Tuesday, January 19, 2010

20 Practicalities Concerning The Copenhagen Wheel

Good morning!

For lack of a super-stimulating post today, I thought I'd immerse myself a bit in the hype surrounding the Copenhagen Wheel before the subject becomes rusty and unwrap this pretty looking present.

So I'm taking it for granted that you folks will have some prior knowledge of this new hybrid e-bike introduced by MIT's Senseable City Lab.

Well, the folks are not actually marketing a bike technically.

They actually demoed a hub-motored wheel during the Climate Summit in December that you can shift around and adapt to different bikes for "city riding", the idea being that it stores energy through regenerative rear wheel braking action and gives it back to the rider when they need a 'boost'. It is sort of a leaner, maybe meaner version of the gas powered Revopower idea that never took shape. Remember that?

An attractive proposition is that this wheel can be monitored by a smart phone via blue tooth and all the electro-mechanical aspects are packaged into one assembly - the wheel itself. And then it measures environmental variables like noise, pollution and so on and throws all that data into your phone for your city riding pleasure.

It is by all means an academic project, funded by the city of Copenhagen, Ducati Energia and the Italian Ministry for the Environment.

Now when I hear of projects like these, I switch off the ads and start looking into specifics. I thought for an institution like MIT, you would expect to see some numbers posted on their website at the least, or a whitepaper indicating weight, wattage requirements, cost, efficiency etc. I certainly haven't found much other than a Java based applet you can sort of play around with.

So here are my questions & concerns for the boys and girls at MIT, which I think I sounded off a month back to Bicycle Design.

What is the energy content of the battery (Wh/kg) and energy use per distance (Wh/km) of this product? Multiplying both will give us an estimate of distance/kg of battery weight and total energy capacity per charge. Knowing cost of electricity, someone can easily calculate the true cost of riding the bike or a bike equipped with the wheel and then compare it with with a bike not equipped with it.

Then comes the question of braking energy recovery. How many stops would a cyclist have to make to recover at least 10% of the total battery capacity back and by how much will their range be extended?

Let me give you a perspective. A 180 lb man with a 20 lb bike traveling at 15 mph has 2026 joules or 0.56 Wh of kinetic energy to shed, in order to come to a stop. Note : These are back of the envelope calculations I just roughly did.

So, with what efficiency will the recovery system be able to capture some of that? 70%? 80%? Let's assume 75% which is a reasonable number. With that, I can get back 0.42 Wh or 1516 joules back, but I can only put this energy back into the battery at a certain charge rate which really depends on the battery's specs.

So for illustration, if battery's max charge rate is 100 joules/sec, 1516 joules will take 15 seconds or more to put back in.

Now realistically, no one takes that long to stop, even though the US CPSC recommends that brakes should stop a cyclist in 15 seconds from 15 to 0 mph.

So realistically, let's say people take about 3-4 seconds every time to stop. Using the 100 J/s charge rate, cyclist can only put in 400 Joules or 0.11 Wh back every stop. So the question again becomes, how many times does a cyclist have to stop to put back 10% of kinetic energy of braking, at 75% efficiency to get the extra amount of miles, given the limitations of the battery?

If its a reasonably good amount, it may make some sense in a crowded urban area like Copenhagen, otherwise not really considering buying costs and life cycle costs. Again, only the average numbers over long riding in the city will give you any solid perspective on the practicality.

In short, without specifics like what I'm calling for, no one should start rooting for this product as a game changer just yet, for that is just silly in my book - a case of inflated yet unwarranted attention that a lot of blog fodder command these days.

Sometime back, I noted that the city of Copenhagen is en route (forgive the pun) to "biking superhighways". With that kind of a future for this city, I expect some of the stopping usually encountered in tight city riding conditions to reduce. So then the question is, will the Copenhagen Wheel even be deemed necessary then?

