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Unusual ways to change gear, Bikelopnik edition

Illustration for article titled Unusual ways to change gear, Bikelopnik edition

Because shifters are overrated.

So, this is the Fichtel & Sachs Torpedo Duomatic 102 hub, a kickback-shifting 2-speed internally geared hub with coaster brake, intended primarily for folding bicycles, from 1964.


Similar hubs are the Duomatic 101 (the same thing without the coaster brake), earlier Bendix 2-speed Automatic hubs from the 1960s, the later Torpedo Duomatic R 2110 from circa 1970, and the modern Sturmey-Archer S2C and S2K hubs. (There was also a fully automatic variant of the R 2110, known as the A 2110, which SRAM has reintroduced as the Automatix. Shimano had their own 2-speed automatic hub, the AB-100, in the 1970s as well. These, however, don’t have the kickback shift functionality, instead using flyweights to manipulate their ring gear pawls.)

The Torpedo Duomatics share a lot with the 3-speed Torpedos of the era, but have an entirely different shifting mechanism. So, in a normal 3-speed hub, like those made by Sturmey-Archer, the sun gear is fixed on the axle (which is bolted firmly to the frame, it’s not turning), and the planet carrier and ring gear can be connected alternately to the hub shell and the input driver. Low gear is formed by connecting the input driver to the ring gear, and the hub shell to the planet carrier, middle gear is formed by connecting both to the ring gear (bypassing the gearing entirely), and high gear is formed by connecting the input driver to the planet carrier, and the hub shell to the ring gear. A shift cable moves a clutch in and out to select the configuration.


In the Duomatics, low gear is unavailable - first gear is a direct drive, and second gear is the high gear. The planet gear is always connected to the hub shell through a set of pawls (I believe at the brake assembly), and the ring gear has pawls can be engaged to the hub shell through a driver ring as well. When this happens, the hub shell will overrun the planet gear and its pawls, causing the hub to click in high gear.

Engaging those ring gear pawls is where it gets a bit interesting, though. When you backpedal, a control ring is allowed to rotate, that control ring affecting whether the ring gear pawls are retracted or extended, either disconnecting it from, or connecting it to the hub shell. This means that no shifter is required, you simply backpedal and get the other gear. And, backpedal hard, and you get both a shift and braking, on models with a coaster brake.

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