====== Micro-rotor ======
{{wst>image_cl|Universal|100 Werkansicht|Movement [[Universal 100]]\\ with **micro-rotor**}}

A **micro-rotor** (also called **microrotor**, **microtor**, and **planetary rotor**) is a compact [[automatic winding]] [[rotor]].

===== Overview =====
Compact [[weight segment]] of an [[automatic]] watch, which can be well integrated into the movement because of its smaller diameter. So the full case height can be exploited. The other competing principle is called the [[central rotor]].

One challenge for micro-rotor movements is the limited amount of power they can generate. The typical solution is to use a more complex bi-directional winding system along with a heavier rotor. Even so, micro-rotor movements are notorious for not fully winding the mainspring without quite a lot of motion.

Today, many brands produce micro-rotor automatic movements, though it is not a dominant design. [[Vaucher Manufacture Fleurier]] are the largest producers, supplying [[Parmigiani Fleurier]], [[Chopard]], and others. [[Patek Philippe]] and [[Piaget]] also have popular micro-rotor movements.

===== History =====
The micro-rotor movement first appeared in [[1958]] with simultaneous announcements of unrelated projects at [[Büren]] and [[Universal Geneve]]. Over time, both companies claimed earlier dates, with Büren claiming a [[1957]] introduction in a [[1965]] advertisement and Universal dating theirs to [[1953]] just a few years later. Contemporary coverage clearly dates the introduction of both movements to [[1958]], however.

At [[Büren]], Chief Design Engineer Hans Kocher championed the concept. He opted for the term, **Planetary**, to describe his micro-rotor movement, since the small rotor reminded him of a planetary gear. The Büren calibre was released as the "Super Slender", even though it was about the same height as competing movements at 4.15 mm. In [[1960]], Büren added a quick date change and corrector to this movement.

At the same time, [[Universal Geneve]] was developing a similar technology and trademarked the term **Microtor** to describe it. Universal's movement was unable to beat Büren with their 4.2 mm [[Universal 1-69|Cal. 1-69]].

[[Piaget]] was another early micro-rotor pioneer, beating both with their 2.3 mm thick [[Piaget 12P|Cal. 12P]] in [[1959]]. It used a solid gold weight segment to improve winding efficiency and had 30 functional jewels. This was celebrated at the [[1960]] [[Basel Fair]] as the thinnest automatic movement in the thinnest automatic watch, Ref. 12444, in the world.

The second generation of micro-rotor movements began in [[1962]] with but Büren [[Intramatic]] line. It was just 3.15 mm thick, and the race was on as In [[1964]], Büren launched an even thinner Intramatic movement, Cal. 1321, measuring 2.85 mm thick without center seconds, along with thicker central seconds and calendar options. Universal Geneve launched their 2-handed [[Universal Golden Shadow|Golden Shadow]] at the [[1966]] [[Basel Fair]] with the new [[Universal 2-66|Cal. 2-66]] which measured just 2.5 mm thick.

Another shining moment for the micro-rotor came in [[1969]] when one of three groups in the race for the world's first [[automatic chronograph]] leveraged the technology. The [[Chronomatic]] used a Büren [[Buren 1281|Cal. 1281]] ebauche to achieve a reasonable size to go to market.

[[Patek Philippe]] launched their own micro-rotor movement, [[PP 240|Cal. 240]], in [[1977]]. In the decades since, this has become their leading high-end movement and powers many of their most desirable watch models. Piaget remains committed to the design as well, using it in many of their [[ultra-thin]] movements, including their [[Piaget 12P|Cal. 12P]], the thinnest automatic movement ever at 2.3 mm, and the [[Piaget Altiplano 900P]]. [[Chopard]] is another champion, working with [[Michael Parmigiani]] and [[Philippe Dufour]] to develop a [[double barrel]] thin calibre of their own, [[L.U.C 96]].

===== See Also =====
  * {{tagpage>Micro-rotor_movements|Micro-rotor movements}}
  * [[Central rotor]]
  * [[Peripheral rotor]]


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