As usual, I ask too many bothersome but nevertheless important questions. The answers are reluctant to arrive. Or it just might. Right MIT? :)


  1. Paul Rockwell10:36 AM


    Great post. Don't you think it's odd they would apply all this tech into a rear wheel? As we all know during braking, weight shifts from the rear to the front. Makes more sense for the front I believe. And the kinetic energy recovery proposition for a light weight bicycle has been tried and tried over the years, never really got anywhere. You can't do but wonder whether MIT did an exhaustive research of what was tried years back, before jumping into the work they've done here.

  2. Paul : Yes and no. Yes because of what you mentioned and how COG maybe shifted more to the rear. No because all that instrumentation would be safer in a front impact during an accident. Just saying.

    Well I just emailed MIT these thoughts so I'm hoping for a good discussion from who are actually involved with it.

  3. Anonymous10:52 AM

    If you travel short distances every day and install solar panels into your car roof you can travel forever without buying fuel. Why don't people invest more in that idea instead of fiddling with regenerative braking?

  4. Anon : I wouldn't go as far as to say people are not thinking solar for bicycles (I hope you meant applying it to bikes, not cars).

    Bicycle Design ran a design competition last year on its blog and the winner chosen by a jury of prestigious designers was a bike with a solar panel on its roof, sort of like a two wheel rickshaw. While the idea sounds good on paper, its a challenge design wise and cost wise to incorporate the panel and all the electronics into the kind of form the winner suggested. It involves more thought, definitely just like the Copenhagen Wheel.

  5. You have some good questions not many bothered asking. Certainly you have to come to Cozy Beehive to get your daily dose of reality.

  6. Anonymous8:10 PM

    Thanks for the article, too much nonsense gets passed along without anyone applying reality checks or basic analysis.

    As long as the rear wheel is on the ground, the weight shift won't matter. Also a heavier rear wheel will affect the handling less than a front wheel at least for most conditions a commuter bike will see.

    Portable solar is difficult. I've used some portable solar to keep camera batteries charged and I found it was difficult. Wrong angle, and shade from trees and structures or clouds are constant challenges. It can be hard to find a spot that will work even for a couple of hours. And if you're moving even more difficult. You'd have to park in a place that was going to have sun for many hours to even consider this practical. Sounds easy until you try it. I suspect that connecting to the grid is more cost and environmentally effective. Don't forget you have to make and carry around solar panels that aren't doing anything most of the time.

  7. I guess I can see the market for something like this but I'd never want one on any bike of mine. I'm pretty sure the negative aspects of having an extra 15 lbs of weight in a wheel far outweigh any gains for me.

    I was getting REALLY tired of this thing showing up everywhere for a while.

  8. Anon : Absolutely agree. The angle of the solar roof on a bicycle is static and has to change if you want to take full potential of the solar aspect. Otherwise its a waste. And you do have a point about the handling if the Copenhagen Wheel would be on the front. Good points.

    Clinton : Exactly, that's the issue here. If there are 200 people like you somewhere in Copenhagen you said the same thing seeing the item, is it a success at its promise of luring the customer? If you want to talk about "smart cycling", I think that we're not too far away from a device that can monitor environmental variables of riding that is as svelte and compact as a IbikePro, that can be handlebar mounted. No need of placing that all on a heavy rear wheel.

  9. Personally, I think the whole Copenhagen wheel is a gimmick and a continuation of the overcomplication of the simple art of urban cycling.

    Interesting to read your tech angle on the wheel, but I can't see how it will be very popular. It's expensive, subject to theft and bothersome.

    Electric bikes are on the market here in Denmark, marketed at the elderly mostly, but I don't see them being sold in any great numbers in countries that have established bicycle culture. Maybe for some people who have a longer commute.

    word verification: Messin. They're just messin' with urban cycling...

  10. Thanks Mikael, you obviously got my twitter shoutout. Anyway, interesting comment you have there, that coming from the blogger of Copenhagenize must mean something. Looks like you don't buy into the idea of electric biking, leave alone hybrid biking. But I do think the demand of electric bikes is real, except that it is very unbalanced. One statistic I read somewhere quoted a number of around 23 million electric bikes sold around the world in 2008 and more than 90% these are made and sold in China. The rest of the world seems to be perfectly alright with
    conventional bicycling, I suppose.

