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I am a long-time watch nut, and I loved this write-up - it concisely explained what makes this mechanism unique and was most educational.

Fun to see a departure from the norm - until this, the probably largest innovation horology over the past couple of hundred years was George Daniels' coaxial escapement (which basically eliminated friction from the equation, ensuring all transfer of energy in the escapement took place between components tangential to each other, allowing for excellent long-term precision)

The plural of anecdote is not data, but my ten year old Omega with coaxial escapement (in a c.2500C) is still accurate to within a second a day without ever having been serviced. That,in my book, is remarkable.

(It is due for a service soon; I do not intend to run it into the ground...)

> the probably largest innovation horology over the past couple of hundred years

There was this little thing called the quartz revolution though :) Just because it turned out you can make really cheap watches with it doesn't make it less of an innovation.

But limiting the field down to mechanical watches, there is also Seiko's springdrive which manages to combine the durability of mechanical watches whilst approaching the accuracy of quartz watches by using a complete new method of escapement.

Co-ax movements are surely a worthy innovation, but I wouldn't want to claim it was the most significant horological innovation of the last few centuries.

Fair point. Spring drive is a very fascinating concept and one could debate for weeks on end in the right (or, rather, wrong) circles whether it or co-ax holds the top spot. (Or whether the spring drive is even a fully mechanical movement or a hybrid!)

(And I should have been more precise - I meant in mechanical horology; my apologies)

Not that there's anything wrong with quartz (except its inherent inaccuracies; I say this tongue-in-cheek as my interest in all things horological extends to my having a rubidium standard in the man cave - a hand-me-down HP 5065A. Sadly, my wife does not appreciate the beautiful engineering, and suggested a Seiko wall clock would have to do for our everyday time-keeping needs...)

> one could debate for weeks on end

That is certainly and certifiably true :)

Although I'm very fond of Springdrive (and Seiko in general), it's just an example that I thought would be more recognisable than, say PP's use of ceramic components. I wouldn't want to claim any of these advancements as more significant innovations than Co-Ax escapements in what is increasingly an art-for-the-sake-of-art (or tech-because-we-can) endeavour anyway.

It's best just to marvel and to start thinking of how to explain the expense to the significant other.

How can we debate whether the spring drive's fully mechanical or not? It's got a quartz oscillator and an integrated circuit.

Well, for one, the escapement doesn't depend on the quartz crystal for timekeeping, but on magnetic induction.

Spring drive would theoretically work without the quartz components. Seeing how they would generate an electrical current because of the principle, they build a tiny generator to drive a circuit that adjusts the escapement, but doesn't run it.

Also, Spring Drive depends on a fully mechanical wheel train and barrel spring to function; it could not be made to work with a battery.

So what exactly constitutes mechanical and what does quartz here? Is it the wheel train? Does electro-mechanical count as mechanical? Is the mere presence of a quartz crystal in a secondary circuit enough to call it a quartz?

I found it easier to see it a as a new different system for timekeeping instead of trying to place it on an arbitrary scale between "fully mechanical" and "quartz."

> Well, for one, the escapement doesn't depend on the quartz crystal for timekeeping

No, it uses the quartz crystal for timekeeping. It keeps time like any other digital watch, only it outputs that time by controlling the rotor's speed, and gets its power from the rotor.

It could keep time mechanically instead and still use electronics to maintain the rotor's speed. But in fact it uses a quartz crystal.

How does the spring drive actually work? What is the mechanism which keeps it moving at a consistent speed? A quick google only turned up rather vague descriptions.

At the heart of every mechanical watch lies a coiled spring. Within that spring energy is stored that wants to be released.

This energy is released through the wheel train, which is a set of cogs with reductions (some of them attached to the hands).

Left to its own device this system would just spin as quickly as possible until the spring is unwound.

To prevent this, somewhere in the train there is something called a lever escapement. Simple put, this puts a stick in a cog at regular intervals to prevent it from spinning and unwinding freely. This stick is timed by a weight that spins from left to right. This stick literally is what makes watches tick, since that's where the ticking sound comes from.

