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BMW Megacity – Click above for high-res image

British car mag Autocar has more technical details on the construction of the 2013 BMW Megacity electric vehicle. As we learned last month, the Megacity reverts back to a body-on-frame construction technique that most automakers have abandoned for everything but larger trucks. This, however, is no ordinary body-on-frame. The "frame" is comprised of aluminum extrusions that can be extended or spread apart to accommodate vehicles of different sizes. This is a similar construction technique to the one developed by Lotus for the Elise (and, of course, the Tesla Roadster).

This "skateboard" architecture is also not entirely novel and was used by General Motors back in 2002 for its AUTOnomy fuel cell concept. Tesla evidently has similar plans for the platform of the Model S.

While other automakers describe using different "top hats" (body styles) on their unibody platforms, the Megacity has a more literal interpretation of this architecture. The carbon-fiber passenger cell sits on top of the skateboard aluminum chassis. The tremendous strength of the carbon shell will allow BMW to produce a design with completely open sides and no B-pillars. The rear-hinged back doors will be similar to those on the Mini Clubman.

Like the chassis, the carbon structure can also be extended. The carbon fiber will likely be covered with some sort of skin, possibly a thin layer of aluminum that gives a better surface finish. While the carbon structure saves a lot of weight, it is a difficult material to repair if damaged. Therefore, BMW will make the structure out of smaller sections that can be replaced if necessary. Following the launch of the battery-electric version, a range-extended model with a smaller battery and a 1.0-liter two-cylinder engine could be added to the lineup.



[Source: Autocar]


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  • 16 Comments
      • 4 Years Ago
      I can't understand why more attention is not paid to basalt fibre:
      'Basalt fiber is still not widely used, it is slowly making its way into the hand of consumers. At price points that vary between S-glass ($5/lb to $7/lb) and E-glass ($0.75/lb to $1.25/lb), basalt fibers have properties akin to S-glass. A common use is in the fire protection sector because of its high melt-point.

      Strength-to-weight ratio of basalt fiber exceeds the strength of alloyed steel by 2.5 times and the strength of fiber glass – 1.5 times. '

      http://nextbigfuture.com/2010/08/glass-fiber-and-basalt-fiber-industries.html

      With carbon fibre running at $30kg there should be a lot of potential to reduce weight for cheaper cars - it is all very well for BMW to use premium materials, but not for more everyday cars.
        • 4 Years Ago
        EV,
        yeah, I took a look at the link. I'm betting this has not reduced the cost from $30kg to anything like the ~$2.50 of basalt fibre though. They don't claim they have vastly reduced cost, just enough so that they can make a small profit on their premium cars.
        Good for them, but it would be great to move to something fundamentally cheap and in huge supply like basalt fibre.
        Incidentally, coal accounts for around 95% of all mining, and iron ore almost all the rest, with 'others' as rounding error.
        So get rid of coal by using nuclear, and iron by using basalt, and mining almost vanishes.
        • 4 Years Ago
        David Martin have you ever heard of SGL? Reffered to in evnow's link below.

        "The base for the MegaCity Vehicle is a lightweight carbon-fiber monocoque dubbed LifeDrive. Described by BMW as revolutionary in construction and price, the LifeDrive is produced in a highly automated process developed with SGL Carbon that dramatically cuts costs compared with existing carbon-fiber structures."

        "BMW says the LifeDrive structure is as strong as steel but 50 percent lighter than aluminum."

        AUTOCAR says, "a BMW sources admit that a range-extender version with a 1.0-litre, two-cylinder engine is possible. Using a range-extender powerplant would allow the battery pack to be smaller, saving weight and cost."


        Auto Week says, "It's planned to use BMW's new 1.5-liter three-cylinder gasoline engine."


      • 4 Years Ago
      I am really anticipating what this thing will look like and how much it will cost. I think that I will chose between this and the Fiat 500 when they come around.
        • 4 Years Ago
        Neither EV is out yet, and I actually kinda like the way that the 500 looks. I think that the 2 biggest factors for me will be range and efficiency. If the Megacity is significantly more efficient or has a significantly greater range, then I will choose it. Otherwise, I think that I will end up going with the 500 since it will be less expensive.
        • 4 Years Ago
        The Fiat will be less expensive, the BMW will have better performance, and likely better looking. So it's a trade-off, you'll have to decide if the BMW will be worth the extra cost.
      • 4 Years Ago
      An aerodynamic lightweight mini, sounds like a great ev platform.
      Make the wheel covers flat though.
      • 4 Years Ago
      Go carbon fiber. Perhaps the stuff Armory Lovins has been talking about for years will eventually hit the market.
      • 4 Years Ago
      They claim it will be a cheaper brand.

      "BMW would not comment on pricing of the MegaCity, which is some three years from launch. However, officials hint that the business case for the car is based on sales of 50,000 per year at a base price of 20,000 euros, or about $25,000 at current exchange rates--a little less than double that of the entry-level Ford Fiesta in Europe."

      http://www.autoweek.com/article/20100702/GREEN/100709981#ixzz0sZjPK7zO
      • 4 Years Ago
      It's really interesting for me to see a major manufacturer comprehensively evaluating and designing for composites, and looking at all the potential issues, but also new capabilities that they allow. I'm very much looking forward to see if BMW can pull it off. If they do, I think this has the potential to be one of the bigger gamechangers in the EV scene.
        • 4 Years Ago
        this particular car even if it ends up using carbon fiber wont be a game changer. the use of carbon might later be important but from descriptions it seems a rather conventional car that could no doubt be made with steel and have same specs.

        it looks like they are using it wrong, they are not aggresively pursuing the advantages of the material. we haven't heard talk of a 500kg car weight which is what you are going for if you rationally choose to use carbon instead of just for fashion reasons.
        I like that they are working with carbon but it's like an automaker making an EV, if they don't do it right it'll just be an excuse to not do it again. and BMW has been extremely obtuse when it comes to doing the right thing´and from experience we should fully expect anything green from BMW to be entirely disingenuous.
        also keep in mind that these 'very nice people' are not above blatantly lying and the car could eventually be a steel car with a small gas engine... as Audi did with their 'megacity' A1. they presented it as an electric car but then surprise surprise turns into a completely conventional car. bait and switch.

        as for carbon surface finish, ehh no Sam, carbon fiber composites don't have a fabric pattern surface if you use a mold. and they just might.. not sure what that is about.

        as for the skateboard layout, that's all wrong unless it has depressions in it for the seating positions since it would otherwise add needless height to the car and thus greatly damage the aerodynamic profile. since air drag can be 80% of the energy cost at typical motorway speeds that's rather important.
        if the seats are intended to sit above the battery box that's one of the many clear indications that BMW doesn't really think energy efficiency.
        • 4 Years Ago
        A game changer perhaps in the high end market. The construction BMw will be using is very expensive. because of the brand they can get away with what will be a serious premium compared to a Leaf.
        • 4 Years Ago
        A game changer perhaps in the high end market. The construction BMw will be using is very expensive. because of the brand they can get away with what will be a serious premium compared to a Leaf.
        • 4 Years Ago
        This site keeps truncating my comments today. Grargh.
        • 4 Years Ago
        Turbofrog: Avoid using the "arrow" keys, use the old fashioned terms "greater than": or "less than" instead. The arrow symbols and certain other obscure symbols cause problems on this blog.
        • 4 Years Ago
        I think the fundamental premise behind this project is that BMW is revamping the conventional techniques used for composite construction and working on economies of scale to drastically drop the price of CF structures.

        Carbon fiber bike frames are more complex to manufacture than many composite aerospace components, but can be had for
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