Hi guys and gals

I have been doing tons and tons of research on the ultimate middy road-going sports car for a while now and only recently have I thought of using carbon and glass fibre in my chassis. Maybe a front tubulalar section for suspension that bolts onto a carbon/glass fibre mid/passenger section (kind of like a reinforced bucket) that bolts onto a rear section that houses the engine and rear suspension.

Has anyone here ever attempted one of these possibilities or am I a bit off track again?

I want to make my car as modern as I can, and try to incorporate different materials. If theres anyone looking to go this route, I'd love to chat and exchange info.

Very advanced for many on here but there are a few others doing similar to what you plan.

You might like to have a good read here for inspiration.

certainly possible .

i was going to do that until i got side tracked .

Cheers Paul. I have come across the DP1 already. very well refined design he has there. Still uses a tubular frame throughout though with a carbone fibre shell. What I am looking for is info on how strong the carbon/glass fibre chassis are and if anyone has tried it, is it costly? Recently, carbon fibres' popularity and newly found manufacturing processes has brought down the price a bit, so its kinda in reach. This is from a South African context

Volvo sport

Have worked out anything in the process? ...design, costs, strengths???

I hate to burst your bubble, but carbon fibre is a bit more complicated to make good strong bulkheads and the like.
The technology that goes into them to make them strong means using other fibres, weave patterns and an autoclave big enough to remove all of the air.
Unless you have a bottomless wallet or your dad owns Maclaren, I think you should give it a miss. (at least for structural componants)



[Edited on 7/4/2008 by nitram38]

Unless you have significant experience of this type of construction I would advise against it. I tinker with carbon fibre/epoxy moulding and have done for many years. Carbon fibre can provide impressive stiffness for a given weight but the impact resistance is less than impressive.
Most exotic composite race cars are built using aluminium (or similar) honeycomb materials faced with carbon fibre and any moulded parts are generally made from pre-preg which helps achieve the optimum resin content with a panel containing 4 or 5 layers of carbon fibre measuring less than 1mm in thickness. This type of moulding requires the use of an autoclave to cure under elevated temperature and pressure. It is possible to cure in an just in a programmable oven but my one attempt at moulding pre-preg ended up with me achieving my strongest bond ever. Unfortunately it was the bond between the part and the mould (even using proper chemical release agents)! Oh yes, and pre-preg usually needs to be stored frozen.

Nitram38,

thanks for the comment. I have worked and designed for a fibreglass mould and plug manufacturing company. Guys that worked in the factory told me that carbon fibre is worked in the same way that GRP is. I know that Huge car companies use ovens to cure them and machines to extract air from them. But, the same basics apply to GRP and carbon fibre.... Apply resin, then the mat, roll out air bubbles then repeats these steps for another layer. I have come across a site of a kayak manufacturer. He uses carbon fibre in that same way

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Richard Quinn

Unless you have significant experience of this type of construction I would advise against it. I tinker with carbon fibre/epoxy moulding and have done for many years. Carbon fibre can provide impressive stiffness for a given weight but the impact resistance is less than impressive.
Most exotic composite race cars are built using aluminium (or similar) honeycomb materials faced with carbon fibre and any moulded parts are generally made from pre-preg which helps achieve the optimum resin content with a panel containing 4 or 5 layers of carbon fibre measuring less than 1mm in thickness. This type of moulding requires the use of an autoclave to cure under elevated temperature and pressure. It is possible to cure in an just in a programmable oven but my one attempt at moulding pre-preg ended up with me achieving my strongest bond ever. Unfortunately it was the bond between the part and the mould (even using proper chemical release agents)! Oh yes, and pre-preg usually needs to be stored frozen.

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oooo glass fibre chassis....you been peeping

fo9r the cost associated with it you may be better looking at aircraft grade ali? then again maybe not. im sure someone will know more than me

I'm not wanting to p*ss on anyone's chips but even something like a fairly standard West epoxy laminate really needs to be vacuum bagged to get a decent strength to weight. It also needs to be cured and post-cured at a higher temperature than a polyester resin to achieve full strength.
It isn't a black art (well, I suppose it is black and does look nice!) but if you are looking at a basic wet lay up then I certainly wouldn't do it for anything structural/safety critical

I'm using fibreglass to make mine but using something groovy in the ingredients to add stiffness yet weighs nowt...

