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HomeCyclingPatent Patrol: SRAM's Self-Charging Auto-Shifting Rear Derailleur

Patent Patrol: SRAM’s Self-Charging Auto-Shifting Rear Derailleur


Will SRAM quickly debut a self-charging wi-fi mountain bike derailleur with a dynamo generator inside? SRAM filed a patent on November tenth, 2022, detailing an digital rear derailleur with the means to re-charge itself while in use, negating the necessity for even a medium-sized detachable battery that requires charging off-the-bike. The 28-page doc describes using a generator coupled to the derailleur cage that may be activated to repeatedly cost the batteries by advantage of the rotation of the higher pulley wheel whereas pedaling.

An on-board energy-harvesting system will surely cut back pre-ride faff related to charging detachable batteries. It will additionally make any future SRAM AXS drivetrain carrying the know-how a viable choice for extremely long-distance endurance racers who now in any other case have to hold spare batteries. Nonetheless, one can think about that the mechanism described would end in some lack of watts from further drag inside the drivetrain, provided that it’s taking its vitality from rotation of the higher pulley wheel throughout pedaling.

We definitely shan’t be estimating what number of watts, however we will provide you with an outline of among the novelties described on this fairly unusual-looking derailleur which will or could not make it to manufacturing. Right here’s a more in-depth take a look at SRAM’s Self-Charging Auto-Shifting Rear Derailleur.

Characteristic photos annotated by Cory Benson

SRAM’s Self-Charging Rear Derailleur Idea

sram self-charging auto-shifting rear derailleur generator new shifting mechanics
SRAM Digital Self-Charging Rear Derailleur idea; Mounting Portion and Parallelogram (mild gray), Clutch and Shift Motor (yellow and inexperienced), Generator (darkish blue), Generator Gearbox (mild blue), AXS Pairing Button (crimson) and an LED indicator (small inexperienced dot)

The patent in query (US 20220355900 A1) particulars a bicycle derailleur that includes an energy-harvesting system. The primary few paragraphs point out one of many drawbacks of present digital derailleurs; the inconvenience of getting to recharge the battery, with the inherent threat of it operating out of juice while out on an extended bike experience. These fortunate sufficient to personal an digital shifting drivetrain will know this all too nicely; maybe not a lot as a result of they’ve run out of cost mid-ride, however extra probably as a result of they’ve forgotten to re-charge the battery earlier than heading out for his or her subsequent experience. One can think about the frustration.

SRAM’s patent revealed final November describes a self-charging derailleur that will eradicate this problem, which means its proprietor would not have to worry over the cost state of the battery. They may use that psychological bandwidth to worry over extra essential issues, like hydration, fueling, and remembering their family members’ birthdays, for instance. (Ed’s observe: We really feel like J-M could have lately missed an essential birthday!)

The derailleur depicted all through the doc appears to be like to be extraordinarily compact. {The electrical} generator system, clutch, motor, shifting electronics and batteries are all housed on the derailleur cage meeting (as a substitute of their present location, additional aft on the b-knuckle), coupled to the rotation of the higher information pulley. That makes for a really peculiar-looking derailleur cage certainly, but additionally (I think about) a fairly costly one, too, ought to it ever should be changed.

sram self-charging rear derailleur extended larger cogs
SRAM Self-Charging Digital Derailleur in an prolonged place; the higher information pulley (21), pushed by the chain, drives an inner pinion gear to activate a generator to recharge a battery or batteries on-the-go, even at gradual pedaling speeds

So, how does it work?

Like most patents, this one particulars a lot of other ways through which it’d obtain its main aim, taking care to guarantee the reader that the mechanisms described inside “aren’t supposed to restrict the scope” of the invention. The primary embodiment describes using a generator that’s housed on the derailleur’s cage meeting, which will be activated by way of a lot of completely different mechanisms so as to re-charge a battery or batteries.

The gearing contained in the generator of the SRAM Digital Self-Charging Rear Derailleur

The primary mechanism described entails coupling rotation of the cage’s higher pulley wheel (by way of 35 in Fig. 30), to drive a pinion gear to activate a generator. Inside that mechanism, the patent describes use of a spur gear (339), pinion gear (338), belt, and an inner pulley wheel (41) to activate the generator base (46), stating a most well-liked gear ratio of 33.75:1. So, for each single rotation of the cage’s higher pulley wheel, the pinion gear inside {the electrical} generator system rotates 33.75 occasions. That will counsel that the generator is most effective at very excessive speeds.

