Hey folks, am about to start sourcing my donor car, thought I'd introduce myself here and let everyone know what I'm up to in the hope that some idiot has attempted some of my plans before. I've decided on a few build priorities, anyone else have these directions in mind, or have been down this road and had problems or successes?

1. BMW 3-series donor, 2.0 six pot or 2.5 if it can be shoe-horned. Gorgeous engines, bombproof mechanicals. Will be tricky though as untrodden ground, and electrics might prove problematic. Will be building chassis 2 inches wider anyway so track and engine size should be acomodated.

2. IRS - wishbones, drawing from the rorty design and some others that have appeared on the net. Have been looking into the maths, and looks like all the designs out there have a centre of roll far lower than the centre of gravity. This probably doesn't notice much as the springs are usually very hard on a locost, but unless I'm mistaken (which is far from unlikely) i think this is unfavourable, so I'm going to have to play with it. Would really like to build with alu uprights and maybe look at alu wishbones too(any experiences out there?). I've heard tell that the early rx-7s had alu uprights which can be made to work with locosts - anyone know about this? What with all those rotarys seizing there should be a few about.

3. Integral roll cage in chassis, ie the A-pillars which normally only to hold the glass will have some strength to them and be attached by a central spine to the rear rollover bar. Also some modification to the side bars for some hint of side protection. Not for being broadsided by 40 ton artics of course, I'm thinking more lamp-posts or armco when i spin the thing. Mybe it's a new-dad thing, I dunno. Worth a 50kg penalty though to my mind.

Before everyone floods with replies like "this is going to take you until you die..." yes i know this is a long haul and not the easy path! For me the designing and building is really the point. When i finish this I'll be bored and it'll be time to build my boat, if i'm not already senile.

Ok, couple of points fairly at random :-)

RHD or LHD car ? Because, the BMW engine is well on it's way to being a slant six - there may be issues with your steering column if your are building a RHD car. (Although Marlin have managed it in the past.)

Mazda RX7 based car - although still using the rotary engine can be found if you click THIS HERE LINKY

On the road for a long time now and through a lot of development so well worth reading.

Thats all for now...

do a search on roll centers, i think they are meant to be lower than cog. Good handling production cars have them quite low. For instance, look up the elise's centres.

http://www.locostbuilders.co.uk/viewthread.php?tid=11341

[Edited on 1/7/06 by JoelP]

1. I have a 2.0 BMW engine lurking in the garage, waiting for me to finish (actual start) with the frame drawings. Engine and gear box is well within 10 kg of a pinto and a type 9 so weight is no big issue. It might be a little tight in a book frame length wise, but I believe it is possible. Real drawback is hight, at least my engine have the oil pump at the bottom of the sump. As far as i can tell, no way to shorten it except by a dry sump. I'm dreaming of a s-box, 1:1 in fifth gear

2. RC calculations is a rather theoretical (and on this board somewhat sensitive) subject. My opinion: check that it's reasonable but don't get hanged up on it. I believe matched CG and RC went out of style some 50 years ago but might be wrong.
Alu wishbones are extremely hard to dimension correctly. If you are building a racer with an expected life span of one or two years and total checkups every week, it's ok but for a road car, forget it.

3. Unless you expect a member to take a direct hit, increasing dimensions isn't that effective. Better triangulation to spread the loads, is a lot more favorable.
Make yourself a real side cage/bar, any thing hitting the side bar (N) have properly hit you before.

You will manage a build like this, in time
First try on something new usually turns out a little below par so I recommend you to plan two builds. One fast and cheep, to gain experiences, try out technique and getting an understanding of what you are doing. Then the real one, with all the bells and whistles you always dreamed of.

Happy building!

re: roll centres , maclaren etc were still using them as a checksum at least 10 years ago .

westfield ones are all over the place !!!!

its more important to control the direction t moves under cornering than static ones .

with a +442 chassis the BMW stuff will fit , and dare i say it again and again try a volvo out for size , its cheaper and easier to fit the live axle at the back and use the struts cut down at the front .

For some reason Volvo based builds are pretty common here in Sweden. SAAB engined builds too (250-300hp )

This is principally a Volvo 740 and some steel pipes. Frame is +3 5,5 2 as it was going to be more Morgan/Marlin style, but that has changed, now it looks very 7:ish. Not quite finished but very drivable in this pic.
[img][/img]

got any links to a website ?

is it a turbo version ?

Blimey - 24 hours and so many replies. THis is a seriously active forum. I wonder how many divorces have sited ron champions book as adequate grounds?

Particularly interested in those replies about the rear COG/COR. I had hoped it wasn't the main priority, as that pointed toward a complete redisign when i'm hoping to plagerise a fair bit!

Leto - is that the six cylinder 2.0 bmw, or a four? Part of the attraction for me is a six... Also is it all iron or half ally?