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Triton

I'm using fibreglass to make mine but using something groovy in the ingredients to add stiffness yet weighs nowt...

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Loads of blue smarties, hardest bit is eating all the other ones first..and doesn't matter then if car isn't any good as will be too fat to get in it anyway..


Seriously it's not that new but it is for a car so if i write it here do you promise not to let anyone else read it?....

Gakes,

u2u'd you meduck

Mark

Doesn't anyone build a car for 250 anymore?

www.darrian.co.uk

thanks guys.

Triton, I U2U'd u 2 mate. This must be one of the greatest forums if not the best ever. So much knowledge floating around.

Has anyone made any progress on the 3D model hosting or something? I have a few models I dont mind sharing

Is it a layer of sandwiched foam?

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Originally posted by Triton
Loads of blue smarties, hardest bit is eating all the other ones first..and doesn't matter then if car isn't any good as will be too fat to get in it anyway..


Seriously it's not that new but it is for a car so if i write it here do you promise not to let anyone else read it?....

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the other thing you can use is parabeam .

its used in grp pressure vessels , and can be used with normal resin .

or a couple of sheets of teklam to get you going .

do a google .

The new smartie tubes are just right as nice shape and glue together easily. Like i said before the down side is the amount of munching to get said tubes is a pain but needs to be done.
Place the odd blue one for right affect and bingo....only smarties have the answer!

But that might be all a load of gobbledygook for all I know...it may well be the yellow ones needed...

From the sound of it, what you would like to build is the same basic design as the Mclaren SLR (our sister company builds them and the Koenigsegg - damn they look fine in bare carbon!). The design that goes into the tub is vast. When you think of using composites, then you need to consider so much more than just the material choice. CFRP is a wonderful material, assuming it is processed well, and used correctly in a well engineered design. The geometry, the material, the thickness, the process etc etc etc can all play a massive role in determining the final strength/stiffness properties.

It is by no means impossible for an amateur builder to design and manufacture something really effective (I think Syd Bridge has done something similar in the past?). But personally, I wouldn't. As you cant design, test and redesign, you would need/want to over engineer it to be on the safe side, then you may find other materials would have been better to work with.

There are a number of hillclimb cars made of pre preg carbon fibre that were designed and manufactured at home. A lot are done using vaccume bagging and elevated cure, not under pressure in an autoclave.

There are a lot of them that have survived being attacked by moving tree's / crash barriers without significant injuries to the drivers.

Personally i think one of the biggest problems will be getting decent quality carbon, at a sensible price, in a sensible time frame. Its too popular.

Years ago I read an article in a motoring magazine about how Morris 1100's were made in GRP for sale in Spain (I think). I've Googled it but there doesn't seem to be any references to it anywhere. It wasn't an April fools joke, the article was supported by a number of pictures showing the mould making process. As I recall, the whole car was made of regular fibreglass and polyester resin. There were a few kits in the 70's with fibreglass tubs too I think. There's no reason why a fibreglass tub wouldn't work. Special attention would have to be paid to areas of high stress but it'd be perfectly feasible. The main difficulty you'll have with it is getting it past the regulations. A tubular space frame has much more easily calculated strength. As otheres have pointed out, the way a structure is made with composites and the techniques used will have just as big an effect on the final strength of the finished part as the design itself.

Don't forget, you're the crash test dummy in the equation.

Like I said before, this must be the best site ever. Anything is possible and this forum has all the right members

I thought it was possible, not just wetting myself How does the vacuum bag work??

I have books on building boats, it covers Carbon & Kevlar amongst a whole heap of other materials. It's very interesting to see just how many down sides there are to these materials which are not often mentioned, Carbon especially sounds a right disaster in a crash (virtually turning to dust in impacts) unless used in a honeycomb panel like in F1 etc.

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It is by no means impossible for an amateur builder to design and manufacture something really effective (I think Syd Bridge has done something similar in the past?).

