CeramicSpeed Driven shaft drive steps closer to reality: Now it shifts!
CeramicSpeed made a huge splash at last year’s Eurobike show with the debut of its truly radical Driven ultra-low-friction shaft drive concept. It really was little more than a concept back then, too, and more than a few critics dismissed it as a flash in the pan that would never see the light of day.
CeramicSpeed has been hard at work over the last year, though, and not only does Driven look a lot more refined than before, there’s also a new variant for full-suspension mountain bikes, and the system now even shifts gears thanks to a novel wireless electronic actuator hidden away inside the driveshaft.
Still think it’s a pipe dream? Maybe it is. But then again, maybe it isn’t.
A dual-clutch transmission for bikes
“After the buzz from Eurobike, we decided that we needed to take this further,” said CeramicSpeed’s chief technology officer, Jason Smith. “That was a concept; it wasn’t rideable, it wasn’t shiftable, there was still a lot left to do to get it to reality. So what we’ve been doing the last year is getting it closer to that.”
It still isn’t in production. But it’s getting closer.
The biggest advancement by far is that Driven — once just a singlespeed proof-of-concept — can now shift gears.
Together with a student engineering team from the University of Colorado in Boulder, CeramicSpeed’s first stab at a shiftable Driven drivetrain used a rear pinion cluster that moved axially along the drive shaft. This could certainly work in theory, but shifts were only possible at areas of the cassette where the teeth on adjacent cogs lined up perfectly. There was also the issue of timing and load. The timing had to be absolutely perfect, and shifts under load were basically impossible.
The colored sections of this early prototype show where a solid drive pinion cluster could easily move back and forth between adjacent cogs.
The next iteration used a split pinion cluster that essentially allowed for two cogs to be engaged simultaneously, similar in theory to how the dual-clutch transmission works in many modern cars. During a shift, one half of the pinion cluster would continue to transmit torque to the current cog, while the other half would advance to the next easiest (or hardest) gear, all without skipping a beat.
However, even this system still had to wait until the teeth on adjacent cogs lined up perfectly for a smooth, jam-free shift, which also meant that shift speed was highly variable. But then CeramicSpeed came up with the idea for the “torque decoupler”.
This latest iteration of the shiftable prototype still uses a split pinion cluster at the rearmost end of the driveshaft, but one of the cartridge bearings rides on a spring-loaded carrier. During a shift, that single cartridge essentially acts as a timing bridge between two adjacent cogs so that it no longer matters where the teeth sit relative to each other; even if the teeth don’t line up, the torque decoupler allows for enough independent movement between the pinion cluster and cassette that the system can still effectively engage two gears at once.
A small spring-loaded “torque decoupler” makes up for any differences in timing between the cassette teeth and drive pinion halves to prevent jamming. During a shift, that spring-loaded bearing momentarily disengages drive torque so that the incoming drive pinion half can line up with the cassette teeth.
But how exactly do those two halves of the pinion cluster move, anyway? That’s another brilliant little feature of the design.
Since each half of the pinion cluster not only has to move in a specific order — one half is always the “leader” and the other is always the “follower” — but also has to be able to move in two directions, one might assume that there are two separate electric motors and two separate actuators inside the oversized carbon drive shaft. But CeramicSpeed knew that such a design would be too heavy, too big, and too power-intensive to fit in the space allotted, so Smith and his team came up with something they’ve dubbed a “hysteresis drum”.
The “hysteresis drum” sits inside the oversized carbon fiber drive shaft, and mechanically guides each half of the split pinion cluster. Photo: CeramicSpeed.
That hysteresis drum is basically a small cylinder with a complex pattern of ramps, channels, and gates machined into its surface. On the inside of each pinion cluster half is a trio of spring-loaded pins. During a shift, those pins ride inside the channels on the drum, which is rotated with the single electric motor. The direction of rotation dictates which way the pinion cluster “leader” moves, while that system of ramps and gates always ensures that the “follower” never moves first.
