The donor vehicle

Posted on December 6, 2007


Originally, I thought of buying an old car and use it for this project. I even promised my nephew I would buy his Seat Marbella (sorry, Rodrigo!). This had several advantages, among them being the facts that it was cheap, I could choose any kind of car I wanted (a light one, for sure), and it wouldn’t stop me from using my own car if I needed it during the hardware modification phase.

Then I got greedy. 🙂 I thought that using a really old car (2 or 3 “generations” behind the current market status) to showcase innovative technology was… plain stupid. In other words, most of the stupid people out there would be “stuck” to the aesthetic aspect of the project, and would not take it seriously for the true value it contains. And, unfortunately, there are way too many stupid people in powerful positions out there, so I can’t ignore that audience. 😉

Besides, nothing would make me more proud and happy than to convert my beloved everyday car into a better thing. It has served me very well for 9 years, and it is still not technologically obsolete or physically falling apart. And I know it really well (in both the driver handling and mechanical maintenance aspects), which helps in the conversion process.

So which car is it? It is a 1998 Mercedes-Benz A140 (a.k.a A-class). It’s got a 1.397 c.c. gasoline engine, supposedly generating 82HP at 5.000rpm and 130Nm at 3.750rpm, but I seriously doubt it. 😉 It weighs 1.020kg when ready to go (full tank), so it’s a little bit on the heavy side for a compact commuter car. The aerodynamics also sucks above 140km/h. The worst part is that it drinks around 10 Liters per 100 km (25 Miles per Gallon, for our imperialistic friends), which is way too much gas for my taste. Considering we have seen wonderful things such as 3L/100km (80MpG) in some recent cars (although lighter ones than mine, and Diesel-based), I would say that I would be quite happy to reduce mine’s consumption to half. For starters, of course. 🙂


(Picture shamelessly stolen from some online dealer, I forgot which)

The A-class also has a distinctive feature that I expect to make use of: the “sandwich” concept chassis. It was introduced in 1997 as a way to make a small car just as safe and comfortable as a big car. They made a car that was about 20cm taller than average, and with that extra space under the passenger floor they placed all the technical systems in a new disposition. As a result, this car is very safe in crash scenarios because there are no edges near the passengers and the contents of the engine compartment never penetrate the passenger compartment. It also provides a perfectly flat floor that makes this car extremely flexible in its roles. I’ve personally fitted in 3 adult-size mountain bikes, 3 loaded camping backpacks, and 3 adults comfortably sat, after removing the rear double-bench for one specific trip. With all doors and windows safely closed, of course. 😉 It can also double as a light pick-up truck, if you remove both rear benches (to help moving some furniture from time to time).

More interestingly, this extra “sandwich” volume has proven to be able to carry a multitude of technical systems. Among the most prominent examples is the “Necar” series of experimental fuel cell vehicles developed by Daimler-Benz itself. Since early on, they’ve been cramming the whole hydrogen storage, conditioning, and processing systems as well as the fuel cell itself and auxiliary systems under the floor of the A-class. The latest generation, the “F-cell” Mercedes, is circulating in a number of small test fleets around the world. These cars pack around twice the normal volume (and weight!) of technical systems, and yet they have the same internal passenger space as any other. Very sweet engineering.

(Picture shamelessly stolen from

Even more interesting, once upon a time in 1997 there was an Electric Vehicle version of the A-class (shown above)…. which got killed away and swept under the rug just like the GM-EV1, to give way to the eternal promise of the new hydrogen economy. I’ve tried finding it in the Mercedes web site, but I can’t. Maybe I’m looking in the wrong place…

Anyway, this all serves to say that I expect to find enough space in the car to fit the batteries and electronics without sacrificing passenger comfort or safety, or even drive handling. Actually, the drive handling should improve, because the weight distribution will be better (if I can have my way with it, of course). Spreading the batteries around under the floor should yield a more stable vehicle.

Still on the subject of space, where does the electric motor go? It’s going into the wheels themselves. One of the best features of electric motors is that they can be fabricated in many different sizes and shapes. The logical option is then to include the motor inside the wheel itself, saving the weight and losses of a mechanical transmission (clutch, gearbox, axles, differential). It does have the downside of increasing the “unsprung weight” of the wheels, therefore making the suspension less effective and the car a little less comfortable, but since this is not a performance car, I don’t think adding 10 or 15 kg to each wheel will be such a big thing.

Besides, having motorized wheels opens up a whole new set of possibilities: we can load the electronics with all kinds of control programs, expanding the already commonplace ABS/ASR/ESP systems. If we have all wheels motorized, we can also select between 4-wheel drive, 2-wheel front drive, or 2-wheel rear drive, according to driving conditions (for example). Hell, we’re just getting started here. 🙂 In fact, if you don’t mind losing a little rubber, you could actually make the car turn on its axis, just like a tank! That would really come in handy for some old city parking spots… 😉

Posted in: Add-On-HEV, Strategy