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It is possible to buy both fibreglass skinned honeycombe panels and carbon skinned honeycombe panels in any thickness from a firm called 'Technical Resin Bonders'. These are easy to cut and can be bent within certain limits, and joined with adhesives and carbon cloth reinforcement. Great construction materials for stiffness and light weight if a little on the expesive side (an 8' x 4' carbon skinned honeycombe panel is around £900).

Hi Gakes,

My design was started with this in mind, and it is still something I am exploring. The biggest problem seems to be getting through regulations as you have to prove to them that your design is strong enough. Something that was suggested to me by one of the SVA people was that when I create any stressed part, I create a 2ft odd square piece from the mould then show it being loaded with comparable loads on the bench, so you don't have to destruction test the entire structure! They will also expect to see FULL photographic evidence of layup methods, including mid-lay on areas that include structural re-enforcements such as seat belt and suspension mounts.

Information is not exactly free flowing about how to go about this - I was being helped by a large supplier I was going to purchase all the materials from, but they then went very quiet... now I'm left with half a design and some help from guys on here!

If you are looking at carbon, you'll also be wanting to look at kevlar in the mix to provide impact resistance in critical areas as well as honeycomb or foam for stiffness. I'm considering a dense foam that is used in the F1 race boats - as the supplier said to me, if it can sustain repeated loaded impacts with a high swell sea at 100mph+, it'll withstand most things!

Autoclaves are not necessary, a vac bag and elevated temp cure appear to suffice. Currently my plan is a mix of carbon, kevlar and honeycomb panels, with metal inserts at critical load points, so I've made as many surfaces in the tub as flat as possible, held apart by curved areas to provide geometric strength. Unfortunately I haven't got a brain big enough to do structural calcs so going to do some test parts!

Vac bagging is as simple as it sounds - stick the entire laid up part in a large poly bag, seal the end, stick vacuum tube in bag. The vacuum machine itself isn't any old dyson though, you'll want a high capacity pump that is capable of sustaining a strong suck. I actually run 2 pumps - one is a very high volume to quickly evacuate the majority of the air, the other is low volume but capable of almost -1 atmosphere pressure so does the pressure bit well.

[Edited on 8/4/08 by Delinquent]

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Originally posted by D Beddows

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It is by no means impossible for an amateur builder to design and manufacture something really effective (I think Syd Bridge has done something similar in the past?).

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Errrm I'd hardly call Mr Bridge an 'amateur builder'

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Originally posted by Mr Whippy
Carbon especially sounds a right disaster in a crash (virtually turning to dust in impacts) unless used in a honeycomb panel like in F1 etc.

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This is a thread on GT40s.com of a guy building a carbon GT40.

http://www.gt40s.com/forum/gt40-build-logs/24086-carbon-gt-mono.html

His day job appears to be making aerobatic aircraft, and he appears to know what he's doing. Note the lack of autoclave, plywood forms and vacuum bags seem to be good enough for the job.

I suspect the hardest part of doing this sort of job properly is amassing the knowledge to do it properly.

Gakes, you should really check out what Dennis is doing now with his DP1.
Rescued attachment dp1365.jpg

The thing that scares me about CF is that you can't easily tell when it has been damaged. Or badly cured for that matter. The aerospace industry employ various forms of non destructive testing, which are not available to mere amateurs. Am I missing something, or are there locost test techniques? Or is the risk engineered out by using high safety margins? Does anyone know why Westy give up on the CF chassis? Dennis P must have hit that issue too, so maybe he has discovered a solution.

Presumably GRP chassis suffer from the same problem. Lotus built a GRP chassis on the first version of the Elan in the early 60s. They seemed to abandon the concept but wasn't the Clan Crusader a Lotus design (that may have been a PR fib of course) - that had a GRP chassis IIRC. I guess Davrian and GTM must have resolved the issue, at least sufficiently for SVA purposes - does anyone know how they do it???

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Originally posted by PukI guess Davrian and GTM must have resolved the issue, at least sufficiently for SVA purposes - does anyone know how they do it???

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Sound.

Tap test with a coin. Where there is delamination etc you can hear the change in sound. F3, Formula renault, teams etc make use of this technique.

