A line art schematic of a bicycle CVT drive. Two large green circles at the bottom have the text "1. Increases speed" where the crank arm would enter the system. A series of cam arms highlighted in red say "2. Converts from rotary to reciprocating motion." Finally, a blue highlighted bearing says "3. Converts from reciprocating back to rotary motion."

A Look Inside Bicycle Gearboxes

March 2, 2023 by Navarre Bartz 23 Comments

While bicycle gearboxes date back to at least the 1920s, they’re relatively unseen in bike racing. One exception is Honda’s race-winning mid-drive gearboxes, and [Alee Denham] gives us a look at what makes these unique drives tick.

Honda has developed three generations of bicycle gearbox as part of their company’s R&D efforts, but none have ever been released as a commercial product. Designed as a way for their engineers to stretch their mental muscles, the gearboxes were only used in bike races and seen at a few trade shows. In 2004, the third gen “derailleur in a box” led to the first gearbox victory in the Downhill World Cup Circuit.

The third gen gearbox differs significantly from the CVT drivetrains in the first and second generation gearboxes, but it is unclear why Honda abandoned the CVT. [Denham] has a nice animation detailing the inner workings of these CVTs based on information from the original patents for these rarely seen gearboxes.

Derailleurs remain the primary drivetrain in racing due to their lighter weight and higher overall efficiency. While still expensive, the decreased maintenance of gearbox drivetrains make a lot of sense for more mundane cycling tasks like commuting or hauling cargo, but only time will tell if the derailleur can be supplanted on the track and trail.

For more on bicycle drivetrains, check out this chainless digital drivetrain or the pros and cons of e-bike conversions.

Continue reading “A Look Inside Bicycle Gearboxes” →

Adding Electronic Shifter Functionality To Bicycle Derailleur

January 26, 2023 by Maya Posch 19 Comments

For the overwhelming majority of bicycles out there that feature multiple gears, switching between these is done purely mechanically, with a cable. Generally this uses a derailleur, which forms part of the gear switching and chain tensioning mechanism. As a mechanical system, it’s reliable when well maintained, but tuning it can be a real hassle. This is where an electronic shifter should be able to provide faster, more reliable and quieter shifting, and is also where [Jesse DeWald]’s electronic shifting project begins.

As [Jesse] points out in the introductory article on electronic shifting, it’s not a new concept, with everyone from Shimano (Di2) to Archer and others coming up with their own version. Some of these require replacing the existing derailleur, while others should allow for non-destructive modification. What [Jesse] did not find among this constellation of options was a version that’d work with existing derailleurs, did not require destructive modifications and have a long battery life.

[Jesse]’s design omits the servo present in Archer’s design, and uses the existing derailleur spring, with the reasoning explained in a nice spring physics refresher. Instead a stepper is used along with a matched balancer spring that in testing managed over 3 months of standby time with a 3,700 mAh Li-ion battery and thousands of shifts. At the core of the system is an Arduino Pro Mini board, the code for which is available along with the design plans.

The project is not done at this point, of course, with a whole range of improvements still to be added, including a case, so that the shifter can be used outside in the rain.

Mix And Match Parts To Build A Better Mountain Bike Derailleur

August 13, 2019 by Lewin Day 4 Comments

Mountain bikers take their sport seriously, and put their bikes through all manner of punishment in the course of a ride. This has given rise to a wide range of specialist equipment, such as suspension, disc brakes and even clutch derailleurs, which help reduce chain slap when riding over rough terrain. However, these specialist derailleurs aren’t available for all applications, so sometimes you’ve gotta hack together your own.

Shimano clutch derailleurs are only really available for 10-speed rear cassettes and up, due to a change in derailleur ratio compared to the earlier 6 to 9 speed cassettes. Using a derailleur designed for 10-speed operation on a rear cassette with fewer gears won’t shift properly.

[SzurkeEg] was inspired by earlier work, and realised that by combining parts from several generations of Shimano hardware, it was possible to build a working clutch derailleur for 6 to 9 speed rear cassettes. The main parallelogram is what handles the positioning of the derailleur, and is sourced from a 9-speed part to get the gear indexes correct.The rest of the parts are sourced from later models with the clutch feature built in.

It’s a smart mechanical hack, and one that isn’t necessarily the most intuitive. But by having a go, and seeing what’s possible, now a whole generation of mountain bikes can tear up the trail like never before. We’ve seen Shimano gear hacked before, too. Video below the break. Continue reading “Mix And Match Parts To Build A Better Mountain Bike Derailleur” →

Electronic Bike Derailleur

June 6, 2012 by Brian Benchoff 38 Comments

[Nabil] sent in an awesome electronic bicycle derailleur. Now, instead of pulling a steel cable with a shifting mechanism, [Nabil] can change gears electronically. As a bonus, the derailleur can be controlled by a small bicycle computer, so he’s always in the right gear.

The new electronic derailleur is controlled by a pair of servos with push buttons in the handle bar. This allows [Nabil] to automatically trim his chain, completely eliminating chain rub.

This electronic shifter is part of [Nabil]’s much large bike computer project. In addition to electronic control of what gear the bike is in, [Nabil] will be adding a GPS, accelerometer, an altimeter and a heart rate monitor and pulse ox meter. That’s an impressive bit of kit, and we cant wait to see the entire project finished. You can pick up the current version of the design over on GitHub and follow all the updates on [Nabil]’s blog.