Spring Drive doesn't poke a stick into a wheel to prevent the system from freely unwinding. What it does do is add magnets to the wheel and stationary coils around it. The wheel can't spin freely since it has to overcome the magnetic induction as the magnets pass the coils. That's the reason SpringDrive doesn't tick and the hands glide instead of stopping and starting.

If it's still unclear, try looking up escapement levers first. There should be a lot of clear animated explanations online.

I understand (roughly!) the basic idea of a watch mechanism, and how mechanical escapements work.

What i don't understand is exactly how the spring drive keeps the wheel moving at a constant speed.

I appreciate that this involves magnets, and eddy currents induced by those magnets, but that's a description, not an explanation. What is the mechanism, physically and mathemetically, that keeps the speed constant?

From a physics angle we're mostly dealing with electromagnetic induction. Faraday's law of electromagnetic induction states:

"that a voltage is induced in a circuit whenever relative motion exists between a conductor and a magnetic field and that the magnitude of this voltage is proportional to the rate of change of the flux".

The magnetic field here is attached to the glide wheel (rotor). The conductor is some stationary spools placed near the glide wheel. This means the voltage output depends on how fast the glide wheel spins (rate of change of the flux).

The other part of Springdrive comes from Lenz’s Law of Electromagnetic Induction:

"the direction of an induced electro magnetic field is such that it will always opposes the change that is causing it"

That means that the current creates a electromagnetic field of its own that opposes the changes in the magnetic field that caused it.

So that opposing field depends on the rate of flux according to Faraday. That rate of flux directly correlates to the passage of time (the spinning of the glide wheel).

By adjusting the placement and configuration of the circuit (the spools) we can influence the flux, thereby influence the induced voltage, thereby influence the induced magnetic field that opposes the change that is causing it, which is the spinning of the rotor that correlates to the passage of time, to a degree that hopefully is around 1 second per second (or 1 rotation of the glidewheel per 1/8 second).

Note that if the glide wheel accelerates for some reason, the change of flux changes, the voltage changes, and the opposing magnetic field increases, forcing the speed of the glide wheel down. On the other hand, if the glide wheel slows down, the opposing magnetic field decreases and allows the glide wheel to spin faster.

So technically the "smooth" second hand isn't smooth at all, but slows down or speeds up about 8 times a second, so it's not exactly "at a constant speed," but since it's not a start-stop motion, it sure looks smooth to an observer.

Inertia. The torque applied by electromagnetic force on the rotor plus that of friction and air resistance equals the torque applied (indirectly through a gear train) by the mainspring. The net torque is zero and the rotor keeps going at the same rate of rotation.

The integrated circuit counts how many times the rotor has spun compared to how many quartz crystal oscillations have happened and adjusts the electromagnetic force somehow. My guess is by increasing/decreasing the power passing through some resistor (creating heat).

There's one basic question I couldn't figure out from the article. Where is the spring that you wind up and that stores the "power reserve of about 60 hours"? Is it part of the silicon? Or is it external? I figured out that the three crescent-shaped parts are springy ("flex laterally to provide a restoring force as the oscillator vibrates through six degrees of amplitude"), but it doesn't look like there's anything else that could stretch/relax over 60 hours. My sense of intuition is useless, of course, at this scale and with these materials.

This video may help, as you get to see the movement in action: https://youtu.be/xWh0p9Irznw

It doesn’t clearly show the mainspring, however at around 10:45 you can see the small gear spinning. That is being driven by the mainspring, and if you removed the escapement it would spin super quick until the mainspring was unwound.

It’s the constant rocking back and forth of the regulator that limits the speed that small gear (called the escape wheel) can rotate, therefore limiting how quickly the mainspring releases it’s energy.

Indeed it helped. Thanks.

That spring will be connected to drive the escapement. The resonator is the equivalent of a pendulum, even though it contains a spring. The escapement wheel is driven by a non-constant force from the drive spring. The resonator regulates its motion to tick at a regular rate, and in so doing draws power to keep resonating. The rest of the watch is driven from the same source.

The energy is stored in a big spiral spring, the mainspring, as in a conventional mechanical watch. The oscillator does away with another spring, the balance spring.

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