If you were being fancy you could use ultrasound to check it, although youd get reflections at every change in section and material. but i guess you'd be looking for relative changes in the response spectrum.

At a guess they stopped selling them as they were so expensive and no-one bought them. It was designed by martin ogilvie im led to believe.

[Edited on 8/4/08 by jono_misfit]

thanks guys,

Delinquent, very well explained and shows a very good understanding and lots of research!Bravo my friend, keep it up. we should be doing these leeps of faith to keep us progressing.

Dzine, that is exactly what i am thinking of.its simple, stiff and superlight.

I started making a pipe roller today and will post sum pics of the progress soon.

Go for it

It's easy to say...
Well i have been thinking of something similary for the last five years.
Carbon/kevlar/glass or ....

It is probably doable without a autoclave.

I think you could do it in glass (mini marcos, Midas and GTM rossa-libra) for ex.

The backside of doing it in the “backyard”, is the health issues.
Epoxi and the other chemicals are not good for you (some say no problem other do).
You could always dress appropriate for the task. The hard bit would be the rest of the family, getting bikes or a tool and by mistake touch something.
You have to be very carefully not to bring anything in to the house.
I have read some of the Hazard instruction on prepegs and it’s noting you want to take to bed….

nothing is impossible......

There have been plenty of responses to this thread and if you have a quick glance at the history of "alternative chassis materials" threads, they all show robust levels of discussion.

Fact is, tubular steel, either RHS or round is a known quantity. This goes for constructors as well as the authorities.

CF is certainly the current "wonder material" the same as aluminium was in the 50's and 60's . The last robust thread on chassis materials was the Aluminium chassis thread or maybe the latest aluminium thread that I saw.

The main thrust of the last ally thread was, "design for the material". Several examples were served up to indicate that a Seven chassis would require a significant re-design for a change to aluminium.

With CF, there are a bunch of relevant factors. Primarily, if this is to be a road registered vehicle, the beak must be convinced that the chassis is safe. There has been a significant post on this issue from Delinquent.

Another factor is design. CF has it's own set of requirements, all of which you'll have to become familiar with if you want to construct anything with it.

As far as impact resistance is concerned, I'm reminded of a statement made by a chap I know who makes million dollar masts for racing yachts (I kid you not) his take on CF is: "Carbon Fibre is incredibly strong for it's weight but when it fails, it snaps like a carrot" I often think about this when riding my CF framed bike.

Finally. Building anything in CF can never be deemed "locost". The last time I checked, there was a worldwide shortage of CF cloth especially in the 2K to 4K weights. Our friend Dennis (DP-1) appears to have relatively deep pockets but to he rest of us I think the prospect of buying enough square metres of CF to make a car chassis might cause some distress.

As Jo C says "nothing is impossible" I'd add, "given enough time and money"

[Edited on 9/4/08 by Benonymous]

Benonymous, I was looking to step into this one, but almost word for word you have voiced my feelings.

Regarding Dennis (DP1) I have a lot of respect and admiration for what he has achieved so far, but I'm pretty sure that his progress so far with the CF tub is just the attractive Solidworks model shown on his site...I'm not saying it won't be a perfect tub, just that it isn't one yet and that to look at the model and say something like "see look, it can be done" is a bit of stretch to say the least.....even more so for locost-deep pockets.

I'm all for pushing envelopes....giving it a go etc......but without some realism there were will a lot of empty piggie banks and unfinished projects.

So please by all means you CF tubbers prove me wrong....I know some will and hope you do, but for most of us will do well to heed the words of the old design engineers motto....

When in doubt, make it stout, out of something you know about....

I would add to the above excellent Benonymous post:

You must consider what would the benefits might be over a steel frame-

Lighter weight - how much actually?

Stiffer - are you going to spend mega bucks on proper multiway adjustable coilovers to take advantage of this stiffness?

Bling - how much is this worth to you?

