SRAM’s eBike Shifting Patent shows that bikes and batteries are becoming deeply intertwined. With ebikes surging in popularity both in the US and globally, manufacturers have been considering what else a large-capacity ebike battery could power in addition to propelling a bike. Headlights and taillights are obvious accessories to draw juice from an ebike battery, while SRAM has their eyes on derailleurs.
SRAM’s US patent application 2020/0283095 Electronic Cable Puller, was published on Sept 10, 2020, with Geoff Nichols as the sole inventor. It describes a wireless shifting system that’s centered around an electronic cable puller, which mounts to the frame. The cable puller is powered by an ebike’s battery.
With SRAM’s existing eTap electronic shifting system, a handlebar mounted switch communicates wirelessly with a bike’s derailleurs. An eTap derailleur has no cable, and use an internal motor to actuate shifts, powered by a small removable rechargeable battery. With all that technology bundled into a small package, an eTap rear derailleur is among the priciest rear derailleurs sold, starting at $490 MSRP for the Force model. The battery last for about 60 hours of riding between charges. Of course, SRAM has been working hard at intellectual property for bicycle gears.
This new design borrows the concept of a handlebar switch that transmits a wireless signal to initiate a shift. But instead of that signal being received by an electronic rear derailleur, it’s received by a frame-mounted box attached to the right chainstay (or another place on the frame). The box includes a wireless receiver of course, along with a motorized cable-pulling apparatus. The arrangement therefore allows use of a conventional cable-actuated rear derailleur – it’s like a robotic hand that operates a traditional derailleur.
The patent application describes an electric cable puller that “… may be powered by the centralized battery of an electric power-assist bike (“e-bike”) and may not be internally powered”. Why not include a removable battery with the cable puller? There are numerous reasons why SRM may have narrowed the patent application to exclude that arrangement, though as is common practice SRAM declined to comment on this patent application.
One reason may be that SRAM does not want to develop products that risk cannibalizing its own eTap product line – though a chainstay mounted box is far less sleek than a rear derailleur with integrated electronics. Another hurdle may be related to intellectual property, as there’s prior art around a wireless electronic cable puller: XShifter showed just such a system starting in 2016, with a Kickstarter campaign that lists over $140,000 raised. However, there very well may be patentable differences between the XShifter system and what SRAM is claiming in its patent filing.
More likely, SRAM’s focus on ebike battery power for the design speaks to the potential market. Electronic shifting is undeniably smooth, fast, user-friendly, and a very short run of cable may reduce the frequent cable tension adjustments needed by conventional derailleurs. An ebike typically has its battery charged routinely, and this new design insures there’s no concern about having to keep track of topping-up a separate derailleur-specific battery. Such an arrangement would be especially suited to fleet and rental bikes, which are often used by new or infrequent riders who find electronic shifting simple to use.
The shift buttons do require a battery to transmit their wireless signal, but the battery life is so long – about 1500 hours on SRAM’s eTap system – as to not be an issue. Rear derailleurs are also vulnerable to damage, and with this design only a conventional lower priced unit is exposed, with the costly electronics and motor separate and tucked away.
This patent application only recites a cable puller for rear derailleurs, with SRAM known for championing 1x drivetrains. But the same idea of tapping-into an ebike battery for power could be employed for other components as well. Magura has shown heated grips via ebike battery power. Expect to see more in the coming years — from alternative drivetrain technologies to dropper posts to dashboards.