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The idea of a digital drivetrain is simple.  You have a power generator at your crankset,   which converts your pedal power into  electricity. You've then got a motor   at your drive wheel. Two wires transmit  the power you're generating straight to   the motor, and a few electrical  components sort out the details. As sci-fi as this looks and sounds, it's not at  all a new concept. The first patent for a digital   drive bike was issued as far back as 1975, and  the first fully functioning digital drivetrain   was shown in 1995. The first production bike  with a digital drive was released in 2012,   and currently, we're seeing a handful of companies  working on their own digital drive systems. Current bicycles often use derailleur gears  and chains. These drivetrains have improved   incrementally over more than a century and  have well and truly proven themselves to   be lightweight, high-performing,  efficient, and cheap to produce. More recently, gearbox drivetrains have  come a very long way. While they'll never   be as light or efficient as a derailleur  drivetrain, they are incredibly reliable,   and very low maintenance. Plus, when  you pair them with a belt drive the   component longevity is increased, and  the maintenance is reduced even further. But are these drivetrains the  pinnacle of what's possible? Or   will bicycle drivetrains of the future be digital? In this video, we're going to explore the  world of chainless digital drive bicycles. There are many advantages  to digital drive. Firstly,   you lose the chain. This means no wear and  tear on the drivetrain, no greasy fingers,   lower running costs, and less bike maintenance.  A bike with digital drive would essentially   just need its brake pads and tires replaced.  This would be ideal for those using a bike   in all weather conditions, and it would  be great for fleets and hire bikes too. Secondly, you end up with a fully automatic  bike with an infinite gear range. This is   particularly advantageous for inexperienced  cyclists as the digital drive would always   have you in the perfect gear. Top-tier  gearbox drivetrains with automatic gear   shifting are currently both complex and  very expensive. A digital drive equivalent   has much less complexity and could feasibly be  significantly cheaper with the same features. You could also add a battery, or supercapacitor,  that you charge while you ride. By choosing to   send some of your pedal power to a battery,  you could use it later - for example, when   taking off from the traffic lights, or to get over  small hills. And if you were using a three-wheel   cargo bike, you could even charge this battery  while you're waiting at the traffic lights. In addition, you could capture energy at the motor  while descending or slowing to a stop - this is   known as regenerative braking. The motor could  integrate an electrical anti-lock braking system,   and when you've parked your bike, the  motor could be mechanically locked. A digital drivetrain could perfectly optimize  your pedaling technique. The system would always   have you riding at your optimal power  output and cadence, which would result   in the highest possible efficiency of your  body. You could also do interesting things   with the pedaling characteristics, such as  electronically eliminating dead spots in the   crank revolution. What I mean by this is that  the generator resistance could be increased   when you have the most crank leverage, and  reduced when you have the least leverage. Another example where a change in  pedaling characteristics could be   useful is if you're rehabilitating from an injury,   or have a disability. Let's say it's  your left leg. You could program a   digital drive to have less resistance on  your left leg, and more on your right. Digital drive also opens up new  bike design options. For example,   you could have interesting folding bike  designs, different cargo bike layouts,   and multiple people pedaling the same  bike at their own perfect efficiency. Alright, the advantages are sounding pretty sweet,  but there are, of course, disadvantages too. The big one is drive efficiency. Converting  between mechanical energy and electrical energy,   and then back to mechanical energy - is very  inefficient. When you put power into your pedals,   a single-speed chain or belt drive will put  more than 95% into propelling you forwards.   In comparison, a digital drivetrain will likely  lose around 20% of the power at the generator,   and another 20% at the motor. With  some step-up and step-down gearing   to get the power ranges right, you  might lose another 10%. In total,   we're looking at close to half the  efficiency of a chain drivetrain. To put this in perspective, a chain drivetrain  would have you riding 27 kilometers per hour on   the flat at 150 watts, while a digital drivetrain  would have you riding a full 17% slower. And on   a slope, it gets even worse. A five percent  gradient with a chain would have you cycling   at 9.4 kilometers per hour, and you'll be  cycling 34% slower with a digital drive. But keep in mind these numbers don't account for  any energy captured through regenerative braking. Digital drive would also add at least 25%  more weight to a bike. The lightest rear   hub motor is more than one kilogram heavier  than a regular hub. Plus, you can add at   least another kilogram for the front generator  and wiring. And given there is no mechanical   coupling between the pedals and rear wheel,  a digital drive motor needs to be especially   powerful to make up for it. An appropriately  powerful motor could be 2.5 to 3 kilograms.   