To me it seems a hell of an increase in cost and hassle factor for any (maybe slight) improvement over a steel frame

Cheers

Fred W B

[Edited on 9/4/08 by Fred W B]

Well, I intend to build glass-fibre sandwich monocoque chassis, and my guess is that it will be lightweight (the part shown should weigh less than 25kg) and cheap. Simple wet lay-up, no autoclaves and no nonsense (but I guess parts will have to be vacuum-bagged for post-cure)



The drawing doesn't show 4 Al bulkheads that will be glued to it to increase torsional stiffness, mount engine & suspension, and protect the driver a bit...

As for strength- I've seen a specification for aircraft fuselage with similar layup, the difference beeing mine is (IIRC) 2x as strong and 8x stiffer (and that's without tophat/box sections I used for siffening).

thanks for all the tips guys. its particularly interesting to read about the negative aspects of CFRP, thanks.

Wolfr, excellent work my friend! I salute you. have you designed the rest of you car, cos id love to see your design progression. amazing work. I will suggest, if u didn't think of it yourself, fill those openings with expandable foam for extra impact absorbtion. if u did think of that, gr8 design.

I think, and was always rooting for, the GRP sandwich is a good direction to go with for featherweight chassis, not forgetting to add in stiffness where needed, as Wolfr also suggested.

Its gr8 to see where this discussion progressed to. thanks again guys.

I've watched this thread with interest.

'I've made one in the past'??? Well, more than a few, and the 'past' is present and ongoing. It's part of my work.

Carbon is not a wonder fibre, but must be treated with due respect. Yes, it does crunch like a carrot when it goes. To use carbon, and other hitec fibres, you must have a full knowledge of load paths, and resin properties. All of those snapped yacht masts are due to simple poor engineering, and complete lack of it in most cases.

Wet layup carbon composites are little better than a good hispec glass item. To get the full benefit of carbon, or any of the modern fibres, then an autoclave to cure the layup is imperative. If you haven't got access to a clave, then forget carbon.

In the pretty racecar tubs you see, with the nice weave showing, the real work is done by unidirectional fibres, hidden underneath.

If contemplationg glass, then I sincerely hope no CSM is involved. Otherwise, you just waste a lot of time and effort. Use as much unidirectional fibre as possible, and orient it suitably. Put it outside of the best core material you can afford. NO foam that isn't PVC. Again, waste of time. The two skins DO move against each other, and will quickly separate from a poor core choice.

I've said too much, but enough for you to be dangerous!

Cheers,
Syd.

There has been an article in the last two Complete Kitcar magazines about a guy who built two (one for him, one for a mate) carbon fibre cars (kind of GTM Libra but more wedgy shaped). Took him 15 years IIRC and he's now got an autoclave in his garage and a big pile of scrap panels. Learning how to take advantage a new (to you) material takes a lot of time, money and hard earned experience.

Mr Bridge has been doing it for a lot of years - and if I really wanted to do it I'd get a quote from him. Unlikely to be cheap, but still much much cheaper than doing it yourself from a standing start.

A steel spaceframe will be 90% as good, cost a couple of percent as much, and done in a couple of months. SVA man will just look at the welds and make sure it's not horribly under-triangulated.

Finally don't underestimate how bad for your health epoxy resins can be.

Have you looked at how the GTM libra is made?...

Thata a GRP monocoque with steel front and rear subframes.,.....

Doesnt look overly complex!

I guess the issue is knowing just how strong the GRP is....

I currently drive a GRP chassied car

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Originally posted by tegwin
Have you looked at how the GTM libra is made?...

Thata a GRP monocoque with steel front and rear subframes.,.....

Doesnt look overly complex!

I guess the issue is knowing just how strong the GRP is....

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so true delinquent. I have read a bit on grp and cfrp chassis. the strength is in the layout, the specified plastics, and sometimes added structural support.

Heres a few pics of the GTM LIBRA, interesting tub design. lots of box sections and corners for extra support:

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I use carbon a great deal in my RC heli's - making a blade with a weave in one direction over another can be the difference between a sweet flying machine or something that struggles to get off the ground and then is a mare to control with blades bending left right and centre.

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Try 65:25:5:5 for your fibre orientation ratio (0,90,+45,-45)

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Delinquent - 10/4/08 at 09:30 PM

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Originally posted by twybrow

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I use carbon a great deal in my RC heli's - making a blade with a weave in one direction over another can be the difference between a sweet flying machine or something that struggles to get off the ground and then is a mare to control with blades bending left right and centre.