Point taken about the side impact, though I'm not sure how you could triangulate in any way that's going to stop deformation into the passenger cabin in any meaningful way without increasing the width of the sidewalls substantially, by which time you have reinvented a caterham 21. Anyone know of examples of anyone trying?

Cheers folks!!

Volvorsport
No turbo, no real website, but a few pics here.

This site is about a locost Volvo turbo build, but it is all in Swedish, there are however, a few hundred pics so you might find something interesting anyhow.

jlparsons
Half ally six, was looking for straight 8 but the all ally ones are hard to find

Quite right, you can't triangulate the side in any meaningful way. I was on to something more along this line but didn't express myself to clearly. The side bars are bolted and can be removed.

Side Bar

I've seen that rx-7 based car before, think i read through the build diary a couple of months back. THat's a lot of fresh air under that hood! Looks a good build. Have been very attracted to the rotary thing, really suits the ethos of the car, with lack of torque no bother for a superlight. Only the lack of reliability (or i guess the level of upkeep required to maintain reliability) make me shy away from the rx-7. When Rx-8s start turning up at donor car prices, that might be interesting. (has it been done already...?)
For now a bavarian straight six, preferably a half-aly, looks to me a fine choice, especially when the tweaks i'm thinking of are going to put some pounds on.

Aly wishbones - I'm assuming that the ones with the longevity concerns are superlight race versions? Lots of production cars get away with all aly linkages, I'm thinking that if I don't go to silly on the weight saving i might be able to create something long lived. Aly does have that pesky tendancy to fail after exactly X repetitions though, which bugs me. As you can see I'm still in two minds. Still, that's relatively few for me.

The automotive industries has a few advantages. Seasoned designer with a lot a FEM power, experience from experimental cars and a good hunch on what load spectra different kind of vehicles can expect to endure in there life time. The last one is the key, if you have the right load spectra in your hand the rest is mathematics. Without it you can guess and have opinions, so can I, Bob at the corner and your old aunt.

And to repeat myself: go for two builds, one fast and simple and one advanced. That way you can have several minds at once

[Edited on 06-7-2 by leto]

I do see what you mean with the two-builds thing. I'm planning kind of the same thing - the car will at first be a mule to test everything I want to try out. When I've finally completed/broken everything i've come up with, I'll use the same chassis if still applicable to build up the final car, or build again from the ground up if necessary. Hence a long development, but that's the point. Also I've got no room to do two at once.

For the aly wishbones, I must confess to a slight cheat - a father with 30 years designing auto suspension. The aly suspension will be something of a joint project! He's always been tempted to build himself a car, but my mother always vetod him. Have a feeling he'll be over quite a bit while I'm building mine, which of course I'll do my best to encourage.
I shall build the car with steel wishbones first of course and get everything set up, then worry about the aly later.

RE: Ally suspension in production cars...

For cost reasons production cars are restricted to mass production methods like casting and forging that produce really heavy over engineered components. In this case the switch to forged solid aluminium can save weight whilst still giving a part that is over engineered enough to last the life of the vehicle.

In Locost land we already use lightweight fabricated tubular wishbones. A thick forged ally wishbone would likely offer no weight advantage over a fabbed steel wishbone. A tubular welded ally wishbone is not analogous to the use of ally in production car suspension and is rather dodgy territory.

Look to motorsport for lightweight design with no budget restriction. You wont see a single welded tubular ally wishbone for good reasons. Instead they will use thin guage alloy steel, titanium or composites at the top end. No ally, and if those production car manufacturers that want to save weight had no budgetry concerns they'd use fabbed steel/titanuim too in favour of big ally forgings.

Liam

some of the big GT cars use CNC machined alloy for wishbones .

even volvo use alloy in there later cars for bottom wishbones on struts .

I do see your point Liam, aly welded joints are very susceptible to fatigue hence very few aly tubular wishbones about. Many manufacturers make great use of pressings though, either bolted, spot welded or bonded, and make great weight savings. I think i can get away with a lower weight on an aly tubular tho, cos I've got some tricks up my sleave when it comes to the joints which wouldn't be feasible on a production car.
We shall see! Worst it can do is mean an undignified limp to the side of the track, which i think any locost builder worth his salt has to experience en route to a finished car.

quote:

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Originally posted by jlparsons
I do see what you mean with the two-builds thing. I'm planning kind of the same thing - the car will at first be a mule to test everything I want to try out. When I've finally completed/broken everything i've come up with, I'll use the same chassis if still applicable to build up the final car, or build again from the ground up if necessary. Hence a long development, but that's the point. Also I've got no room to do two at once.

For the aly wishbones, I must confess to a slight cheat - a father with 30 years designing auto suspension. The aly suspension will be something of a joint project! He's always been tempted to build himself a car, but my mother always vetod him. Have a feeling he'll be over quite a bit while I'm building mine, which of course I'll do my best to encourage.
I shall build the car with steel wishbones first of course and get everything set up, then worry about the aly later.

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