    So you think MIT is on a purposeless mission to interfere with urban cycling in Copenhagen, is it?

  11. just my opinion, but I think this is a way for MIT to capture few research grants and attract more attention to their institution. what better time to do this than targeting the climate summit? that's a big stage MIT got there. perhaps they're not really worried in how practical the design will actually turn out to be. or maybe this is just my opinion, and as we all know the first few months before a odd design comes out, there is widespread criticism everywhere. but then certain designs do make it to see light of day and also manage to turn around public opinion. like the shimano di2 system.

  12. putting regenerative braking on a bike could make sense, especially due to the small amount of energy return needed to realize improvement.

    It does strike me as odd that the unit is in the rear hub. Braking often reduces speed in a much shorter time than similar increases in speed. Bicycles, like motorcycles, when properly operated, utilize the front wheel for much more braking than the rear wheel.

    If the regenerative braking system is in the back hub, it is either somewhat dangerous due to long distances for emergency braking, or inefficient due to being assisted by a non-regenerative brake on the front wheel.

    I rarely see a tire spinning due to pedalling too forcefully. I have often seen bike rear wheels slip due to excess braking. I would prefer a regen system provide powerful rapid braking with return of that energy over a longer period than slow braking and wheelie stands.

  13. About the best that can be hoped for is a 10% range increase from implementing regenerative braking. There are many home-built electric motorcycles on which regen has been implemented and some of the production electric motor scooters from China also implement regen (in both cases through the rear drive wheel).

    Typically, electric bicycles are very low power as compared to electric motorcycles, and, as a result, accelerate slowly. Typically, deceleration via regen braking is limited to about half of the maximum acceleration rate, because the battery recharge rate is often limited to about half the discharge rate. This means the regen braking in an electric bicycle is very modest.

  14. If I wanted a bike that captured "information about your personal riding habits how much effort you are putting in, calories you are burning etc as well as information about your surroundings, including carbon monoxide, NOx, noise, ambient temperature and relative humidity"... then perhaps I would also want a regen system to add weight to my bike. If I wanted to tweet such info to one of my friends, or if I wanted to have my bike's function controlled by a cell phone... then perhaps I would want the Copenhagen Wheel. But what I want from my bike is light weight and simplicity, rather than gee-gaws and gizmos.

    Your comparison to F1 cars is apropos. The F1 system provides 82 hp for 6.6 seconds per lap. That, in comparison to the hundreds of hp used for a minute or two per lap, is a very small amount of energy. If the bicycle system stores significant amounts of energy (enough to help you pedal up a hill) it will also have significant mass. I can't imagine that the unit is much less than 10 lbs, about the difference between a very light sophisticated bike and a cheap, very heavy one. Thus, the Copenhagen wheel effectively converts your $2,000 bike into a $150 bike.

    Regen makes sense to extend the range of an electric vehicle (and to reduce wear on brakes) particularly when implementing it is virtually free. But making a bicycle harder to pedal all the time for a limited boost up an occasional hill makes little sense to me: The braking energy recovered is a very small portion of the energy needed to make it easy to pedal up a big hill.

    Under certain contrived conditions (such as a bicyclist trying to maintain a constant speed while going both downhill and up, by braking on the downhills) the device could be vaguely useful. However, bicyclists are rarely forced to maintain constant speed. The most efficient way to traverse hills and valleys to to act like a pendulum: the last thing I want at the bottom of hill is low speed going in.

    Around town, I mainly coast to a stop, with a little jab at the brakes at the very end. This would give me very little stored energy.

    I'd have to see a lot of actual test results to be convinced that a Copenhagen Wheel-equipped bike is anything but less efficient than an ordinary bike.

  15. They might dump the energy into a capacitor, then trickle it from there into the battery.

    Energy stored in a capacitor = 1/2 C V², where C is the capacitance (farads) and V is the voltage. So for example if you had a 1 farad capacitor, storing 2 kJ would require around 65 V.

