Chainless “Digital Drive” Bikes Use Electric Power Transmission Instead

We’re all familiar with how regular bikes work, with the pedals connected to the rear wheel via a simple chain drive. This setup is lightweight, cheap, and highly efficient. It’s not the only way to drive a bike though, and there’s plenty of buzz around the concept of “digital drive” bikes.

Look, ma – no chains!

These drivetrains rely on electrical methods to transfer power in place of mechanical. The pedals are used to turn an electric generator, with power then sent to an electric motor which drives the rear wheel. The concept may sound overly complicated, but it does offer some benefits. The generator can change its operation to keep the rider pedalling at their most efficient, consistent rate. There would also be no chain to fall off, get snagged on clothing, or require regular maintenance.

It would make integrating regenerative braking possible, too, allowing the bike to harvest energy when going downhill too. This could be achieved with a storage battery or supercapacitor. As a bonus, it would be very easy to integrate power assist for the rider when tackling tough hills, for example. The lack of requirement for direct mechanical power transfer also means that there’s far more flexibility to design a bike with interesting geometry.

Such drive systems do give up some efficiency, however. All the power conversions between mechanical and electrical energy mean that a “digital drive” would likely only be 58% efficient. This compares poorly to the roughly 95% efficiency of power transfer in regular mechanically-driven bikes. There’s also a weight penalty, too.

Presnetly, there’s only one “digital drive” bike on the market – known as the Mando Footloose. It’s a swooping, folding, futuristic design, that has some feel issues when it comes to pedalling. And, given the added complexity and expense of these systems, it’s unlikely regular bikes or e-bikes are going away any time soon. Regardless, it’s fun to think about the potential for other drivetrain concepts to change the way we cycle. Video after the break.

[Thanks to Keith Olson for the tip!]

140 thoughts on “Chainless “Digital Drive” Bikes Use Electric Power Transmission Instead

      1. I met a guy about 30 years ago who had an electric generator built in to a motorcycle rear shock. He was very excited about it as it would require a much smaller and lighter alternator to be fitted.
        Never to be seen/heard of again.

        1. The tech makes sense, fundamentally.

          The shock absorber needs to dissipate energy. Controlling the damper rate is a favored method of “active” suspension, so one just controls the regeneration rate.

          Oh, and it could fundamentally be a fully active system, applying a preload force to the springs to temporarily raise/lower suspension elements to climb over obstacles.

    1. frictional losses aside, yep, really ignorant idea. Almost as inspired as building steep sloped hills next to wind turbines, installing railroad tracks on them, and then using excess generated electric power to drive the railroad locomotives up the slope, then when the wind dies down, the weight of the locomotive turns the traction motors to generates power to feed back into the grid. YEAH someone actually proposed that. So far, these “green energy” ideas are pretty sketchy. The inputs for battery and turbine tech (lithium, cobalt, nickel, graphite. Copper, steel, plastic, and neodymium magnets) are for the most part mined, and to a large degree this mining is done by China. Not a great track record of ecology there. Its impossible for an electric wind turbine to ever pay for itself based on the carbon costs in its production. Thankfully the masses are ignorant to engineering, mining, and economics, one thing they do well is complain, after getting all their information from Mass media.

      1. The energy/CO2 payback period for a wind turbine is on the order of 5 months (less than hydro or solar) and a modern wind turbine will produce 50 times more energy than is consumed in production.

        Seems to me like you’re the one making ignorant complaints here. What is your alternative to mass media, viral Facebook posts? Because it certainly doesn’t seem to be anything factual.

        1. A good investigator reads the references. The GHG payback period assessment is smoke and mirrors.

          Those references for your linked paper focus on net electrical consumption, not GHG emissions (yes, you allowed for that in your “energy/CO2 payback” term). That’s not the same for net electrical consumption, and the referenced articles shortcut the work by presuming GHG emissions are adequately proxied by GHG emission for electrical production, or they explicitly avoid trying to analyze GHG emission due to wind turbine production and maintenance. E.g., “The CO2 emissions…we’re calculated…from…energy requirement data. …. In this analysis, the CO2 emission factor for electricity was based on the average of the U.S. electrical mix of 1996 as shown in Appendix A.“ (White S.; Kulcinski G.. )

          Average GHG production per unit electrical energy is a poor proxy, as few mines use electrical trucks, loaders, and mills.

          1. When all energy production does not emit GHGs, then the only consideration is about of power produced versus amount consumed in construction, maintenance and transmission. If less power is produced than consumed, economics will ensure that wind power is not commercially viable. As ICEs are much less efficient than electric power trains, it is obvious that wind power is energetically positive.

          2. agreed! devil is in the fine print. plus wind power isa both intermittent and subject to “goldilocks” windspeed constraints. Wait until they realize that alcohol fuel is the answer. all the government setaside acres (farmers paid not to grow crops) switched to biofuel production would create less pollution and env friendly vehicles. the “power wheels generation” forgot that dad switched batteries so they could drive all day.

          1. In no world would someone consider wood a good material for a wind turbine producing electricity. Hell, totally useless anywhere with termites, unless you pressure treat the wood with some hard hitting pesticides. Alas, then you have created tons of hazardous waste and excluded your “ecological wood” turbine from any ground water basins. Just because something exists doesnt mean it should.

