New E-Bike Crankset Is A Chainless Pedal-By-Wire System That Incorporates Regenerative Braking - CleanTechnica

cleantechnica.com New E-Bike Crankset Is A Chainless Pedal-By-Wire System That Incorporates Regenerative Braking - CleanTechnica

Cixi, a French company which specializes in "green active mobility solutions," has developed its own version of a chainless drivetrain, which it calls a Pedaling Energy Recovery System (PERS)

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I personally can't see this being the future, but perhaps I'm not visionary enough. But I want to focus on the efficiency argument, since this might be a supposed benefit we can quickly dispense.
A cursory search for "bicycle chain efficiency" reveals the Wikipedia article on bicycle chains stating an "up to 98%" figure, as well as an article with experiments assessing front derailleur sprocket counts , and then a thesis PDF from the year 2000. I won't bore you by summarizing the details, but all the graphs in Chapter 7 (Chain Efficiency) of the thesis PDF show that for input power above 100 W, the lowest efficiency was still 92%. And importantly, increases with more power applied, measuring a peak of 97% at 205W (PDF page 179).
This range of 92-97% from the PDF agrees with the other article, and the Wikipedia page's headline figure as well. Since this chainless bike would necessarily be electric, we can assume an equivalent chained, mid-drive ebike would have more than 100 or 200 W of input power, which means the chainless bike should be compared against the higher efficiency range of a chained ebike. For reference, today's mid-drive ebikes have motor outputs of 250 W and up, plus whatever the rider delivers.
For any discipline of engineering, it's really hard to make gains when your competition leaves you only 3% to vie for. This is the space that F1 and spacecraft have to deal in, whereas consumer goods like everyday bicycles cannot hope to engineer their way beyond the phenomenal efficiency that is 92-97%. We can fairly confidently rule out mass-market adoption of this chain less technology.
But what these references do not test is the impact of chain length, when elongated by several meters. A prior holder of The World Record For Longest Bicycle built it as a tandem bike, probably because a chain spanning the 35 meter behemoth would be untenable. That bike could potentially be reduced to a single rider by using this chainless technology.
So if you're building a bicycle where the driven wheel is far enough away -- like the length of the first powered, heavier-than-air flight in 1903 at Kitty Hawk, NC, USA -- then maybe this could indeed be the technology for you.
- You're right, but I think there are some other benefits to doing away with the chain. I have an E-mountain bike and between chain stretch, chain damage, and mud I go through 2 chains per season plus a couple trail-side repairs. Also, no chain means you can optimize pedal speed/torque for each individual rider, and keep it in the ideal range all the time regardless of bike speed. Essentially it offers a much wider power band than gears and a chain. You could also optimize crank length for clearance instead of torque. The front chainring is also a big point of contact on mountain bikes, removing that could improve clearance with the right design. I'd also be interested in the regenerative braking - if I go on an Enduro ride I'm cooking my brakes on much of the downhill, regen could save those and recharge the battery at the same time. Maybe regen could even lead to a smaller battery and save some weight.
  Sure there are disadvantages - weight, complexity, efficiency, probably others too. I think with time those will improve though and this just might be a viable setup for certain use cases.
  
  I do see your points, where the chain itself is the cause of inconvenience or failure scenarios. Since the conventional bicycle is almost the textbook definition of minimal design, there are -- and will always ever be -- tradeoffs to make, and I concede that efficiency isn't always everyone's top priority for their bicycle.
  While I cannot discount that this chainless system would ameliorate the situations you described, I can offer some alternatives which can or already do exist today, that could probably be explored and improved over what this chainless system delivers.
  chain stretch, chain damage, and mud I go through 2 chains per season plus a couple trail-side repairs
  The front chainring is also a big point of contact on mountain bikes, removing that could improve clearance with the right design
  The older style of shaft drives in lieu of a chain could be maintenance free, and damage resistant. Efficiency is lower, and roadside repair is much harder, but efficiency is already lowered when in messy terrain, and if it's fully sealed, it might last a very long time anyway. Reviving this concept is something I could reasonably see.
  offers a much wider power band than gears and a chain
  Having discrete gear ratios will indeed always be a limiting factor when dealing with variable speeds, but there already exists a CVT (continuous variable transmission) for bicycles, where torque and speed can be traded in non-stairstep fashion. That said, no one makes a CVT with a built in ebike motor..... yet.
  You could also optimize crank length for clearance instead of torque
  I think I understand what you mean here, in that cranks today draw a larger circle to accommodate human physiology, but that also increases the risk of a pedal striking the road, or rocks adjacent to a trail. But I don't see how this chainless system can change the crank circle diameter on-the-fly. And I don't envision people wanting that very often, unless they want small diameter on trails and then want to bike home on the roads by switching to a large diameter.
  regenerative braking
  I think this already exists for ebikes: https://radpowerbikes.zendesk.com/hc/en-us/articles/360045171734-Riding-Rad-with-regenerative-braking
  I want to be clear: I'm not trying to shoot down the idea of chainless systems out-of-hand. But rather, these other solutions to your scenarios are more grounded in existing technology, or are waiting to be further refined before mass adoption, and likely will cost a lot less.
- Kinda crazy how many different things people have come up with but nothing has beat the chain drive.
  Gotta say, a belt drive with an IGH sounds like a nice commuter though.
- You write well.
- Good start, but you haven't factored in the multiplicative % losses from converting the stored electricity from the battery back into locomotion.
  This is the bike you only have to pedal 5 km, to travel 3.
  
  I left out a discussion on the mechanical-electrical-mechanical conversion losses because I wanted to focus on just the chain itself. My argument being: if a chain can do 97%, how on earth will a chainless system do better? Answer: it can't, not for the commonplace bike or ebike.
  But you're absolutely right that the double conversion loss must be horrific. Even EVs have contended with a similar choice before and today's hybrids do tend to be parallel hybrids.
  Locomotives are, I think, the only widespread application where the benefits outweigh the costs, bevause the cost of a behemoth transmission for a diesel locomotive would be prohibitive to build. Hence, diesel electric locomotives.

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