Make a new monocoque for a modern vehicle
 

I wasn't entirely sure where to post this due to the mutiple angles it can be pitched from, so I posted it in the most frequented related forum.

Caution: The following post is in metric

Once upon a time I came across an almost unique construction method in todays world of making a structural monocoque out of honeycomb panels, then covering this in foam and sanding it to (the arguably attractive and certainly aerodynamic) final shape.

Detailed here
Honeycomb Monocoque Chassis
And here
Polystyrene Body

The key points are that the 3 wheel two seat chassis (with one door) weighed in at 32kg, the painted body 22kg, and the acrylic canopy 10kg. That's just 64kg... (The complete electric vehicle weighs 300kg) and the whole construction can be done at home...

The author of the articles estimates that a similarly constructed body for a 4 wheeled car with no roof coming in at 150kg...

So my plan was to take something small, late model, and cheap, and construct a new open-top chassis for it, using the same suspension pickup points.

A 2009 Suzuki Alto weighs in at 880kg, and has 50kw to its name. It also conveniently has acceptable handling (yes I have driven one), passable performance, exceptional economy, cheap available parts, and all of those fancy acronyms that people like to see (abs, stability control, electronic brakeforce distribution, etc etc).

By making a new body with the above method and fitting it with the alto mechanicals and installing the bare necessities (basically some lightweight seats and a few marine grade guages and stereo bits) I could see the complete car coming in at 500kg.

This gives a power to weight ratio of 100kw/tonne (as a comparison the alto has 57kw/tonne stock, and a Toyota Aurion has 125kw/tonne).

Of course the benefits are also found in braking, cornering, and efficiency.

If you wanted to spend more money and weight you could opt to rip the heart out of a new Swift Sport (100kw, 1050kg, 95kw/tonne). This would probably up the vehicle weight to 600kg (extra cylinder, extra gear, bigger wheels, bigger brakes, and heavier duty suspension) but the power to weight ratio would be a needless 167kw/tonne.

So have any of you done this? Essentially re-bodied a car with an arguably advanced lightweight chassis?

Plenty have done spaceframes with mix and match suspension, but I haven't seen a single kit car that uses one donor vehicle for ALL mechanical components, and I also haven't seen a kit car with a chassis like this.

I want a fwd spider...

this is kind of what i'm building.

i'm making it a lot simpler then that however as i'm not very smart and complicated things confuse me.

I'm going steel tube frame chassis, nice stout fiberglass body, laminate glass windshield, honda car engine, transmission, hubs, tires, etc.

should be under 1000 pounds for a 2 seater, enclosed with heater and air conditioning.

In the land of the blind, the one eyed man is king.

Check into aluminum honeycomb used in aircraft construction. Keith Noakes did a couple good books on composite construction. Fenders can be made of ABS plastic; see the paper model software for making the skin. Use automotive glass and suspension parts. Design around a ratio of 36 lb per horsepower for gross vehicle weight. If the seats are slightly offset front to back the vehicle can be made narrower. Pay particular attention to locating the set belt anchors.

36lb per hp? That's around 45kw/tonne. I couldn't live with that, especially not in a car that's going to be styled as a sports car. Where did you get that number from anyway?

I like the reverse trike layout, but I can't get excited about tandem seating. Anyone who's ever sat second on a motorcycle knows what I mean... :(

A side-by-side version would weigh very little more and provide full fun for two. maybe something like what VW or Peugeot did, but using the DIY approach exemplified in the article.

http://gothamgarage.files.wordpress....3/vw-trike.jpg

http://www.dpccars.com/photos/01-31-...ugeotTrike.jpg

The Alto's a good choice. Just finished a week in one and managed to get 55 US mpg in mixed cycle driving merely by driving with a light foot. (Didn't get a chance to record accurate figures for engine-off P&G). Heard tell that at a steady 50 mph, 70 mpg is possible. After that drive, I believe it.

One of the main factors limiting good economy in the Alto on the highway are the poor aerodynamics and short final drive. With a lighter, lower body, you can give it a much longer final drive (perhaps bigger drive wheels will suffice) and keep the same performance.