    A quick Google search turned up this discussion.

  16. Anonymous11:02 PM

    This is 21st century alchemy...
    turning BS into Gold.

    Missioncycles is right, this is no more than an exercise in extracting gov't $$$ like so many economically inviable "green" projects..ie. solar, wind, continued global warming research (why if the science is settled...right).

    Think about this as a cyclist (unlike the inventors). You add 10+ lbs for an tiny ephemeral "boost"(?) but if the hill takes longer than 10 seconds to climb...won't your total energy expenditure be GREATER?

    Forgive my cynicism..but this project could exist only if all rules of physics & economics are repealed (ignored)....just like most gov't projects.

  17. DJ : Why capacitor. Why not go supercapacitors? Same thing used in cameras. Those things can power a bus if needed I believe.

  18. Anonymous3:41 PM

    Sorry to weigh in so late, but belated congratulations in any event.

    By tearing into the MIT wheel (I think it's incredibly presumptuous to call it the Copenhagen, referring both to a place where the bicycle system basically works, and the late the ill-starred climate conference/fantasy charade) you've metaphorically opened up the soft underbelly of the entire e-bike industry for all to see.

    Fact is, when you look into any regenerative braking system for something as lo-speed and lightweight as a bicycle, the benefits are modest at best. And as Clinton correctly points out, there'd have to be a lot more benefit here to offset the penalty of an extra 15 pounds on the rear wheel. Basically, it's just an exceptionally crappy flywheel, guys.

    But has anyone done this kind of work on just storing the energy in an actual flywheel and releasing it mechanically? Of course not. Because it doesn't have a hyphenated faux-green e in front of it. (Note: I don't know whether mechanical flywheels for bikes are a good idea or not. That's because I'm a marketing guy with a little bit of technical training, not an engineer.)

    There's a secondary punchline to this joke, too, which is the howling from designers--- not just of e-bikes, but of all kinds of plainly dumb "futuristic" designs that are getting the gee-whiz treatment from nonendemic press this season-- that the bike industry is ignoring (usually via either "narrow-minded thinking" or "internal conspiracy") their wonderful fantasy products in favor of proven designs that actually work.

    Thanks again for shining the light of reason on this particular fantasy. The bike business has plenty of real problems in need of solutions without adding this half-baked PR stunt to the mix.

  19. Rick (@rvmsblog) : Thanks for the comment.

    Isn't it interesting that in bicycle design, there's apparently two emerging factions, one the conservative companies that introduce stuff once in a while with minimal improvements but well tested and mrooted in reality (well, that could be moot but...), the other are the independent designers/firms operating out of various places in the globe who look at bicycle design and go, "hmm, can I do something absolutely mindblowing there to put a good spot into my design portfolio?

    The bike industry has to be narrow minded and perhaps its a good thing as long as they keep products safe. They have to be narrow minded perhaps because there's a regulatory commission overlooking the design of most competition level bikes, the UCI, just like F1 cars are overlooked by F1 committee.

    But I think that mindset of conservatism has perhaps trickled down to other products in their lineup that are not necessarily used for competition. Whether that's a good thing or not is, like I said, moot. I remember in the past, I explored on my blog what perhaps could be a genuine safety device that could be implemented on lowend MTB's, the
    Bud Brake Modulator,from someone in California.

    I wished to do Bud some good by testing this out myself and giving him some modest press, if not hype (as you know I don't review very many products here). After that, he kept emailing me persistently over the course of 3-4 months on how he could effectively sell his idea to the big honchos in the bike industry, because the truth was that NO ONE was entertaining his product! It almost felt like the bike industry cared more about beauty, lightweight-ness and svelte looks over mulling something that may do something more for safety.

  20. Slightly more on topic : Prof. Carlo Ratti on MIT's Senseable Lab contacted me today by email. Hopefully we can get them to chime in and give us some numbers?


    Hi ron,

    These are very good questions - thanks for asking them. I am currently on the road during IAP and so is most of the team (cced). but i think that christine (cced) will be able to get back over the next few weeks.



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