Confused? Don’t feel bad; just watch the video above and be mesmerized.
Either way, CeramicSpeed is claiming some incredibly quick theoretical shift speeds. According to the company’s calculations, Driven should be able to change gears in as little as 20ms. Current actual speeds are quite a fair bit slower than that, but still admirably quick.
The secret to better aerodynamics
CeramicSpeed revealed last week that it had conducted some wind tunnel testing at Specialized’s facility in Morgan Hill, California, saying that the specially modified Driven-equipped Specialized S-Works Venge was “3% more aerodynamic” than the same bike with a standard drivetrain. Put another way, that improvement translates to about eight seconds of time savings over 40km at race speeds.
But why is that exactly?
According to Smith, the secret lies not so much in what Driven adds, but rather what it takes away. Derailleurs aren’t exactly known to be particularly aerodynamic, and getting rid of them helps smooth out the airflow in that area significantly. CeramicSpeed also reshaped the rear cassette, making it more of a cone than a flat plate, which allowed the driveshaft to more closely follow the chainstay and the crankarms to sit at a more conventional Q-factor.
CeramicSpeed has developed a neat two-piece cover that secures with magnets.
Interestingly enough, that sleek-looking 3D-printed cover that shields the rear pinion cluster and cassette looks like it’d contribute a lot to the system’s aerodynamic efficiency as well. But in reality, Specialized’s test engineers couldn’t detect any real differences either way, which suggests most of the improvements are happening further upstream.
Mountain bike-ready — sort of
Up until now, Driven has mostly been viewed as a road-only thing, but CeramicSpeed clearly sees things differently, based on the specially modified Canyon Lux full-suspension mountain bike prototype the two companies also worked together to produce.
Far from abandoning Driven as just a one-off design concept, CeramicSpeed has continued to expand its development since it broke ground last year. New this time around is a mountain bike application that CeramicSpeed not only claims to run more efficiently, but could save as much as 500g or so if fully brought to production.
The major challenge here was how to handle the change in effective chainstay length as the rear suspension moves through its travel. The solution that CeramicSpeed developed is a telescoping carbon fiber driveshaft that maintains the relation between each pinion cluster, the cassette, and the chainring, but automatically adjusts its length in between.
CeramicSpeed makes the same efficiency claims here as it does with the road version, but in this case, the bigger benefit may be weight, not friction. Modern 1×12 mountain bike drivetrains offer tremendous gearing range and remarkable chain security, but those monstrous cassettes, super long rear derailleur pulley cages, and powerful clutches also add up to a fair bit of weight, with nearly all of it situated right around the rear axle.
The drive shaft telescopes as the suspension moves through its travel so as to maintain contact between the front and rear pinion elements.
Although a production version of Driven is clearly still a ways off, Smith’s team of engineers estimates that a complete setup could potentially shave as much as half a kilogram from a bike that currently runs a top-end setup from Shimano or SRAM, which, together with the improved efficiency, would make for quite the enticing proposition for cross-country racers looking to gain every possible advantage.
Still a lot of questions
Needless to say, Driven is still far from being available on store shelves, and there remains an awful lot of work to be done — not to mention plenty of questions left to answer.
For one, it remains unclear just how much load the shiftable version could even handle. Currently, CeramicSpeed’s newly rideable prototype is only meant to withstand about 200W, which is barely the threshold value for many average cyclists, and roughly a tenth of what a top-level pro sprinter can produce.
Even if this prototype were fitted with the new shifting mechanism, it’s clear that there isn’t enough room for the drive pinion to access the full cassette. CeramicSpeed insists, however, that this is one of the issues that would be solved if a dedicated frame were used instead of one that was modified for the purpose.
CeramicSpeed also doesn’t have a shifter designed yet. Although the shiftable prototype operates wirelessly, it’s triggered by a rather big and bulky box that clearly isn’t anywhere near as small, light, or ergonomically designed as it would need to be.