Probably better to simply start rebodying the car as it is... replace body panels with composites, lighten seats and seat frames, and etcetera... lower the car, give it skirts... lower the roof a bit to make it less vulnerable to crosswinds... lot you can do with a car whose body is almost inconsequentially light, as it is.

Very nice material/process links.

Do you know about Monopan?

MonoPan :: About MonoPan®
http://www.monopan.ca/images/diagram.jpg

Have you ever stripped a car, I mean completely stripped a car down to the bare monocoque steel shell? My 1978 Porsche 911 weighed approx 300 lbs (136 kg) when everything was removed. The heavy bits like the suspension, brakes, wheels, engine, sound deadening, bumpers, cooling system (water, or oil in the 911 case).

Just keep in mind that what is bolted on to the shell is what makes the vehicle useable, but also adds a very significant amount of weight.

I have been thinking about something similar, but on a small 4WD chassis, something like a Suzuki Samurai or Honda CR-V. I drive on a lot of really rough dirt roads, and would like something that gets better than the 27 mpg I've been getting from my Toyota pickup, and which has comfortable seating - by which I mean semi-reclined, not bolt-upright like most 4WDs seem to have. So I might wind up with something like a sports car with about a foot of ground clearance...

Anyone done anything like this?

I built a single-seat electric car out of aluminum in high school, and the frame probably came in at 10kg. The lead-acid batteries, motor and controller were a significant portion of what I estimate was a 100kg total weight. It had no suspension and used custom made bicycle wheels...

Anyhow, I'm never impressed with 2-seater cars. I can get 60mpg on my CBR600 and transport just as many people and cargo. I can do all this for $3000 and have 110hp to play with. For less money you can get a Ninja 250 and get 100mpg.

Neat to see the design process, but car of the future; certainly not.

The 36lb/hp came from an article by SAAB engineers in the 60's as the optimum weight for a passenger car. In a sports car that would be lower, as in the old SAAB Sonnet 4 cyl. fwd. Richard Ridley sells plans for trikes that could be adapted to a moncoque design.

The 4 cyl. dune buggies have 24" suspension travel. Seat angle will depend on the suspension and muscle tone of the back. See Mark Martin's exercise book.

Get something like this:

Welcome to the Trail Tough Products
http://a6.sphotos.ak.fbcdn.net/hphot...33655773_n.jpg
CRAWL/Trail Tough Zuk Build « CRAWL Magazine

and change the windshield angle.

But knowing a bunch of Samurai owners... I can tell you that fuel economy is not a strong point. Not with that heavy 4x4 system mated to a tiny, carbureted engine and short gears.

That's almost exactly opposite to what I want. I don't want the suspension & wheels jacked up beyond stock, and I want the distance between roof and frame/floor pan to be much less. Think of a late-model CRX on a 4WD chassis...

The difference between me and those Samurai guys is that they're driving their 4WD as recreation, while I want a vehicle that's a tool to get me to the trailheads. That generally involves some highway driving - anywhere from a couple of miles to a couple of hundred - plus a last 2-5 or so that are usually very rough dirt, and often climb 1000 ft or so per mile.

The idea is similar... scrap most of the body and pare the vehicle down to the bare minimum. And a Sammie is about as minimal as you can get. Keep the stock height, pull the body off and make your own. Unfortunately, most aftermarket bodies I've seen for the Sammie/Jimny chassis are completely non-aerodynamic tube-frames like that one. You'd have to find a way to make it more aerodynamic.

You could always just slap a CR-X or VX shell over a Sammie. Since those things are ladder-frames, the body itself doesn't serve much purpose (which is why so many people convert them into buggies).

My 1978 Honda Hawk and 1986 VW Golf Diesel both could get 50 mpg hwy, but I would not confuse the two. A motorcycle is a motorcycle, and a car is a car.

lol

I did not mean to take a swat at anyone.

You just could not get me back on a bike, too many text messages leaving people driving blind these days.

If you have ever had freezing rain coat your helmet visor with ice while driving at night, you would agree that a motorcycle has a limited usability envelope.

The things I have lived though to tell about....................