          2. Does your power wheels car work at 10 below zero? Also where is your data to support your claims? Btw – whats your mechanical/engineering background? I had 10 years in powertrain transportation engineering.

        1. only way for wid to work is individual power generation. otherwise way too much transmission losses. plus home genersated power can be better adapted to individual needs and doesnt require massive infrastructure or corporations. only reason “big power” has the wind and solaris to negate the cost of buyback from customers. they pay out at their own at fractional cost per kwh generation rate. giveaway is do you see any substations near wind farms? if not then no HV AC being transmitted, just power lines to start the windmills. even 440VAC cant transmit too far without losses. need 72k or 144k and for that you need powerlines and substations. whole green energy is a sham.

      2. Generally the idea to use gravitational potential energy as a storage medium is about smoothing output rather more than acting as a 2 week UPS, the train up a hill approach isn’t a bad idea in the right place… It has got merits entirely because it is so very very simple to build, needs no exotic/rarer elements that can be better used elsewhere and has material and/or environmental costs that rather closely approach nill when you compare it to any other energy store – its just a bit of steel and copper with perhaps a few permanent rare earth magnets draped over a hill.

        Its even better if that train is also doing useful work – for instance a mine in AUS has a railway to carry its product downhill to the dock and the empty trains return is powered entirely by the energy captured from controlling that trains speed on the descent. Similar concepts can be done with systems meant to be a gravity ‘battery’ – lots of things folks want shifted up or down with no great urgency so a pause in progress to provide power rather than consume it is fine. Just don’t expect this gravity store to power an entire nation for an unrealistic length of time, unless it is also unrealistically large…

        You want to pick fault with the wind turbine you went at entirely the wrong thing – the fault you can actually back up with proof is the number of ‘spent’ turbine blades being generated. Many of them are just older smaller blades with life left in them that got replaced with bigger ones for more generation capacity – easier to make existing turbine bigger than get permission for a new location. But they do still have a limited lifespan, the larger the blade the shorter that life (as it stands) and at EOL nothing much can be done with them (yet anyway).

        As for sourcing stuff from China or any other nation with poor practices, that has nothing to do with green energy, its a rather close to universal problem with nearly everything made and used entirely because it is cheap to get whatever it is from those places.

        1. Gravitational storage is actually a really good thing and is commonly done where I am (Scotland) using pumped hydro. So when there is excess power it pumps water up to a reservoir and then when extra power is needed they let the water out and it generates power like a dam.

          It is a pretty decent system with the only real disadvantage being the amount of land needed for the reservoirs.

        2. The train is not “convenient”. You need massive store of “heavy material” at the top or bottom to make a reasonable impact. If you use “water” as a “heavy material” to haul up and down a hill, THEN you can suddenly store square km’s of the stuff on the top and bottom stations. (bottom stations much less, agreed). (I found 30 places with more than 1km^3 of water reservoir on the wiki page about such large installations)

          Even a modest 30m deep 500mx500m lake has a tremendous capacity compared to a bunch of train cars.

          1. And that 30m deep rather giant hole in the ground if it doesn’t happen to already exist will cost orders of magnitude more to dig than heaps of rail based systems…

            Water as a mass is common enough and can be a great idea, but you only get really large scale reservoirs if the geography happens to be obliging, or very rarely because you desperately need that water supply for other things like drinking. As that makes the expense of the tiny steel boxes on stilts or deep holes in the ground to put all this water in is worth it for other reasons.

            Where large enough stretches of hills or even full on mountains you can smooth out and/or zig zag up enough are almost universally available – its convenient in the sense it can be pretty damn cheap to build near enough ANYWHERE. Still won’t be the right solution for EVERYWHERE, as some places will have natural advantages or other man made infrastructure you can use, but even in those places its likely cheap enough AND being a train can be useful bulk material or passenger transport at the same time!

            With gravity store even the most giant pumped hydro dam you are still not talking huge output for huge duration – the pond is only ever so big, and so far above the generator, it can be a rather substantial store but it generally still isn’t more than grid smoothing power output.

            Also most hydro locations end up needing to let water out at all times to maintain the output river – while you can increase and decrease the flow somewhat to match power demand you really can’t shut the river down when its not required, or flood it out just to keep the lights on. Dealing with a train on a track is rather simpler to operate being an entirely man made system.

          2. why not just use hydroelectric to begin with? we have dams existing on Mississippi river that “could” generate electricity but environmentalists claim it would kill fish… the Asian carp!!!

      3. People don’t seem to realise how “ungreen” some of these “green” energy solutions are.

        A good example is wind turbines, the blades eventually need replaced and they aren’t easy to recycle since they are generally made of fibreglass. Then you also need to consider the impact of installing them, they require large machinery to install and it generally isn’t electric, even worse if it is an offshore wind farm, then they need a huge vessel that is large and study enough to install the wind turbines, they also aren’t electric powered so they need to burn a lot of fossil fuels to install these green solutions. Then there is the manufacture of them, they aren’t designed using sustainable or environmentally friendly materials, hence we are now ending up with fields full of discarded turbine blades.