On the mountain bike front, the theoretical performance improvements sound nice, but what about durability? CeramicSpeed envisions that the rear end of the drivetrain would likely be enclosed to keep rocks and sticks from getting jammed back there, but that cover would only protect against bigger stuff; one can only wonder what would happen during an especially muddy ride. And would the front area be covered as well?
All of this fits inside the carbon fiber driveshaft. And keep in mind that this is very much a prototype, meaning a production version would most likely be much smaller.
CeramicSpeed’s new partnerships with Specialized and Canyon clearly paid dividends in terms of how finished the latest prototypes look, and both companies have apparently expressed some interest in using Driven if it gets closer to being a viable transmission option. But even if CeramicSpeed is able to do that — and that’s a big “if” — how much will those companies be willing to invest in dedicated frames that will have to be designed from the ground up to work with Driven? And who else might be interested?
Questions aside, Driven clearly has the potential to be the first major development in bicycle drivetrains in decades. It’s far from a guarantee that it’ll see the light of day as an actual production item — or live up to its heady performance claims — but what a day it’d be if it really does.
Here’s to hoping.
CeramicSpeed’s latest Driven prototype test mules certainly look a lot more finished this time around. As a sign that the industry is taking this work seriously, Specialized and Canyon have apparently both expressed interest in working more closely with CeramicSpeed to bring Driven to market once the development moves further along.
The current prototype looks a lot better than the one CeramicSpeed showed off last year, but it still has a ways to go. It’s not hard to imagine how this could be properly integrated into a frame with a more concerted ground-up effort with a manufacturing partner, though.
The newly tucked-in driveshaft helps with both aerodynamics and Q-factor.
This definitely looks a lot better than it once did.
Currently, the hybrid ceramic bearings used in the prototypes aren’t equipped with any shields or seals. That would obviously change if/when the system went to production.
There are still so many questions left to be answered, but it’s encouraging to see that CeramicSpeed is continuing to develop the Driven concept.
Critics were quick to write off CeramicSpeed’s radical Driven shaft-drive drivetrain when it was first shown last year, saying that it clearly was nothing more than a one-off showpiece since it couldn’t shift gears. Well, now it can.
Inside this newly oversized carbon fiber driveshaft is a motor, wireless control unit, and innovative ramped guide system that moves the drive pinion axially along the shaft. Well, that’s in theory, at least. The prototype fried a circuit board hours before I visited the office in Boulder, Colorado, so this shaft is actually empty.
CeramicSpeed’s now-shiftable Driven drivetrain is analogous to a dual-clutch transmission in a car. The drive pinion is split in half, and each half can move independently. During a shift, the leading half advances to the next gear, and both halves are momentarily engaged. In this image, the system is shifting to a harder gear.
Here, the Driven system is shown shifting to an easier gear. As the pinion half on the left disengages from the cassette, the other half simultaneously engages the next cog.
The mechanism CeramicSpeed has developed for the Driven shifting mechanism is quite ingenious, comprising a series of carefully machined ramps and gates that move the drive pinion halves back and forth. Just moving the halves around isn’t hard, though; what’s tricky is making sure that it’s always the same half that’s moving first in either direction without having to resort to two separate motors and drive systems.
Shown in this proof-of-concept printed prototype is the trio of pins that run along the tracks in the guide cylinder.
The original Driven cassette was pan-flat. The new one is dished to more closely follow the profile of the wheel’s spokes, which also helped CeramicSpeed tuck the system in closer to the centerline of the bike for better aerodynamics.
Since the drive shaft has to move with the suspension, spherical bearings are used at either end.
The Driven chainring – at least in this form – isn’t much bigger than a standard chainring, so ground clearance shouldn’t be an issue.
Aside from the safety concerns suggested by the rear cluster’s meat grinder-like appearance, there’s also the concern that trail debris could get jammed in the mechanism. Ultimately, CeramicSpeed envisions that the drivetrain will be at least partially enclosed.
The black anodized finish lends this prototype cassette a more refined appearance.
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