Flexure is magic. Okay, that might be overselling it a bit, but the concept of a flexure is integral to dynamic mechanical engineering and might be seen by some as a bit of a black box. Flexure is the action of bending or curving, and “a flexure” is a flexible component engineered to be compliant in a specific way to achieve a desired motion or mechanical action.
That is old hat at this point: modern-day compliant mechanisms utilizing flexures are some of the most incredible creations in engineering.
This is largely due to the elimination of multiple components and integration of everything into a single part made through a variety of methods. And size is not important: compliant mechanisms exist from nano scale all the way up to human-scale gripping devices and tools.
Disney Imagineers have created complex animatronics using compliant mechanisms that mimic natural movement. But the most out-of-this-world creation comes from engineers at NASA and Brigham Young University, who designed a mechanism able to take two perpendicular rotating inputs and turn them into an omnidirectional positioning system to precisely direct thrust on satellites and probes with difficult constraints.
And while that makes me sit back in awe, the average compliant mechanism or flexure implementation is often quite simple, acting as a spring or flexible coupling to prevent damage to mechanisms under stress.
Over the last decade, compliant mechanisms and the magic of flexures have started to make their way into watches more often as brands develop components using LIGA and silicon: the Girard-Perregaux Constant Escapement and Zenith Defy Inventor’s oscillator are two great examples of what is possible.
As flashy as those pieces are, the science behind compliant mechanisms and flexures is useful in so many cases that it can pop up where you may least expect it.
Enter IWC and its new Big Pilot’s Watch Shock Absorber XPL, which is a very cool and easy-to-understand example of how flexures can both do work and prevent damage with clever design. With this release, IWC showcases exceptional durability  – and looks good while doing it.
At Watches and Wonders 2021, IWC did what it usually does and focuses on one collection for the bulk of its releases: 2021 was devoted to the Big Pilot’s Watch. Inarguably the most popular and widely known collection by IWC, the Big Pilot’s Watch is the perfect place to try out a new idea like this innovative shock absorber concept.
The main focus of the Big Pilot’s Watch Shock Absorber XPL is the technology behind the shock absorber, so the watch itself is a simple, three-hand, time-only piece with an ultra-clean dial and generally restrained aesthetic minimizing unnecessary distraction.
The dial (and therefore the movement) appears to float in the center of the case with an open portion around the edge allowing a clear view into the movement support structure that has been carefully designed to protect the watch against incredibly violent shocks.
The dial, movement ring, case, and strap are all monochrome black, inspired by stealth aircraft, with light grey printing on the dial and small hour markers at the case edge providing the only deviation from black aside from the shock absorber component.
That shock absorber is a bright gold color that almost glows from within the case as it beckons you to look inside. Interestingly, due to the specific geometric requirements of the design, the shock absorber creates an almost square profile to frame the dial as if on an old television screen. The visual is striking to say the least, but no matter how it looks the way it functions is its raison d’être.
The shock absorber, dubbed the SPRIN-g PROTECT system (I’ll return to that nomenclature), has been precisely designed to allow a very specific amount of flex under instantaneous shocks to the case. The component is basically a C-shaped ring with four pairs of leaves (eight total) that extend toward the center and help align and support the movement ring.
The leaves are connected to the ring by thin joints designed to exacting tolerances to control the amount of flex. Under a heavy shock, the entire ring and sets of leaves flex to absorb the energy imparted into the system, seeing the pairs rotate (exponentially resisting deformation) to cradle the movement as it shifts.
The shock absorber has been formed from Bulk Metallic Glass (BMG), which is a unique material with properties of both metals and amorphous solids (non-crystalline). Thanks to a technique that rapidly cools molten metals to prevent the formation of the typical crystal lattice structure, the metal can become locked in a glassy state and yet avoid the brittleness of ceramics. These special characteristics allow for some interesting properties that engineers can take advantage of.
In the case of the SPRIN-g PROTECT system it allows for very rapid flex and return to shape without bending permanently and also minimizes cracking or fatigue from repeated flexing. IWC partnered with the Cavendish Laboratory at the University of Cambridge to test the design and performance under extreme conditions. Once it was dialed in, the SPRIN-g PROTECT system was able to withstand and dissipate shocks over 30,000 Gs.
Putting that into perspective, it is the same force as a bat hitting a baseball travelling more than 600 km/h (350 mph).