        All that is swept under the rug by politicians and green energy advocates though.

        That is before we get into the issues with this method of generating power and how it is unreliable and isn’t really suitable for a base load. It is also much faster and cheaper to reduce a wind farms production than it is to with a nuclear or coal plant, so when there is too much power it is the unreliable and quick green power that is turned off and the coal and nuclear plants that generate the needed power.

        1. Other solutions are equally bad or worse, with similar problems at ELL, and may even produce GHGs (new gas/call power stations). No solution is perfect. I’m sure somebody will come up with a good use for recycling wind turbine blades.

    1. I was thinking the exact same, and then I went what if it was marketed as a super inefficient method of transport for people who wanted to drop from 25+% body fat down to 2%body fat. For a start the image above would need to go, unless it is the “after” photo.

    1. Indeed… what kind of electrickery is this?
      Reminds me of a pair of headphones I had years ago, “digital” headphones — but still used a conventional 3.5mm TRS connector, connected to very much analogue 32ohm speakers.

    2. Yup. This is my main gripe with the idea as well.

      People calling things “digital” just because it uses electricity is frankly abhorrent and misinformed.

      Though, there is also a slew of people who regard anything not electric as “analog”. Something that likewise is factually incorrect. (a mechanical calculator is very much digital, same for a lot of other mechanisms.)

      Digital is a system with discrete states. Typically on/off, but tri-state and even decimal is still digital.

      Analog is something that doesn’t have discrete states from a practical standpoint. (even here one can likely still argue that the universe is quantized at some level.)

    3. All bldc motor controllers use pwm drives so yes it is digital
      It’s also likely that it uses a buck/boost controller to charge the battery, also digital
      The whole lot will be controlled by a digital MCU so I do believe digital is accurate but I’m this context it sure feels like buzz word marketing just the same

      1. “Analog” is defined as “of, relating to, or being a mechanism or device in which information is represented by continuously variable physical quantities”.

        PWM isn’t “digital” if the pulse width is continuously variable without discrete steps. Likewise, the buck/boost converter typically uses analog feedback to control the switch in a continuously variable fashion. There’s no A/D conversion or a micro-controller in sight, just an oscillator and an op-amp that compares two voltages to generate a continuously variable PWM waveform.

        1. Pwm is digital as the output has 0 & 1 as discrete levels, it’s also analog
          The 555 timer is analog and digital for the same reasons
          To be pedantic, these e bikes are MCU controlled so truly digital but the use of the word in this instance is all about marketing, not technology

    4. Same here! I’m surprised they didn’t call it “HD”, though maybe we’re past that buzzword’s prime.

      But it’s still worse than calling something “AI” when it’s just a damn program doing what its programmer programmed it to do. I’m not nearly as much against using the term “machine learning,” but to call a damn program “artificial intelligence” is just insulting to actual intelligence.

        1. “_nik” was the early 60’s from Sputnik. If there was one word for superlatives from the 70’s it might have been “Hi-Fi”. The other common word I heard in my childhood was “Peace” to go with all the free love. One common combo was “Peace-nik”. Another one is “Econo” from the early 70’s oil crisis.

  1. We laugh at this the same way cyclists laugh at the dandy horse, but it’s still a proof of concept. What would happen if it used room temperature superconductors to store energy at 100 per cent efficency. Would we be laughing then.

    1. Probably, because then you’d still have a bicycle that is comparable in efficiency to a chain drive except it would cost a quarter of a million dollars and probably have some exotic heavy metal in it that emits cancer rays and was mined by thousands of slaves or something.
      Some designs are already optimal. The efficiency of a bicycle will probably not improve more than the slimmest margins. 95% efficiency is ludicrously good for a drive train of any kind.

    2. I posted this in the wrong place, so here we go again:

      You’re not wrong – but hilariously misled.

      A proof of concept proves the basic physical feasibility. Energy storage isn’t the problem here – it’s electromechanical conversion efficiency.

      If your proof of concept for a mobile device requires building something that physicists since the first electric motor have not been able to do in a lab setting, it’s a proof that a concept isn’t viable. Full stop – just as there’s proof of concept rocket bicycles, there’s good physical reason this isn’t what should be between a human driver and the wheels.

      (Note that this in principle an excellent concept – diesel locomotives typically are diesel-electric locomotives for the article-mentioned reasons: being able to run an engine at a sensible rpm while being able to flexibly adjust torque at different speeds. Just that low-RPM diesel train engines are a different kind of power source than a human, and that the weight/size/cost/complexity tradeoff for bikes and heavy duty trains is kinda different. Slightly.)

    3. Superconductors cannot store much energy without more mass. The problem here, is the inefficiency of the conversions to/from mechanical energy compared to mechanical transmission, not energy storage.

  2. Honestly, I did this for my son. He was 3 at the time, but I bought a pedal bike for him. Turns out, he didn’t have the leg energy to actually pedal the car on anything other than slick concrete. So I converted it to electric by throwing a hacked hoverboard into it, 3D printing hub wheels to match the pedal car tires, and then hooking the pedals up to an encoder and letting that dictate his speed. He still pedals, so I’m happy that he’s still getting leg exercise, and he’s happy that he can zoom across the grass yard and focus on steering rather than pushing as hard as he can. You can find the parts I made for it on printables if you search for “pedal car”. Still working on a write-up on what I did.