All rear hub motors cannot take advantage  of your bike's gears to operate in their   optimal RPM range for both steep uphills  and flat riding. Unless you use very large   and heavy motors, digital drive can only  really be geared for one or the other. Combining this with the high motor weight,   it's also less ideal for a  mountain bike application too. Digital Drive also relies very heavily on  software and the controller. If the motor cannot   be controlled within a couple of milliseconds, it  will not have the same feel as a chain drivetrain. Okay, so the advantages are big,   but the disadvantages have really stacked  up too. So let's break things down further. I've discussed the pros and cons when comparing  digital drive fitted to a regular bike. But things   get way more fascinating when we talk about  the possibilities of digital drive e-bikes! When a digital drive bike is used in conjunction  with a battery it's sometimes known as a "series   hybrid pedelec". Digital drive bikes already  have all of the components of an e-bike,   so fitting up a battery to not  only provide some power assist   but also offset the extra weight and  transmission losses just makes sense. The only production bike you can currently  buy with a digital drivetrain is the Mando   Footloose. This bike is at least  a decade ahead of any other bike,   so the drivetrain is not a particularly refined  product. From all reports, it feels like you're   walking up a stair climber rather than pedaling  a bike. And the lag between the pedals and wheel   torque results in a lot of surging. Part of the  issue here is the software. If the controller   uses basic algorithms and cannot control the  motor quickly enough, or provide appropriate   feedback to the rider through the generator  - the digital drive will not feel natural. One reason why the Mando Footloose is the  only digital drive bike available is that   the German approval body for e-bikes has  until very recently classified digital   drive bikes in the same category as motorbikes  and mopeds, rather than as a bicycle. German   bicycle shops attempting to sell the Mando  Footloose even risked a 5,000 Euro fine. A more advanced digital drive system that  never made it into production was found on   the EE-SpeedBike. Using advanced software  simulation of a chain drive in combination   with special control algorithms to  manipulate the components, it has   been described as riding just like a regular  bike. The EE-SpeedBike weighs 29 kilograms,   can travel at 45 kilometers per hour, and get  80 kilometers of range with medium assistance.   It'll be interesting to see where this technology  heads next - it looks like Schaeffler might be   using some of the patented control electronics  from this bike in their new Free Drive system. Okay, we need to talk about efficiency  again because it's often viewed as a   real sticking point for digital  drivetrains - but it need not be. Firstly, drive efficiency is a lower priority  for some cycling applications. Commuter bikes,   bike rental fleets, and especially cargo bikes,  are examples where the possible extra weight   and reduced range are far less important. And  in any case, you can easily a bigger   battery to achieve the required range. But the  difference in drive efficiency to a chain drive   bike might not be as large as we previously  discussed. Given the right circumstances,   and provided you have smart ways to save and use  power. When the motor is doing the majority of the   work, digital Drive e-bikes are closest in drive  efficiency to chain drive e-bikes. For example,   if we compare a mid-drive e-bike to a digital  drive e-bike with 200 watts coming in from   the battery, when we cycle at 50 watts power  output, we can theoretically achieve similar   drive efficiencies. This is because there is only  a small amount of energy lost to the generator. I found a great thesis by Edgar Tournon,  a student at Claude Bernard University who   explained that with his digital drive system,  effective drive efficiency of close to 75% is   possible on a five-kilometer flat course, and it's  62% if you add a 50-meter hill in the middle. The   reason the efficiency is so high is that energy  can be recovered by the motor when slowing for   traffic lights or cycling downhill. This is  something that I didn't factor into my earlier   efficiency estimate. In stop-start situations,  digital drive bikes can be quite efficient. Edgar also determined that his drive  system would even keep up with regular   chain drive bikes on a stop-start city  commute, provided his digital drivetrain   had an efficiency of around 70% and  he could use regenerative braking. But perhaps it's not the bike that needs the  efficiency optimization, but rather the human. Another promising aspect of digital drive is  that the system can make you - the rider - more   efficient. Our bodies work most efficiently  at a nearly constant load rather than a highly   variable one. To maintain a constant load we  need to always select the right gear ratio and   cadence for different riding situations. We don't  always get this right, but a digital drive could,   offering the most efficient extraction of  power with the lowest levels of body fatigue. Okay, I've got a few more interesting takes  on digital drive and its possibilities. Electric motors have very fine control over how  much torque output they offer, which gives us the   opportunity to intentionally limit torque and  mimic what it feels like to have gears. There   is absolutely no reason to have '' digital  gears, but hey, it could be fun, and I like fun. You could use a digital drive bike as a  workout machine by programming it to offer   outdoor interval training without a change in  cycling speed. In fact, there are already very   expensive cycling products that intentionally  slow you down so you can train effectively. Alternatively, you could put your digital drive  bike onto a stand and train indoors while charging   up a battery, and if the digital drive identifies  that you have strength imbalances between your   legs, it could even apply more resistance  to the leg that needs additional training. Another interesting idea is that digital drive  bikes can easily be coupled with solar power.   With a handful of panels, perhaps you won't  even have to plug in your bike in the future! It was not long ago that professional  photographers were certain that they would   never switch to digital cameras. But through  incremental changes in technology over time,   digital cameras are now the choice of  professional photographers around the world. So, will digital drive follow a similar path? When  compared to a chain on a bike without a battery,   I think it's unlikely. The low  drive efficiency, extra weight,   and inability to efficiently work on flat  and hilly terrain make it an uphill battle. But when it comes to bikes with a battery, I'm  certain that digital drive will be incredibly   useful in the coming years. With the fully  automatic mode that perfectly optimizes your   pedal efficiency at all times, this is going  to be advantageous for anyone who swings a leg   over a bike. Digital drive will be ideal in poor  weather conditions given the lack of wear reduced   bike maintenance, and lower running costs. The  system will also be cheaper to manufacture. The best applications currently are  for cargo bikes, personal transport,   and hire bikes. Expect to see digital drive  on these bikes in the next year or so. I'm also really looking forward to the new  bike designs that will come about as a result. So, what do you think? Will digital  drive bikes be big in the future?