The Copenhagen Wheel

Commuter, Concept, Student Design 12 44

“Transform your ordinary bicycle into a hybrid e-bike that also provides feedback on pollution, traffic congestion and road conditions in real time!”

That is the opening statement on the website for the Copenhagen Wheel, a project by MIT’s SENSEable City Laboratory. With a claim like that, it is no wonder the project has been getting so much attention on the web since its debut at the COP15 climate Summit in Copenhagen a couple of days ago. Like the Sanyo Eneloop bike that I mentioned last year, this design stores kinetic energy from braking for future use by way of technology similar to the Kinetic Energy Recovery System (KERS), which has changed Formula One racing dramatically in recent years. Unlike the Sanyo bike though, this design stores that energy in a battery that is contained in the wheel, not on the frame of the bicycle. For that reason the Copenhagen Wheel is retrofitable on any type of bike (including the Cinelli Mystic pictured here courtesy of the SENSEable City Lab’s website).

In addition to a battery and motor, the Copenhagen Wheel has a variety of other functions that are hidden within the oversized red hub. By using a series of sensors and a Bluetooth connection to the user’s iPhone, the wheel can monitor the bicycle’s speed, direction and distance traveled, as well as collect data on air pollution and even the proximity of the rider’s friends.

“One of the applications that we have discussed with the City of Copenhagen is that of an incentive scheme whereby citizens collect Green Miles – something similar to frequent flyer miles, but good for the environment,” says Christine Outram, who led the team of researchers at MIT.

You can read more about the technology, and the team’s ideas behind the design, at the MIT Media Relations site.

The idea of storing braking or downhill coasting energy, and using that energy for a burst of speed later is nothing new. Whitt and Wilson’s 1982 book, Bicycling Science (coincidentally…or not… published by The MIT Press), discusses energy storage systems going back many years. Thirty plus years ago, the most successful designs used flywheels to store energy (as opposed to those systems which relied on elastic bands or springs). Flywheels are heavy though, so the practical application for bicycles was pretty limited. Even with modern technology, some would argue that practical applications of energy storage systems are still debatable. In a New York Times article about the Copenhagen Wheel, Dr. William Mitchell, who runs another lab at M.I.T. called SmartCities, is quoted as saying:

“Regenerative braking hardware adds mass, complexity and cost, and the energy efficiency gains from it turn out to be surprisingly limited.”

Steve Hed and Jens Martin Skibsted are also quoted in that NY Times article, so be sure to read it for a different perspective than you get from the MIT press releases. Another place to read about the Copenhagen Wheel is TreeHugger. They mentioned it in a post along with 4 other bike solutions spotted at COP-15.

Not related to the wheel, but while I am throwing out Copenhagen related links, I’ll mention this StreetFilms video which features Mikael Colville-Anderson from Copenhaganize talking about bicycle infrastructure projects in that city. Great stuff! Watching that video akes me want to visit Copenhagen all the more.

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12 Comments

  1. Pete Hindle December 17, 2009 at 4:05 am -  Reply

    This project is getting a lot of flack for being a totally unrealistic idea. Anybody with any intelligence knows that the idea of creating custom new expensive technological objects to do this job goes against everything that needs to be done at the Copenhagen summit; the fact that this is offered as some sort of "solution" is a sorry statement about the uphill struggle we face.

  2. Daner December 17, 2009 at 11:07 am -  Reply

    Using regenerative braking to recharge the batteries is a good idea, but putting all of the extra weight into the wheel itself is a big mistake. If the object is to make it easy to retrofit to standard bikes, come up with a chargeable Li-ion pack that can be mounted on bottle cage mounts or a rack. Keep any extra weight low, centered (and if applicable, sprung) and you will do much to retain the handling and responsiveness of any bike. Place extra weight too high, too far away from the center or add unnecessarily to the rotational inertia of the wheels and you create handling problems that need not exist.

  3. Ron December 17, 2009 at 12:36 pm -  Reply

    The pertinent questions I ask would MIT is the energy content of battery (Wh/kg) and energy use per distance (Wh/km). 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 the true cost of riding the bike or a bike equipped with the wheel.

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

    I'll give a perspective. A 180 lb man with a 20 lb bike traveling at 15 mph needs 2026 joules or 0.56 Wh of K.E to come to a stop. With what efficiency will the recovery system be able to capture some of that? 70%? 80%? Let's assume 75%. 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.