      1. “Go to the big online bookstore and search for ‘cadence sensor hub motor’, then delete the bike chain” – not very exciting reading.

        The parts are out there, convenient, and awesome.

        I personally used a TSDZ02 kit featured on a previous HaD article, to great success. I find the torque sensing throttle to be far more natural than a cadence sensor, but it’s a higher end unit.

  3. Although the engineer in me cringes, it’s not that bad of an idea.

    A massive percentage of my electric bike sales are to older people who still want to ride around with others. Their friends often can go farther and faster. They also want to get exercise. They have no clue how or when to maintenance a bike and their anxiety stops them from riding completely. They just want the ‘Apple’ version of biking. They don’t care about efficiency since price isn’t an issue (more battery).

    I don’t see any reason why the size and weight is so massive though. There’s no reason the generator is that big or efficiency only 58% either.

    After ~2000 miles dealing with my own cheap $400 DIY electric daily commuter (exercise bike that gets me to work), the chain became too much. I was going to spend four figures on a nicer ebike. Then I realized my 1200W bike can already make it to work going upwards of 35MPH without me pedaling AT ALL. My contribution is pathetic. So I just removed the chain drive, used the thumb throttle to control the motor (instead of PAS) and replaced my crank cog with a disk brake. A shift lever adjusts pedal resistance now. Now my commute is so relaxing. No more thinking about shifting, awkward PAS starts/stops at intersections, searching for the correct gear, not having a high-end gear so my legs have to move way too fast, waiting for the dame thing to finally shift in low gear when loaded, grease on pants, pant getting caught, over-shifts, and chain/shifter maintenance, delicate frogs breaking, etc etc.

    Get the weight down and efficiency above 85% and it would definitely sell.

    1. At 1200W and 35mph, you no longer have a bicycle, you have an electrical motorbike.

      In my country, bicycles are limited to 250W to not be able to be used like motorbikes, because the rules aren’t the same for motorbikes. This limit is theoretical, but when you are limited to 250W, the efforts with the pedals are important…

      What is your battery capacity ? Just like old gasoline-powered bikes kept the pedals just in case, even if you don’t pedal, it may be useful, if the battery is totally discharged.

      IMO, these “digital” bikes are stupid, because it’s a bad middle ground between a standard bicycle and an electric bicycle. Even in assisted electrical bicycles, they still keep the chain drive to be able to use a smaller motor for the same total power.

      1. In your country you might have a “motorbike”. In their jurisdiction, they may just have an electric bike. (Also, I’ve never seen a motorcycle that can’t go faster than 35mph. Maybe a scooter or a moped). Why are you correcting or trying to affix his definitions to match yours, when we all know different jurisdictions define things differently? Why not just accept the definition given?

        1. I’ll bite. We are all here speaking English, even though for many of us it’s not our native language – why? Because having a common language allows us to talk.

          When talking about eBikes, if one person is thinking about something that could reasonable called a bicycle (i.e. it has reasonable power and weight, and needs to be pedaled), while another person is imagining something as powerful as a gas powered moped or motorcycle that has a throttle and weighs a ton then the term “eBike” becomes completely meaningless.

          Laws are different in different countries of course, but in most countries, an “eBike” is something you pedal, and the assist ratio of total wattage is limited.

          A 1200 watt machine that doesn’t need to be pedaled indeed is regulated as a “motor vehicle” (usually moped) in most places because at that point, that’s what it is for practical purposes.

          This King if “it has an electric motor, so it’s an eBike” thinking is why people keep getting hurt in things like Sir Ron’s. “It’s just an eBike”, they think, of to their doom.

          I suppose the silliness will stop one mainstream motorcycle go electric, as probably nobody would call a 5000 watt electric Ducati that weighed 200lbs an “eBike”.

          It’s true that laws differ by county, and in particular the US has a complex and unusual system, but it makes sense in an international site that we agree with the definition used in the majority of countries for ease of communication.

          1. Another well measured and eloquent reply. Thanks!!!
            (I’m trying to personally thank those that take time to address concerns well instead of…. the other thing )Cheers

    2. 1) slow speed small generators/motors are very bad efficiency wise. 58% seems pretty good for each end, about 34% total. Roller chains are around 98% though.
      a) To get to your mentioned 85%, both ends would need to be 92% efficient. large industrial motors are 94%, VFDs are 97%, which is only 91%.
      2) As for maintenance, seems like there is opening for the LBS to provide a 4x per year “service” for the ebike they sold, including reminder calls.
      3) Your chainless ebike, is an electric scooter and not a bike. Please only use it on the road and make sure you have turn signals and such as required by your local laws. It probably was already a scooter and not an e-bike because of the throttle depending on where you are.

      TBH, chain maintenance is pretty easy, wash once a week, lube with light machine oil or a specific chain lube. Use a $5 chain checker once a month to see if you need a new one. Or you can do nothing and just replace them every year. Either that or just bring it to the LBS at the start, middle, and end of the biking season for a tune up.

