillon, christened the Astrotourbillon movement, also incorporates several other features that make it truly unique.
First of all, the carriage has a special rotational axis, for it is positioned at the centre of the movement. This naturally requires a totally different gear-train design, from the two barrels of the movement through to the display of the minutes and hours.
Another feature, responsible for the striking visual effect created by the Astrotourbillon movement, is that the balance staff and escapement-wheel staff are not on the same rotational axis as the carriage. They are located to one side of the carriage, in linear alignment with its rotational axis. Lastly, the tourbillon carriage is positioned "above" the movement between two dials, rather than being directly integrated into the movement as with classic tourbillons.
This construction is highly unusual for a central tourbillon and has both aesthetic and technical consequences. Visually, the elongated carriage makes a complete revolution around the entire surface of the dial in one minute. The off-centred balance bridge, shaped like an arrow, indicates the seconds. Technically, in order to ensure the equilibrium of the carriage, it was necessary to incorporate a platinum counterweight on the opposite side of the carriage, hidden under the central dial. Furthermore, the weight of the carriage had to be limited (0.39 g for the entire carriage, excluding the counterweight) in order to control its inertia during rotation, hence the choice of titanium for its construction.
Cartier has selected the contemporary elegance of the extra-large Rotonde de Cartier watch to house this movement. Its white- or pink-gold case, 47 mm diameter, large horn gap, and decorative screws all enhance the hypnotic effect of this truly elegant watch.
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