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

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

    So realistically, 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 large amount, it may make sense of a crowded urban area, otherwise not really considering buying costs and lifecycle costs. Also considering Copenhagen is on the route to "biking highways" in future (2012+), I expect some of the stopping needed to go away so then the question is, will a technology like this even be necessary then? Perhaps NYC can really make use of this. You can provide such a technology to those poor pedal cabbies and save some of their energy. I see a lot of practicality in something like that.

  4. Andrew December 17, 2009 at 3:57 pm -  Reply

    Realistically, there are plenty of "eBike in a Box" kits out there comprising a battery pack and a rear motor-hub laced to a wheel. Many of them are made in China, and undoubtedly dramatically cheaper than this one.

    Regenerative braking is probably not a practical solution on vehicles as light and efficient as a bicycle, especially in the rear-hub, since only a small proportion of braking pressure is exerted on the rear of a bike.

    Ebikes make sense for a lot of people who just want to get where they need to go with a minimum of fuss, so I have no problem with the concept, just the execution (Daner does a good job of outlining the problems with this one).

    As far as Pete's comment, your argument really goes beyond the scope of this blog, or of bicycling, period. The fact of the matter is, the amount of influence that an individual person has on the global issue of climate change is pretty trivial. Obviously, the solutions need to be macro-industrial, political, and social ones. Personal 'greening' is pretty much just to satisfy our own egos and make us feel like we are actually significant in some way (and I say this as a car-less vegetarian for sustainability reasons, so I'm being a bit cynical beyond my hypocrisy).

  5. Anonymous December 17, 2009 at 4:27 pm -  Reply

    For a 1500 kg car moving at high speed, regenerative braking makes sense. I don't see it being practical in a mode of transport as light as the bicycle. Or perhaps it will be, as Ron said, with a lot of stops on the commute. So if you're not stopping as much, you're not going to take advantage of regenerative braking so its conserving energy only at certain times. Going with an e-bike also takes care of the apparent compatibility problems you'll have putting a wheel with a hub on separate bikes and separate designs. Thats my take…

  6. Pete Hindle December 17, 2009 at 4:31 pm -  Reply

    Thanks Andrew – I'm really enjoying this thread, and Ron's breakdown of the physics was very interesting. I realise I came off like a hair-shirt vegan in the first comment… my bad!

  7. James December 17, 2009 at 8:41 pm -  Reply

    Great comments so far! This is just the type of discussion I was hoping this post would generate.

    Ron and Anon 4:27 make a great point about the practicality of regenerative braking for a car vs. a bike. What may make sense for a car, especially an F1 car stopping rapidly from 200mph, does not necessarily apply to a slow moving vehicle with a total weight around 200 lbs.

    The weight distribution point made by Daner and others is a very good one too.

    Still, I am glad to see more engineering resources these days going toward all types of e-bike development. Time will tell if this develops into anything, but for now it is a great catalyst for more discussion. Keep the comments coming!

  8. B. Nicholson December 18, 2009 at 3:42 am -  Reply

    Wireless is nice and solves a lot of terrible problems, mainly with reliability. The geared up inside, also wireless, is a step up in reliability and utility, making the Copenhagen Wheel the best hub motor I've ever seen. The efficiency gained with the gearing, though is lost with the battery in the wheel. The battery can be wired through the hub into fenders or 'hub caps' anywhere so they won't have to be dragged around the hub and you have a much more efficient, much more reliable, much lighter set up than anything on the market now. Yeah, dump the regen, unless you yodel.

  9. Anonymous December 18, 2009 at 12:59 pm -  Reply

    Neat wheel (though it should go on the front which actually does most of the braking), but why the hell does it have to be a fscking iPhone?

  10. Anonymous December 19, 2009 at 6:50 am -  Reply

    Forget Copenhagen. You should visit Amsterdam to see a city of bikes.

  11. Benjamin December 22, 2009 at 10:20 am -  Reply

    I think the interest and recent hype about this concept is certainly constructive on many levels…The negatives about whether it can really work or not, and how much energy is needed for the concept to be a reality is valid…However, I would certainly rather to focus more myself on the value behind the concept and how it becomes a response to the need for ideas revolving around sustainable transport. That it in itself is more important than whether it can work or not. I think this concept has gained intrigue because it's really aiming to solve something..It may not be the first and it won't certainly be the last but this is a good start. Not to mention, if MIT is involved, something good should happen.

  12. Erik Orgell December 22, 2009 at 2:39 pm -  Reply

    Unless it can be plugged in and used as a pre-charged power source I am not seeing much utility in adding so much weight, expense and complexity to a bike to sole recapture a fraction of energy lost in braking.

    I am all for innovation and new ideas but I'm not really seeing this as being a great solution. It might be usable and a step in the right direction but it isn't there yet.

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