    3. Commercial EV powertrain efficiencies are regularly (advertised) in the low-mid 90% range. That’s for DC-AC, so for AC-DC-AC you would need to square the ratio. For example, 0.92^2=85%, right what you mentioned. Of course, that efficiency will be load and speed dependent, but the operating range of a bike is narrow enough that I think that’s achievable.

      I think that, more than electrical efficiency, is that now you have two motors/generators of weight. I still think it’s a perfectly reasonable concept.

      Or, like you said, get a healthy battery and the efficiency is kinda moot.

    4. Just get them a bike with hub gears. Simple enough, and you only need to change the chain when it stretches so much it starts to skip, which for an elderly person would take forever.

  4. you guys are missing it remember the comment of adding a battery or super cap?? regeneritive braking do those things mean anything too ya when you store up the extra 31 to 40% from braking you will go 100% of the distance on 25%% of effort….

  5. The slide @ 9:59 is wrong.

    In particular, his “mid drive” diagram is basically saying that a mid drive (80% * 93% = 74%) is less efficient than a hub motor (80%), which is patently not true. In normal use, the hub motor will get trounced by a mid drive in terms of miles/kwh.

    The peak efficiency of both a mid drive and hub might be 80%, but a mid drive is going to be able to operate in that zone over a much wider range of speeds / inclinations. So, in practice, your hub motor might be more like 50% efficient over the entire ride.

    1. Okay so all we need to do is put a mid drive motor where the generator is… But since we are using a mid drive, we need a chain to transfer the power to the rear wheel. Since the motor and generator can’t be in the same place, just replace them with an axel .. voilla!

    2. mid drive is more efficient due to better gearing via the derailleur however a 2 speed hub motor would manage quite well, also it depends on the desired cruise speed of the design
      This serial hybrid design would probably do ok if the generator is properly optimized
      It also benefits from being able optimize the pedaling speed to the rider rather than the road speed, allowing more comfortable riding
      the efficiency figures are poor

      1. Yeah but like it’s soo bad it’s not interesting what are you talking about. Like some random infomercial stuff is “weird and interesting” but that’s only if you look at it from the most surface level view otherwise it’s just a scam.

  6. It would be interesting to see how the motor/generator efficiency compares with that of a pair of stepper motors. Especially if they had a bit of a boost from a flux redirection design using some neodymium magnets.
    Even at a fairly low rpm, a standard stepper motor, as you’d pull from a printer or such, can put out around 50V usually with enough current to make your fingers tingle and they’ll happily drive each other as you’d expect from a regular dc motor, but you get a fair amount of torque, all be it possibly with a little more weight.

    1. A given stepper motor will never be more efficient than a similarly sized PMSM or BLDC motor. Fundamentally, they are always trying to drive current along the d-axis. If they have torque applied and rotate a bit, some of that current appears along the q-axis and creates counter torque. For situations where you want high efficiency power transfer, you would be better off putting all that current along the q-axis to begin with.

      Note: if you’re not familiar with the DQ0 frame, Wikipedia has a good explanation.

  7. Even though, for most users, this is a loss over bikes Classic™, it does offer interesting possibilities, such as far simpler (and possible) folding bikes, no need at all to have a fixed distance between pedals and wheel hub, and battery-electric bikes that alow the rider to charge and cogenerate even when not needed (going wind ahead or downhill), and I find it brave they not only designed but also produced and marketed it.
    Time will tell if this is the first in a new design paradigm or (highly probably) an idea never heard from again.

    I don’t understand the deep negativity in the comments for a site dedicated to novel use and applications of ideas.

    1. While its clearly less efficient than direct drive chain, there are aspects not considered, such as optimal rider comfort by controlling the pedal torque & rpm independently of the drive motor or the gains possible by simply using improved motor/gearing arrangement for the genset and drive motor

  8. Here’s a bicycle concept I came up with years ago. Air-hydraulic. Replace the pedal crank with pedals on a pair of longer levers. To those levers attach air cylinders so that pushing down and pulling up (shoe clip pedals required) compresses air into a pair of tanks. Inside each tank have a free floating piston that separates the air from the hydraulic fluid.

    As the rider pedals, air gets compressed into one of the tanks, pushing on the piston to force hydraulic fluid through a hydraulic motor. Meanwhile, the fluid coming back from the motor is flowing into the other tank, pushing the piston up and air out through a vent.

    When the pistons reach top and bottom, valves automatically flip to reverse the flows and switch which tank has an open or closed air vent. The valves and piping are arranged so the hydraulic fluid always flows through the motor the same way.

    There are some bikes using long levers and various systems to transfer the power to the rear wheel. The Bygen Hank apparently only made it to prototype stage. Confusingly they made a production model also called Hank, which is a short bike with conventional pedals directly driving the rear wheel.

    NuBike is apparently in production with a road version while a mountain version is “nearing production”. Its long pedal levers connect with a pair of rigid links to a disk on either end of the rear axle. Bikes of similar concept have been done before.

    Presisia Bikes in North Carolina has lever drive bikes for sale or rent.

    One I saw back in the early 90’s used a freewheel and sprocket on either side of the rear wheel and two short lengths of chain to drive it. IIRC the bottom/forward ends of the chain were connected to a cable that went around a horizontal pulley. I know I read about the bike in some magazine article and I did see one in person one time at a physical therapy gym. IIRC someone said it was great for knee surgery rehab since it didn’t require as much knee bending as a conventional bike.