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Try 65:25:5:5 for your fibre orientation ratio (0,90,+45,-45)

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co-incidentally, that's exactly what I ended up with as my preferred layup

It's also what I intended to use on the majority of my car tub, as it's what I've had most success with - then was going to try and work out what to do with load paths in the more highly stressed area's, such as suspension mounts etc. Haven't quite worked out what I'm going to do there yet (read: got fed up through sleep deprivation and will re-address once new baby has started to sleep for more than an hour each night...)

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rpmagazine - 10/4/08 at 09:47 PM

For a wet layup the devil is in the deatil in some respects. If you use a polyester resin then you are asking for trouble and frankly need a good slapping...particularly if you use carbon/kevlar.
Wet layup is unlikely to meet the same performance standards of prepeg or zpreg, however the simple solution is that you use more.
You can always vacuum bag the wet layup too.
An autoclave is not required, work with the resin supplier and get a low/mod temp cure vynalester/epoxy and you can successfully cure it in a paint oven over night. It will cure without the heat, but the post cure can add an extra 10-15% and more crucially make the resin less susceptible to hot days.
This last bit is important...the resin WILL lose performance when it gets hot, vynalester is perhaps better than most wet layup epoxies...but check with the resin supplier...they will know what is best.
FWIW my Rochdale Olympic is 4500lb/ft torsionally

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nitram38 - 10/4/08 at 09:49 PM

Monocoque carbon or fibreglass structures are rich man's toys. Come to that even Aluminium monocoques have a limited life span.
Good old steel spaceframe chassis will last longer and be easier to repair.
That is why most DIY car builders go down this route.
If you take aircraft as an example, their airframes are the biggest reason for limited life span and their eventual scrapping.
Nothing lasts forever but you should get more life and easier repairs with steel.

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Puk - 11/4/08 at 06:43 AM

Nitram - I agree that most people build steel space frames because they are easier to design & fabricate (relative to any type of monocoque or Elise type twin spar). But I don't agree that there is any engineering consideration for it to stay like that. Whilst there are plenty of steel truss plans to follow or examples to copy from it is pretty hard for any one but a trained engineer to do anything else.

In the last 10-15 years the other materials have come to the for in the in formula where they are not prohibited, or put it another way, steel trusses are not competitive when alternatives are permitted. F3, which doesn't have F1 budgets by any means, went CF years ago, hill climb is dominated by CF or al alloy chassis. Elise, Jag XK and XJ, Audi, Renault Spider all have adopted structural al chassis. And bear in mind there are not cars with a "drive before by dates" or Maclaren price tags. But to not do a steel truss requires the determination to learn how to design it your self (i.e. more reading and more prototyping) and I guess that most folk would be happier driving!

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iank - 11/4/08 at 08:20 AM

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Elise, Jag XK and XJ, Audi, Renault Spider all have adopted structural al chassis.

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One of the main reasons spaceframes, and indeed almost all separate chassis, have been phased out in production cars is because of cost. They are labour intensive to make as they don't lend themselves to automated manufacture. Any people involved in the process need to be skilled welders so cost more than unskilled people.

On your points regarding racing cars moving to CF and monocoques. Yes they have, for a lot of reasons, not all technical (I'm always amazed how much herd instinct and fashion have to do with what is used), but no-one here has said CF and monocoques aren't better than spaceframe. Just they are harder to design and make and any additional performance you can theoretically get just isn't worth the money and time.

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Delinquent - 11/4/08 at 08:49 AM

There is another reason to use a composite chassis - economic use of space.

When I started my design, the first thing I did was draw out a spaceframe chassis. Then I started trying to fit things in and around it. Every approach I took resulted in compromises due to large bits of steel sticking out where they weren't ideal, but moving the bits of steel resulted in a less than ideal chassis.

Then when you consider that to create a decent ergonomic environment inside, you need to skin all this spaceframe... if it's a complex shape (which as a three seater mine is) you end up choosing a composite... if you are going to the trouble of making moulds for the composite, why bother with the steel at all? Just make the composites structural.

