Lightning In A Bottle: An Electrostatic Accutron Spaceview 2020

To most of the folks who’ve heard the name “Accutron,” it means a range of watches made with electronic movements in which the balance wheel of a conventional watch is replaced with a vibrating tuning fork, controlled by a transistorized circuit and driven by a battery. The original Accutron watches were first introduced in 1960 and production ceased by the mid-1970s as quartz watches (which, incidentally, are also tuning fork watches except that the tuning fork is much tinier and made of quartz) became increasingly affordable and eventually ubiquitous, as well as inherently more accurate than tuning fork watches.

In 2008, Citizen acquired Bulova and along with it, the Accutron brand and in 2020, relaunched the first new Accutrons in decades – the Spaceview 2020 models. Rather than reproduce the tuning fork technology of 1960, however, the new Accutrons debuted a new-to-watchmaking system for charging and driving a quartz watch: the electrostatic drive system. Along with the new charging and driving system, the new Accutrons also have a movement architecture and overall design that’s a shout-out to the most popular of all vintage Accutron models – the open dial Spaceview Accutrons.

The Accutron Spaceview 2020 has three apertures on the dial; the single large opening at 10:00 shows the driving electrostatic rotor for the seconds hand, while the two lower openings show the charging rotors. The green color of the movement bridge is a reminder of the green circuit board of the tuning fork Spaceview. In the original tuning fork watch, the tuning fork had copper-wound coils allowing it to be driven at a specific frequency by the timing circuit; in the Spaceview 2020, the copper coil shown is for the stepper motor that drives the hour and minute hands.

Electrostatic motors have been around for several centuries, surprisingly enough – some of the first were developed by none other than Ben Franklin, in the 1750s, although they were relatively low torque and today, electric motors mostly run on the principles of electromagnetic induction. A conventional electric motor has two basic parts: a rotor and a stator, and when an alternating electric current runs through their respective coils, a magnetic field is induced, which  causes the rotor to turn, thanks to the attraction and repulsion of positive and negative magnetic fields. If you’ve ever played with permanent magnets and felt the force pushing the poles together or pushing them apart, you’ve experienced the forces inside a conventional electric motor directly.

An electrostatic motor doesn’t use the attraction and repulsion between induced magnetic fields – instead, it uses the attraction and repulsion between areas with opposite electrical charges. These areas are caused by an excess of electrons in one area relative to another, and just as with magnets, you’ve probably directly experienced static charges. If you’ve ever rubbed your feet across a wool carpet and then touched a doorknob (or, more enjoyably, some hapless friend’s nose) and seen a spark jump, you’ve seen static electricity – more specifically, you’ve seen a static electric discharge.

Likewise, if you’ve ever done the little experiment of rubbing a balloon on a wool sweater, and watching it attract someone’s hair (or pieces of torn paper, in another version of the experiment) then you’ve seen the attraction of regions of differing electrical charge.

The two electrostatic rotors carry a negative electrical charge and are sandwiched between two upper and lower electrodes. They’re geared to a mechanical rotor, which causes them to turn in the same way that an automatic winding rotor in a conventional mechanical watch winds a mainspring. The resulting electrical current charges a capacitor which in turn, drives the quartz timing package, the stepper motor for the hour and minute hands, and, most noticeably, the electrostatic motor that drives the seconds hand. This is the same principle seen in so-called Wimshurst electrostatic generators, whose spinning rotors and electrical arcs are associated with the tale of Frankenstein.

The electrostatic drive rotor works the same way the charging rotors work, but in reverse. Electrical current from the capacitor causes an electrostatic charge to accumulate on fixed electrodes, which attract and repel charged areas on the rotor, causing it to turn. This in turn drives the seconds hand, in a smoothly flowing motion.

Normally the seconds hand of a watch – any watch – moves in increments; in mechanical watches those increments correspond to the frequency of the balance. Each time the balance swings, it unlocks the escape wheel, which advances one tooth and this in turn advances the seconds hand. A balance with a frequency of 2.5Hz has a balance that beats five times per second, so the seconds hand advances five times per second in discrete jumps. With a quartz watch it’s a little more complicated – a typical quartz oscillator has a frequency of 32,768Hz, and so the quartz timing package counts the oscillations until 32,768 oscillations have passed, and then advances the seconds hand one second, with the stepper motor. The tuning fork Accutron watches had seconds hands that looked as if they were advancing smoothly to the human eye, but they were in fact advancing 360 times per second – once for every oscillation of the tuning fork (although the distinction’s a little academic – the human nervous system perceives any motion of 24 increments per second or faster as a continuous motion, which is why the frame rate for movies historically was 24 frames per second.

Actual continuous motion in a seconds hand is extremely rare in watchmaking; I think the only other example in current production is Grand Seiko’s Spring Drive. These use a different technology than the electrostatic charging and driving system – the smooth motion in Spring Drive is thanks to a magnetically braked glide wheel;  both Spring Drive and Accutron electrostatic watches are ultimately regulated by quartz oscillators. What the the Accutron Electrostatic watches offer is not only a smoothly gliding seconds hand, but also a unique visual and technical experience.

I sometimes wonder what Ben Franklin would have made of the electrostatic Accutrons – he was unable, as far as I know, to come up with any practical application for them, although he did suggest that you could use one to, of all things, power a rotisserie. Today, they’re mostly used in much smaller applications; typically they can be found as actuators in MEMS (Micro Electro Mechanical Systems) where their relatively low torque in comparison to the electromagnetic motors in, for instance, power tools and electric cars, is more than compensated for by their miniaturization.

In watchmaking there’s in a very literal sense nothing else like it – a watch with direct connections to everything from the earliest days of modern scientific research into electromagnetism, to the tuning fork-controlled wristwatch (the single biggest advance in precision timekeeping since the invention of the balance spring) to the 20th century revolution in art and design that made using the functional components of a building or a machine as an intrinsic part of its aesthetics, as seen in the original Spaceview. And, of course, there’s the electrostatic drive system – which works on the same principle of static electric accumulation and discharge that produces lightning.

Contact Us For Pricing And Availability