    1. The Precisia uses a dual chain system but aside from that it’s very much not like the one from the 90’s. The Precisia looks like it’s put together in someone’s garage or small machine shop. The older one had cast or forged aluminum pedal levers and overall a more polished, conventional look.

  9. You’re not wrong – but hilariously misled.

    A proof of concept proves the basic physical feasibility. Energy storage isn’t the problem here – it’s electromechanical conversion efficiency.

    If your proof of concept for a mobile device requires building something that physicists since the first electric motor have not been able to do in a lab setting, it’s a proof that a concept isn’t viable.

  10. This article being here seems fine on simply on the basis of “look at this quirky bit of tech”. Is it a good idea? As a cyclist and an engineer I could without much hesitation say No and No.

    The truckload of negative comments being here even serves a purpose. We live in an age when powerful forces compete for whatever discretionary spending we have left, and in this marketing is king. Get the sale. Sell, sell, sell. Imagine someone who doesn’t know much about technology, or bikes, discovers that .. thing, and has nothing but ad copy to go on. They won’t realize that it’ll make riding on firm pavement feel like slogging across grass or sand, until they’ve tried it. At least with our collective dismissal posted here, someone who does a bit of research before buying stands a chance of avoiding the inevitable disappointment.

    1. I think you are correct, though I would say the concept isn’t entirely without merit – it is a good way to get the convenient to use ‘light e-motorbike’ where the battery does much (or even all) of the work in a form that is legal to ride without licenses in many places. So it might be actually useful…

      It might be a terrible idea from purely a cyclist or engineers perspective* but from a getting folks to take cheaper to run, more ecologically sound forms of transport AND get a little exercise in it could well be a winner. As to get the non-cyclist unfit individual to want to cycle it has to be possible for them to get where they want to go… Or to get the technically incompetent, don’t understand gears type folks on a bicycle with no parts they need to maintain or understand how to use… There is I think a niche for such a thing – it just isn’t for me or likely any of the readers here, as even if they choose to get a rather heavily electric assisted bicycle they would pick the engineers choice…

      *(I suspect it is, but it might actually be a lot more fun to ride – in which case many a cyclist might choose it despite being less efficient)

    2. Great question, is this a good idea or not? Compared to chain drive efficiency the consensus seems to be no. So what other better variations might this trigger? Like a recumbent bike without an 8′ chain and other reconfigured options? How about the less mobile person’s tricycle for getting groceries or other short excursions?

    1. wow, only 6000€ !! For this price (or a little more), I can get a new two-person electrical car with far more autonomy AND speed. The price is ridiculous, but the concept is good.

  11. I came up with this idea a couple weeks ago after finishing a 50 minute session on a trainer in erg mode and thinking “gee wiz. It sure would be nice to time trial with constant cadence.” I also dismissed the idea a couple weeks ago because I didn’t see a path to getting the overall efficiency much over 92 or 93%.

    I do think you can get the efficiency to that level, though. I time trial (and more generally just ride) at 40 to 50 Nm at the crank. That torque isn’t steady, so figure most of the losses happen at 70 to 100 Nm. A high end 100 Nm PMSM isn’t that crazy, but it’s going to be big to get the torque density – probably something with a diameter of ~30 cm and a mass of about 3 or 4 kg (based on some _really_ fuzzy extrapolation from motors I’ve worked with). A cool thing is that you’re not going to have meaningful iron losses because the current ripple will be really low from all the inductance and the fundamental frequency will be in the 10’s of Hz (even with a high pole count motor). The wheel side could use a similar motor and just shrink the wheel to lower torque requirements.

    The thing I’m not sure about is how efficient you can get the inverter. I haven’t heard of 99% efficient inverters before. Increasing the number/ size / voltage of FETs will lower R_DS_on, but increase switching losses, so I don’t know if it’s even possible to close the solution. Has anyone here done high efficiency inverters like this before?

  12. you could probibly get better efficiency with an ac drive train. that would of course make some things difficult like pairing it with a battery or regenerative breaking, as you need rectification and inversion stages for those, but direct crank to wheel performance would be improved.

    that said id rather have a crank on an e-bike than no crank. your battery dies in the field you can still ride your bike rather than get out and push. sure you can do direct drive and still recharge through breaking, but if the intended purpose is to use it as an e-bike and only pedal in emergencies, i think having a crank generator is a good idea.

  13. Interesting idea. If generator and motor are 90% efficient, total efficiency is 0.9 * 0.9 = 0.81, or 81%. Added battery or supercapacitor offers interesting possibilities. Especially re free form of vehicle layouts.

    1. That was my calculation. I think at 80 per cent efficiency it might be an idea worth exploring, otherwise it is better to have the traditional transmission or maybe some kind of hibrid.