One route I am considering at the moment to overcome the SVA issues is a mix of the two - a very simple steel roll cage to pick up the most stressed points, with a sort of semi-structural composite tub around it.

Of course that brings up more issues in itself. Ho hum!

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smart51 - 11/4/08 at 09:05 AM

I built a recumbent tricycle out of carbon fibre a few years ago. It is no more tricky to wet lay carbon than to do GRP. West Epoxy takes about 8 hours to cure at room temperature. Every 10° C halves the cure time, so 60°C cures in about 30 minutes, 70°C in 15. I used a domestic oven on its lowest setting. You're limited to the size of parts you can cure though. I'm told a heat gun and a poly tunnel are good.

I found when destruction testing early prototypes that CFRP is much tougher than GRP and stands up to knocks better, even in thinner section. when you stress it too much, it just snaps. I didn't use vacuum bagging either. I was careful when laying up, rolling the laminate very thoroughly to take out excess resin and air bubbles.

That was before the A380 and the doubling of price of carbon cloth. I wouldn't do it now.

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Delinquent - 11/4/08 at 09:11 AM

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Originally posted by smart51
West Epoxy takes about 8 hours to cure at room temperature. Every 10° C halves the cure time, so 60°C cures in about 30 minutes, 70°C in 15. I used a domestic oven on its lowest setting. You're limited to the size of parts you can cure though. I'm told a heat gun and a poly tunnel are good.

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Friend of my father used to make masts for racing yatchs, they used to make thick poly tents over them and stick an industrial heater under it with a thermostat!

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Puk - 11/4/08 at 09:13 AM

Iank, I don't think that we disagree, particularly your point about the importance of herd instinct. My mail was to pick up on Nitram's point:

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Originally posted by nitram38
Monocoque carbon or fibreglass structures are rich man's toys. Come to that even Aluminium monocoques have a limited life span.
Good old steel spaceframe chassis will last longer and be easier to repair.
That is why most DIY car builders go down this route.

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I agree that a steel space frame is easier to get right for most of us (they're tried and tested, loads of examples to copy from). But the disadvantages listed for the alternatives are look more like opinions than facts.

So I don't agree that is an argument to reject alternatives. Only that alternatives do require more effort / stubbornness / research to get right.

The CF mono alternative to the space frame isn't theoretically better - its been proven on the track - take F3 - there is no rule compelling people to stop using space frames. But if they don't have a chance of winning they may as well pack up and go home - hence the move to CF.

But personally I'm not going the CF route, I don't feel comfortable about being able to design it right, or build it in a garage. Al composite panels and structural adhesive on the other hand . . .

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nitram38 - 11/4/08 at 09:20 AM

Puk, just because something can be done, doesn't mean it should.
Cost and longevity is going to stop most people from going this route.
In my ideal world, I too would have a CF car, but my finances, facilities and my time limit this.
If you already have access to these materials and facilities, then go for it.
There are a lot of builders that don't even finish a steel car, so getting them all excited about a project that is more difficult to create is what I am talking about.
Most people building cars on here are going to use them on un-even roads, race cars are generally on smooth tarmac circuits.
Also most racers will buy their cars, not build them.
They leave the building to people with the facilities and experience.
As I said, Rich Man's Toys.

[Edited on 11/4/2008 by nitram38]

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Puk - 11/4/08 at 09:31 AM

Fair point. I'm not saying go ahead abandon steel, but I am saying to abandon steel is a hard thing - so be aware of what you're getting into. I disagree that steel alternatives inherently have short life spans or are more difficult to fabricate. CF is harder to fabricate, but al composite is not.

This chassis cost half the price of a FF space frame, because although the components are more expensive you spend a day bolting them together rather than a week welding steel tubes.


Linky to picture

Its tougher in a crash too.

[Edited on 11/4/08 by Puk] Bloody hell adding pictures is an art! Lets go back to fax!

