Electronic Bike Derailleur

[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.

38 thoughts on “Electronic Bike Derailleur

      1. one question – why did you use #3 and #4 screws for attaching things to the derailleur? I guarantee you those are metric screws and you’re botching the threads.

  1. I’m guessing it’s geared down using threaded rod and takes a while to shift but neat solution. There are commercial units available for this (Shimano Di2) which does everything including self-indexing using sensors to find the gears but IIRC it was somewhere in the £1k region for the setup.

    1. There is also Shimano Nexus SG-8R series which is a 300% ratio 8 speed electrically shifted hub gear. I hear they weigh close to 2kg before the wheel is built up though. The shifter is part of their cycle computer and has auto and manual modes. It is powered by a hub dynamo.

  2. I like the idea. I’m fairly certain this addon would chew up chains fairly quickly. When you shift on a bike you generally let off on the torque as you shift, it’s a natural thing humans do as they don’t want to hear metal grind down into metal teeth. I’d say unless you can time the shifting to coincide with when the pedals are at minimum torque (seems possible) and finish before the rider beings to apply new force, this would be murderous on chains to use in hilly areas.

      1. Uhh, fellows, he’s talking about stopping pedaling. draeath, “let up on the torque” means reduce the forcefulness of pedaling to reduce stress during the shift event, not stopping altogether which would obviously not work as you said. The point is that if this thing were auto-shifting you wouldn’t know to go easy on it during the shift. “Manual” push-button electric shifting should pose no issue though.

        Cool project! I think I might start researching servo options…

  3. I’ve been wanting to do this for years.. and I think about it each time I ride. Having to reach Allllll The Wayyyy Dowwwwnnnnnn to my downtube each time I shift is a great reminder and motivator! :-/

    I knew I wasn’t the only one thinking about this.

    I still use friction shifting, and don’t believe in all the junk, expense and related lock-in system BS involved in modern plastic versions. It seems like expensive throw-away tech. Good luck getting parts in a few years.

    One requirement I have had is that the manual shifting continues to work as a fall back, even without power.

    1. > One requirement I have had is that the manual shifting continues to work as a fall back, even without power.
      This would be a nice feature. Might be possible if the servo moves the cable instead of the derailleur directly.

      1. For it to move the cable, it would have to still have the spring in the parallelogram mech, AKA, it won’t work. That servo won’t be able to win in a strength competition against that spring, it is really strong, which is why he removed it.

  4. First off: there’s no chain rub on the rear cassette on any modern bike with indexed shifting. Chain rub happens with the front derailleur, not the rear.

    Second: it’s not hard to ‘imagine’ anything about this: Navic made a system back in 1992. Shimano’s Di2 has been out for several years on their high end system. Both *trimmed* the *front* automatically to avoid rub on the front cage.

    I don’t think either system auto-shifted; that’s not a feature the high-end road bike market wants, really.

    Jeremy: Modern cassette and chain designs can handle shifting under considerable power.

  5. Now that’s my kind of bike hack. I’ve always wanted to do this too, I’m impressed a hobby servo has the guts (even with spring removed). I wonder how the servo’s gearbox will hold up in the long run to the vibration and higher tension while shifting under load.

    1. Bikes had automatic shifters nearly 100 years ago, it changed gears based on the tension on the chain (and/or a governor?). A few people have taken a crack at it over the years, eg Shimano as mentioned, but they’re too expensive.

      I always thought CVT (continuous variable transmission) would be amusing to put on a bicycle. The concept is simple; it’s just a couple of split pulleys; but efficiency is a bit low compared to chains apparently.

      Hubs gears were making a bit of comeback, they’d be a better setup combined with an electric motor.

      1. The one I was thinking about was around the time derailleurs were invented, say 1920’s. I’ve no idea how it actually worked.

        Someone started making Duomatics again a few years back. Haven’t heard anything lately, probably like the NuVinci it’s too expensive and not any better than what we’re already got.

        I guess it’s greasy chain & cogs for a while then.

  6. I work at a Bicycle Part distributor, and I know we just got a new product in this year, a Wireless Rear and Front Derailleur. I should take a closer look at those, see what sort of mechanics are behind it.

  7. Awesome! I’ve been planning on doing EXACTLY this for my old mountain bike I want to convert to an exercise bike! Now I’ve got some solid leads on what to do. :D

    I envisioned computer-controlled shifting as a way to make sure the bike ends up back in a lower gear if I stop, and to be able to make variable-resistance exercise programs!

      1. You’d be surprised. I didn’t think so either, but I see tons of people making their own carbon frames, making rims out of nothing but an extrusion, homemade derailleurs, hubs, stems, seatposts, etc. The only thing I haven’t seen are chains and spokes. I guess cuz they are cheap.

  8. I’d be more interested in this on an internal gear hub… but I’m very much into those over the noodle-doodle idiotic “jumping a chain from gear to gear in mid-air by applying sheering force” — which with my engineering background is just as stupid a design concept as nylon bushings on something spinning 15K RPM (thanks Seagate) or making every door in a public building open inwards.

    De-railers are (or should) be cheap, lightweight, and that’s the only two legitimate reasons to use them. Decent 5 speed internal gives you the same range of ratios, and really the only reason to need more than 5 speeds is bragging rights… since beyond a certain point it should be about range of gearing, not number of gears.

    As it is I can’t ride any de-railer more than 100 yards without dropping the chain when it comes time to shift, I don’t even want to think about having one of those try to shift when I’m not ready for it… Not certain I’d even consider that ridable with an internal since that sudden change when you don’t expect it — particularly if it downshifts while riding — could really mess you up… well, unless you’re one of the hardcore nuts with the clips.

    Though it would be very interesting to see on a CVT.

  9. I recently read that electric shifting has won the tour de france for the last 3 years.

    If you search you can see the latest tech from shimano and campi. Amazing carbon fibre stuff.

    Me, I just want a simple servo solution for my old friction shifters.

    Regarding the requirement that manual shifting still be available – I suppose a fine compromise is the ability to manually set a specific gear. That seems like a perfectly adequate limp-home mode.

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