Has anybody got golden rules in how to build a mid engined car chassis. I've seen so many different design that contradict each other. And I've read all the usual books.

Alain, the CLEVER people, start up with a mock up of their car including seats, engine, wheels etc etc etc find the IDEAL
driving position and then make all the suspension compontents including steering rack, steering wheel pedals and ancillaries fit in the available space. In other words the chassis is built/designed around them. If as I suspect u are using an existing body and designing the chassis to take a bigger powerplant u are in a trade off with the available space under the current body, which in a worse case scenario might mean a bit of cut and shut as dicussed the other evening. Have u had a look at the books that discuss rollcentres and suspension geometry yet? Worth looking at them if u have not done it yet, u are putting a lot more power into your wee beastie, things like the C of G and weight will no doubt be a lot different when u change power plant
Shug.

Yeah thought of the lot but I am having problem finding the best structure for the rear end. I would like to build a chassis where the rear subframe comes off and makes working on the engine easier. But I might loose a lot of strength that way. My other problem is the suspension. I am thinking of using double doubel wishbone all the way but is it really worth having inbounds to make the shocks work better or can they be at an angle?

Try using a ladder frame for the engine bay region. Good access and easier to get right than a spaceframe.

If you are using a transverse engine take a look at the Elise chassis. The rear structure consists of a big beam down each side with a stressed seat back and a suspension subframe to close the engine bay region.

A starting point for a kit car version could be to make a rectangle of 4x2 RHS tube to run around the top of the engine bay. Mount the tops of the springs on this tube. A spaceframe to support the wishbones could be added beneath the top tube at the engine bay back and seat back regions along the lines of the Meerkat chassis.

howdy, i thought this might interest you, note how every thing is triangualted and the clever use of tetrahedrons while still leaving plenty of room for the engine.
also remember that most of the forces in the rear will be from the weight of the engine during acceleration and cornering, this will create stress in anything between the engine mounts and the wishbones. and also braking which will cause stress between the engine and the front wishbone mounts (mostly), so bearing that in mind try to tringulate so that the forces are kept in tension or compression between those points (where the weight is, and the suspension components)

also, y or x braces can be added later, and if used properly can efficiently replace welded members.


Russ.

[Edited on 5/1/04 by suparuss]
Rescued attachment russframe.jpg

You could save yourself loads of time and buy the new Barcetta starter kit, its been in development for quite a long time, and originates from Italy - what do you think?

Mark
Rescued attachment Fiat 500 Jolly.jpg

stick a nice bad boy spoiler on and some side skirts an yer away!!
dont like the look of the roll bar though.

oh, i get it, alladin came an parked his magic carpet on the roof!!

Well it is panto season

Oh no it isn't.......

Cheers for the adive. The engine is a boxer 4 cylinder. I think I understand what you mean by ladder. I can't use the barchetta kit as it uses the 126 chassis which useless even with the 25bhp motor nevertheless a 139bp one plus its design for a rear engine car. thank again will keep you guy posted.

Folks,

I came acorss this site today whilst trying out a new search engine (www.vivisimo.com). Anyway, it details an approach, some design decisions and a bit of the basic theory of building a scratch car. Its based around one uni's entry to the formula SAE competition. Anyway, I enjoyed reading it and thought i'd share it.

Have fun,
Introduction to Formula SAE suspension and frame design

quote:

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Originally posted by MikeR
Folks,

I came acorss this site today whilst trying out a new search engine (www.vivisimo.com). Anyway, it details an approach, some design decisions and a bit of the basic theory of building a scratch car. Its based around one uni's entry to the formula SAE competition. Anyway, I enjoyed reading it and thought i'd share it.

Have fun,
Introduction to Formula SAE suspension and frame design

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Welcome to the group and thank you for that very nice link.

Steve Graber

Aye, thats the link. Can't believe it was changed between my posting it and you reading it ..... mutter mutter grumble grumble