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Guest Komodo

New Boy On The Block

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Guest superbad

post-3285-1196102685.jpg

 

This is a shot of the Caterham front suspension (pulled off the web). Ignore the forward lower wishbone mount- it's a single shear mount which is janky. The upper mount is a folded/welded box section double shear mount- that is how you want to do it. Looking at it again, it looks like you intended to draw double shear mounts, it's just that you put the webs 6" apart. Those should be the width of whatever rod end or bushing you are using.

 

Remember that all of the road loads (lateral and longitudinal acceleration) are transferred through the suspension pickups. They should always be mounted at the junction of several tubes (never in the middle of a tube), and every point should always be well braced in all three directions. Your lower mounts in particular are guilty of this- they are both in the middle of a tube and completely unbraced. You've also got a lot of redundant tubes around the engine. Look at how you can clean that area up and make a more efficient structure. Non-stressed engines usually only need one mount on each side, with the transmission mount taking up the third degree of freedom. Engines don't need as much structural support as the suspension. You only need to design for the mass of the engine and the torque it produces, and those forces are far lower than what the suspension sees.

 

And unless it's absolutely, absolutely necessary to do otherwise (or you're being cheap like Caterham), suspension should always be mounted in double shear.

 

On the roll hoop, the way you've drawn it now, it will fail at that top welded joint if it ever gets on its head. That should be one continuous single radius bend at the corners. And you need fore/aft bracing- I missed that the first time.

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Guest Komodo

Some good points there, I will definately take these into consideration. I'm not all that familiar with chassis design at present, kind of picking it up as I go as it's not a taught module in the course.

 

The basic 3d drawing was taken from sketches out of the Haynes "How to build a sports car on a budget" book, although apparently this isn't as comprehensive as I first though...

 

Fore/aft bracing will be added soon.

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Guest superbad

Most of the good books on the subject were published in the 60's. Here are a few good ones if you can find them, just take some of the info on suspensions, tires, damping, etc. with a grain of salt, as it doesn't necessarily reflect current best practice. Tube frame chassis, however, haven't been state of the art since the mid-60's, so that info is still completely relevant.

 

"Racing and Sports Car Chassis Design" by Michael Costin and David Phipps. Costin designed a lot of the early tube frame Lotuses (including the Seven I think), and he's also the "Cos" in Cosworth. This is probably the best book I've ever read on tube frame chassis design. There are a few used copies on Amazon, but they're expensive. A good engineering library in the UK should have one (I think Loughborough had it, maybe they will send one down on loan?)

 

"Racing Car Design and Development" by Len Terry and Alan Baker. Terry was another Lotus designer. This book covers systems more than the chassis itself, but it's still a good read.

 

"The Sports Car: Its Design and Performance" by Colin Campbell. Focuses more on 50's road cars. I don't think there's much in here on tube frames, but it's pretty interesting.

 

I think I may have a few others in storage, I'll see if I can dig them up.

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Guest Komodo

I shall check out that Mike Costin book, just joined up to the IET, so have access to their free libarary of 70k+ engineering books... I'm sure they'll have it in their somewhere.

 

I will point out now that the chassis design module is only a short one, and is not intended to be an extensive design project like the engine is. Most people in my class are focusing on smaller parts of the suspension, but I fancied challengeing myself to something a little more comprehensive, hence having a pop at the whole chassis.

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Guest Hallian

Looking at your engine block there's a lot of sharp edges and big wall thicknesses differences. I would put plenty of rads in there otherwise you'll get lost of stress concentrations and shadows when you come to do your FE work. Also go for uniform wall thicknesses where you can - differential expansion of the different material sections will distort the block and your cylinders.

 

Hillier's fundamentals of motor vehicle technology is a great reference book for all aspects of vehicle design, and its quite cheap too.

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Guest Komodo

Another good point. At present the block isn't really part of the development project, my project is purely to optimise this design of engine for a performance road vehicle, the company currently building the prototype is focusing on aircraft engines.

 

Never the less I'll look into improving the block design. I have a copy of that Hilliers book sat next to me as it happens!

 

Here's a few of the latest renders, many things are far from perfect I know, but it's getting there within the 6 hours a week I spend on it!

 

post-17737-1197233524.jpg

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Guest Lilith

i have no idea about engines :blush: but seems that theres a lot of work you have done there, modeling looks very diffcult to me

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Guest Komodo

To be honest it's only basic modelling techniques that I've employed in this, there's no complex surfacing stuff A) because I don't understand it and B) the nature of the design doesn't really require it.

 

It's fairly simple stuff, just a lot of it. :)

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Guest hairius28

have you considered using the COSMOS Xpress analysis wizard on your spaceframe? i love that thing, makes it bend! anyway its probably quite useful when designing stuff like this.

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Guest Komodo

I dout I'll be using COSMOS Works add in on the chassis as the module isn't that heavily based on the actual 3d design, more the overal design process, marketing etc.

 

I will be using COSMOS Works extensively to test the engine however, as that is a far more involved product.

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Guest Komodo

A quick update on the chassis.

 

I've decided o junk the previous design and go for something ultimately light weight and performance orientated. The new design is a single seater, mid moutned rear wheel drive layout. This chassis was drawn up in the last two days, so I know it is far from perfect, the suspension in particular will need a lot of detail added. Whats here is the basic require to have it all function as suspension should.

post-17737-1202347629.jpg

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Guest Impatient Pete

Wow! So much progress from your first post! very nice.

I don't know much 'bout cars, but I see some potential here...

 

Pete

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