Basically, you are going to lose your arm before the SPRIN-g PROTECT system maxes out its ability to absorb a shock. That is ridiculously awesome.
That feat did not come easily: it took eight years of development, research, simulation, and testing to achieve. Part of that research and development included minimizing the mass that the SPRIN-g PROTECT system had to protect. The lower the mass, the less force exerted into the ring.
The way this was accomplished was both multifaceted and yet fairly straightforward. The movement ring encompassing the mechanical heart is made from ultralight and strong titanium, reducing that component’s mass by nearly half.
Going further, the materials of some of the heavy components in the movement including the main plate and several bridges were swapped from brass to aluminum, effectively lightening the movement itself. That brought the cushioned mass down dramatically to provide a higher margin of safety for the shock absorber.
This also extends beyond the mass within the shock absorber. The case is made of Ceratanium, a proprietary titanium alloy that begins with powdered titanium and ceramic particles that is formed, machined, and sintered to create an extremely tough, light, and stable case. This light case also resists transferring force into the movement thanks to the reduction in mass. Lighter objects can always withstand higher forces because they don’t scale and are not linearly proportional.
Another consideration was the connection to the winding stem, since it couldn’t be rigidly fixed to the movement, and the screw-down crown. IWC developed a winding system allowing the stem and movement to be loosely coupled to not prohibit the shifting and displacement of the movement separately from the case.
While it may not be as mechanically flashy as a minute repeater, the combination of components in the Big Pilot’s Watch Shock Absorber XPL is truly an awesome achievement of material science and cutting-edge mechanical engineering with flexures.
I do have one gripe about the watch – and this is definitely picking nits – but it comes back to the name of that shock absorber, the SPRIN-g PROTECT system. I understand it is a play on the abbreviation for gravitational force (hence the lowercase g) but it does feel a bit uninspired. It also makes me want to pronounce it “sprin-jee” as you wouldn’t say “gaforce” but phonetically would say “jee-force.”
Just off the top of my head I can think of more interesting options such as the BMG Parachute (still within the aviation realm) or the Octo-chute (odd but fun). Or going another route, the Glass Cushion or Golden Glass to play off the Bulk Metallic Glass a bit more indirectly.
Or to make it sound like research-derived nomenclature, it could simply be called the BMG-SS (Bulk Metallic Glass Spring System).
The main reason I bring this up is that when a brand invents something it has the opportunity to have some fun and create an awesome name, but in the watch industry (and many other industries) naming almost seems like it was left until the end and those who actually had a hand in developing it played no part in naming it.
Even the Pellaton winding system found in automatic IWC watches for the last 60 years is at least named after the man who developed it, and it’s a better name. Of course, this does not really detract from the watch, but I wanted to toss it out there for IWC in case the brand isn’t too emotionally attached to the SPRIN-g PROTECT system name and it wanted to try again, perhaps adopting one of the names I suggested.
I would even let them have it, you know, maybe in exchange for one of the limited Big Pilot’s Watch Shock Absorber XPL pieces. It’s a thought.
For more information, please visit www.iwc.com/us/en/watch-collections/pilot-watches/iw357201-big-pilots-watch-shock-absorber-xpl.
Quick Facts IWC Big Pilot’s Watch Shock Absorber XPLCase: 44 x 12 mm, Ceratanium Movement: automatic Caliber 32111, 120 hours power reserve, 28,800 vph/4 Hz frequency, SPRIN-g PROTECT system Functions: hours, minutes, seconds Limitation: 30 pieces, 10 produced annually Price: CHF 80,000
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Might’ve helped to put a free-sprung balance in there if shock-proofing is what this is all about, but anyway….all this flexure science is lovely, however what really matters is does it look good? Hmm yes it does; certainly more interesting and ‘sexy’ than a lot of other models they make. Massive, though, but that’s IWC for you.
Choise of the word id.. not exactly fitting the elegance of described watch and the question is of apples and oranges. Casio is quartz mechanizm while IWC is mechanical. The fact is that in one of commercials Casio was used as a puck and it survived.
IWC is overlouding the intenion of a Shockabsorber and still fitting an Incablock for what ever reason and asking SHF 80.000 just to produce 30 pieces of watches.. In my opinion they are going crasy for what ever reasion. To many new invention are in production.many are very silly. Regards Paul Juentgen Watchmaker