  14. Interesting idea… until analyzed. Wouldn’t each energy conversion add loss?
    Reminded me of something I read sometime ago: that a lot of animals cheetas, gacelles, dolphins, etc. are more efficient runners than humans, but put the human on a common bycicle and they leave every other animal in the dust, efficiency-wise.
    And don’t get me started on the “digital generator / motor” thing … it’s like calling everything “web 3.0”

  15. This article steps squarely into the middle of a host of biased communities

    Trad Cyclists: ” This isn’t a contest to show off the latest thing you know!! We’ve used chains since the 1800s and that won’t change except for our rechargeable derailleurs, four figure load-cell crank/pedal assemblies and downloading our daily workout to Strava (et al.) to show off to our friends, and I don’t know how cyclists ever got along without matching Spandex.

    Engineers: “Ya gotta be s***ing me. Throw away half the power? Why? Are you heating the frame with it or something?”

    Ebike Fans: “It’s not really an electric moped. Really. No, and neither are the rest. We insist on our right to use them as assault weapons on bike paths and hiking trails because it’s good for old people.”

    Hybrid Vehicle/Industrial HF Drive Sorts: “Well, you could pedal while stopped and store the energy for steep hills, slingshot acceleration and really cool stuff like that. Storage losses and falling over while stopped in traffic? There’s a problem with that?”

    Historians/”Market Forces” sorts: “So you’re saying that a fever-dream design is going to outdo 142 years of natural selection in the marketplace? I’m making the popcorn on this one…”

    I digress.

    1. But I mean that doesn’t mean they are wrong this is honestly just a bad idea like what. This is a vastly worse version of a traditional e-bike. It makes no sense. Especially since the cost of a non-chain bike is already vastly higher, lower efficiency, and only used for very edge cases where a over a long enough time through mud across country where a chain might degrade quickly.

  16. Came here because of the title photo and the “digital drive” catch words…

    I felt a little desapointed by both, so I took my very conventional bike and went for a very efficient spin around.

    The video seems made to attract investors btw.

  17. I am still pretty conflicted about e-bikes. I commute by bike regularly, and am in decent shape (I like to think). It is really disconcerting to have someone blast past me going at least 30mph on the bike path riding the equivalent of an electric motorcycle. I tend to agree that pedaling at such high speeds is really just for show. I like the guy above that said he just took the pedals off.
    At that point you’re basically riding a Vespa anyway but abusing bike paths and arguably creating a hazard. I mean, if you ride a regular bike after a month or so you would be in much better shape.
    On the other hand, I guess getting people out more and out of cars to enjoy nature or something is a benefit.
    Oh also as to regenerative braking- about useless on a bike. At least for me, I use the brakes as absolutely minimal as possible, and often take my whole 10 mile committee not touching the brakes once except at the entrance to the building.

    1. Here at least to count as a bicycle the electric assist has to cut out at a low speed, top of my head I think its 15mph and to be legal it must only ‘help’ while you are pedalling and up to a pretty low power limit, can’t recall exactly what but its only a few hundred watt. Anything over that you have to register it as a motorbike, have the bike license etc…

      Under that sort of restriction – so it really is just flattening the steep hills and letting the less fit folks get where they want to go while hopefully improving their health at the same time I have no problem with e-bikes. Its only when you lack regulation (or enforcement) so your motorbike in every way but name can abuse the system I have anything against them.

      I still personally don’t think I’d want the added weight and complexity of an e-bike unless it is also a cargo bike or something – needs a reason to be heavier or some other benefit from having the the e-bike battery that means you might as well put in the motor – perhaps good lights to help those pesky cars spot you.

  18. Stresses and wear on the thin chain, sprockets, and shift components would be better reduced by a simple hub motor on the front or rear wheel and small battery pack. These are already commercially available. A fully “digital drive” would not withstand steep continuous hill-climbing situations. If you want a “workout machine”, connect a motor or alternator to an exercise bike like everyone else does on social media.

  19. People in this thread are crying over a hypothetical 60% efficiency figure without a single thought as to what it means. Yes, the absolute efficiency of energy from your leg to the ground is lower, but that’s not the problem being solved. If you truly care about efficiency, you’d walk instead of wasting energy on the mechanical losses in your bike. It’s a stupid thing to be up in arms about.

    Every single person who has ever ridden a bike has had to get off and walk it up a hill. There’s no way around it, you just can’t get enough leverage on the pedals to move up the hill and maintain enough speed to stay upright.

    What this does is give you the ability to keep pedaling at a comfortable pace regardless of the terrain. You can just sit there and pedal at whatever speed you can comfortably sustain until you get to your destination. The energy is used less efficiently but you can *make more of it* and do it more comfortably. You can ride through a hilly town with the same effort as riding on a flat road.

    Extracting more energy from the user with less effort is *great* if your goal is exercise. This is also fantastic if you have limited strength or endurance. Old people, or those with disabilities or injuries sometimes are physically not capable of expending the effort it takes to bike up a hill or on uneven terrain. By letting them pedal at a comfortable pace and managing that energy as stored electricity, this enables those people to bike actively and keep up with able-bodied or just stronger riders.

    Grandma doesn’t give a shit if 40% of her pedaling is “wasted” if it means she can bike to the corner shop when she couldn’t before. Your uncle with a bum knee doesn’t care because it means he can bike uphill with his kid again. Beth’s favorite hobby was the bike path by the river until she broke her ankle, now she can ride again without hurting herself.