On this state of affairs an, albeit very small, portion of the rider’s enter on the cranks is getting used to show the generator. So, it’s cheap to imagine that a few of your treasured watts can be misplaced to {the electrical} generator system so as to cost the derailleur’s battery whereas pedaling. That stated, we think about that loss to be a lot lower than the losses related to a bigger hub dynamo.

The patent additionally describes use of a clutch (290) inside the electrical generator system that forestalls rotation of the gears when the rider back-pedals. Clearly, such a state of affairs will not be so frequent, however it does sometimes occur to various levels on some full suspension mountain bikes throughout pedal kickback occasions that consequence from chain development.

The patent’s 22 pages element use of transistors, resistors, and capacitors, the features of which I shan’t faux to grasp past offering a clear stream of electrons to make the battery blissful. However, the lengthy and the wanting it’s this: the on-board generator is, ultimately, recharging the derailleur’s batteries in order that it, theoretically, ought to by no means run out of cost while on a experience. This might be a game-changer for the ultra-distance contingent who can’t run the chance of a battery shedding cost mid-adventure or endurance race, for concern of getting to single-speed it till they arrive at their subsequent refueling spot.

New Shifting Mechanics

sram gx eagle axs wireless rear derailleur shown on a mountain bike while riding
A present SRAM AXS GX Rear Derailleur with a big detachable battery housed off the again of the B-Knuckle

Fig. 28 of the SRAM Patent Utility reveals utterly new shifting mechanics, too. On the present SRAM AXS rear derailleurs, the shifter motor and battery are housed on the aft b-knuckle of the derailleur, in between the rear pivots of the parallelogram linkage that mediate shifts. Right here, on the brand new self-charging digital derailleur idea, the shifter motor is housed on the cage meeting, sequentially driving pinion gears, spur gears, a screw (81), a nut (91), and finally a drive pin (97), to rotate the outboard hyperlink (6) of the parallelogram so as to execute a shift.

sram self-charging auto-shifting rear derailleur patent energy-harvesting system cage-housed motor shifter mechanism

Sorry, you shan’t be getting any extra element out of me than that. Nonetheless, must you want to immerse your self within the mechanics of all of it, I can verify it’s all painstakingly spelled out on pages 8 and 9.

It strikes us that a variety of essential (and certain costly) componentry is positioned on the, arguably, extra weak a part of the derailleur – the cage. Regardless of this, the patent doc reads, “the motor and/or {the electrical} generator system could also be mounted on and moveable [sic] with the cage. If broken, the cage, together with the motor and electrical generator system, could also be shortly and simply changed with out having to switch the opposite parts of the derailleur”.

We’ll name the modular alternative idea a comfort prize.

When within the small cog/huge gear, that greater mechanism on the cage does stick out fairly removed from the airplane the place the derailleur hanger bolt contacts your body (15 beneath). However as you shift into a neater gear/greater cog, the majority of the derailleur does seem to tuck up below the chainstay, staying near the cassette.

A top-view of the SRAM Self-Charging Rear Derailleur; Fig.3 reveals the derailleur positioned to service the smaller cogs of the cassette, whereas Fig. 5 reveals it positioned for the bigger cogs, a decidedly NOT parallel motion that higher aligns with the angle of the bike’s chain

Lastly, an auto-shift operate can be described. Diodes and resistors inside the electrical generator system are used to sense the velocity of the generator, which might then be used to find out the velocity of the chain pulley, and subsequently the velocity of the chain. That data, taken along with data delivered by different sensors on the bike (on the cranks and rear wheel, for instance) might be “used to carry out an computerized shifting algorithm which retains the gear ratio at a preferable ratio for the rider”.

Will the SRAM Self-Charging Derailleur Make it to Manufacturing?

Who is aware of. We now have approached SRAM for touch upon the proposed know-how, however are but to listen to again. We’ll maintain you up to date ought to we be taught extra in the end.

SRAM XX1 Eagle AXS BlackBox prototype, photo by Michal Červený, detail

The worst-kept secret within the bike business proper now must be the approaching arrival of a new SRAM AXS XX drivetrain. We now have coated this extensively as varied Black Field Prototypes have cropped up on Execs’ Cross-Nation Race Bikes. Evaluating these pictures with the diagrams seen right here, it is vitally unlikely any of the self-charging know-how described herein can be a characteristic of that drivetrain. We reckon it is going to be a number of years earlier than we see something like this rolled out to manufacturing, if in any respect.




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