    Get off your goddamn high horses for three seconds and think about someone less fortunate than yourself.

    1. When going up hill mechanical losses are insignificant and it is strictly a “how many watts can you put down?” Issue. The un-fit cannot go slow enough on a bike for it to not fall over. When walking you can go as slow as you want without falling over down to zero speed. As stated above the mechanical efficiency of a bike is 95% there is very little energy wasted on a bike.
      This bike extracts less energy from the user. It’s worse in every way from an engineers perspective but still has merit as a research platform and like I said above if it gets people out of cars all the better.

    2. Aside from the potential benefits from a lack of a chain (maintenance, physical layout) there is nothing that a direct drive hub motor ebike couldn’t do.

      You can get regen in all the same ways, even at stops with the right kickstand which would be required for any bike to be pedaled at a stop. It’s cheaper and lighter with only one motor as well. Regen gets poo-pooed a lot in general, and while it does add a small efficiency gain to the overall system, it’s main benefit is that you don’t have to replace brake pads anymore, and is safer with two braking systems instead of just one.

      It allows elderly or otherwise impaired individuals more access and ability. There is still full control over the assistance, take-offs and hills can be easy. You can pedal at whatever cadence you like. There are both cadence and torque sensing options depending on how you want it to feel.

      It’s interesting from a design perspective, in an artsy kind of way, but it’s benefits aren’t exclusive to the style, and comes with more comprise than other options.

    1. Fixed wheel forever! If a regular bike is 95% efficient a fixie must be… more! It’s my regular commuter for my almost 10 mile ride which is really flat. Weighs about nothing, steel frame and tolerant of a decade of abuse with nearly zero maintenance . I do have a front brake that just takes up space (no need for braking except near door of the building and even at that a back pedal works well) but is there mostly for occasional urgent use and to ward off “you irresponsible &&&$&!! ” brakeless comments. Seriously fixed gear bicycle is apex of 100 years of practical engineering. It is darn near perfect especially for my use case. PS I love bikes.

  20. hahah i’m surprised to find i’m much more positive than the mean here.

    in the real world, i like a single-speed acoustic bike. i’m not crazy about anything newfangled…i don’t mind other peple with their ebikes but for me i don’t want it. and yet, this idea is pretty exciting to me. yeah, the efficiency figure is a show-stopper…and realistically, that won’t be overcome in my lifetime (though i will probably become more interested in ebikes as i slow down with age). but still, the fact of the matter is, i’m tired of maintaining my drivetrain. chains don’t last long, and now i’m getting more life out of my chain but at the cost of cleaning and oiling it more often. i destroy the chainrings/sprockets and the bearings too. and twice i’ve had crashes from the chain coming off when i was foolishly torquing hard at high RPMs (it was fun until it wasn’t).

    so, obviously, this wouldn’t obviate all of the wear parts, but the idea of having a thin copper wire carrying my power instead of the chain and gears…it’s a little bit attractive. wake me when they solve all the practical problems with it :)

    maybe the hydraulic idea like Gregg Eshelman suggests would be practical sooner. i could definitely imagine just a couple hydraulic lines running, instead of a chain. i don’t know much about different hydraulic mechanisms but i imagine the efficiency could be pretty decent, with relatively simple devices. otoh, maybe maintaining a high pressure piston is even worse than maintaining a chain. i don’t know.

    1. High pressure usually means heavier components. Hydraulic transmission is used where weight is not really a consideration, ie. for heavy machinery, rail locomotives etc. If you want a 50 Kg bicycle, that’s the way to go.

  21. Wow, this is not what we need: a far less efficient bike.
    Just to avoid someone patenting even worse ideas, I write it down here: wireless power transfer! Let’s use inductive and or magnetic and or electromagnetic means to transfer the power. Even more ‘design freedom’ at the cost of the planet.

    1. What’s the efficiency of a work of art? If all we wanted was efficiency then let’s all eat tge6same tasteless optimal gloop for every meal.

      Here is an idea for a drive train: The cyclist powers a water pump which pumps water upwards, which then falls onto a water turbine powering the rear wheel. Efficiency? Perhaps 70 x 95%, which is still ore than 58%. The water is completely recyclable.

    1. i can’t think of how to make the geometry work out. the modern “safety bicycle” is a real sweet spot.

      if you are balanced over the front wheel, the thing wants to throw you over the handlebars (like a pennyfarthing), and if you’re balanced over the rear wheel then it wants to fall backwards. you want to be between them. if you’re recumbent, you can be balanced in the middle while having the pedals in front of you, but then you’re pedalling on the steering wheel. i guess a recumbent with tail steering could do it???

      of course, getting rid of the tiny losses from chain is only relevant if you’re working on performance but generally recumbent doesn’t get your best performance from your engine (the meat sack payload).

  22. I think there must be a battery which runs the electric motor and pedal or generator should be used to replenish the battery. If the electric motor of front wheel works as generator too it can also replenish the battery.

  23. Watch the video – the speaker basically advise that one of these bikes is around 50% efficient, and a traditional chain driven mike is around 95% efficient.

    The speaker points out that if this is an issue, you can always add more batteries.

    So basically these bikes are a second-rate e-bike with the addition of a pedal powered generator.

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