[Edited on 11/4/08 by Puk]

Formula Lotus Chassis

[Edited on 14/4/08 by Puk]

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Delinquent - 11/4/08 at 09:42 AM

quote:

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Originally posted by nitram38
Puk, just because something can be done, doesn't mean it should.
Cost and longevity is going to stop most people from going this route.
In my ideal world, I too would have a CF car, but my finances, facilities and my time limit this.
If you already have access to these materials and facilities, then go for it.
There are a lot of builders that don't even finish a steel car, so getting them all excited about a project that is more difficult to create is what I am talking about.
Most people building cars on here are going to use them on un-even roads, race cars are generally on smooth tarmac circuits.
Also most racers will buy their cars, not build them.
They leave the building to people with the facilities and experience.
As I said, Rich Man's Toys.

[Edited on 11/4/2008 by nitram38]

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I'm most definitely not rich by even the average persons standards - not even well off. About the only thing that looking at a composite monocoque has cost me so far is time and reading researching it - which although incredibly frustrating at times I've enjoyed for the most part, and have learned skills that can be used elsewhere in the build.

Will it cost more than a steel spaceframe to build? of course it will, but for me building this car is about pushing my boundaries, learning new skills and achieving something I've not done before. If I welded together a load of steel tubes and dropped a body over it I'll have achieved nothing new, just spent my time doing "another" project for the sake of another project.

It may well end up that way if the extension costs keep spiraling as they are, but it's something to aim for...

[Edited on 11/4/08 by Delinquent]

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Alan B - 11/4/08 at 12:07 PM

quote:

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Originally posted by nitram38
............. There are a lot of builders that don't even finish a steel car, so getting them all excited about a project that is more difficult to create is what I am talking about.........

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Excellent point.

Those with the knowledge, determination and cash will do it, and do it well I'm sure. I admire and applaud you for that.

It's the new guys reading this thread and thinking "Oh, I might have a go at that" that I'd really advise to stick with simple, proven and cheap.....and ultimately way more achievable.

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Doug68 - 11/4/08 at 12:27 PM

Some observations:

1. A Porsche 917 frame weighs 42kg the Bentley LMP from 2003 weighs ~70Kg which do you think is better and why?

2. CF and other processes "novel" to the home builder won't be widely accepted until they are widely understood. One day someone will write "How to build a Carbon Fibre Hypercar for less than 5000 quid" then all of a sudden 100,00 people will be "experts" on the subject (Just like we all are with steel frames ), but until then...

3. These processes and techniques are not widely understood today (least of all by me) hence all the "Burn the Witch" posts that are generated every time this subject comes up.

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chunkytfg - 14/4/08 at 03:16 PM

quote:

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Originally posted by Gakes
Like I said before, this must be the best site ever. Anything is possible and this forum has all the right members

I thought it was possible, not just wetting myself How does the vacuum bag work??

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Not sure if you have had an answer to this yet as i havnt read the whole thread but have a look at this for insiration and help

http://www.bayarearidersforum.com/forums/showthread.php?t=145975&pp=15

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Benonymous - 16/4/08 at 11:50 AM

Just read the whole thread on BARF. Very interesting. However, let's not forget that a motorcycle fuel tank is not a structural part as such. I admit it has a critical role and has to be strong enough not to split and spew fuel everywhere in the event of an accident but it's not carrying any load.

Another very interesting point to be learned from the above thread (link) is the actual amount of work involved in making a part. The effort required to get a nice shiny (out of the mold) CF part is pretty high even for a relatively small part like this.

Finally, the builder remarked several times on the availability of 'certified' CF cloth. The last time I checked, there was little in the 2K or 4K area available thanks to the abundance of demand (aerospace) and the lack of CF manufacturing facilities. For a chassis, you'd have to use certified cloth unless you just want the cosmetic look rather than the strength. This kind of shortage drives up prices.

It's one thing to want to do a CF chassis but another to commit the time and money to achieve it. At the present time it looks like its a project for the well heeled, not the Locost builder.

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Ferg - 26/4/08 at 05:07 PM

quote:

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Originally posted by tegwin
Have you looked at how the GTM libra is made?...

That's a GRP monocoque with steel front and rear subframes.,.....

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Actually it's a GRP monococque with a frame that holds the engine. The suspension is simply bolted through the GRP with a small plate on the inside. It has no additional strength barring two 2" square steel plates in the 'B' pillar for the upper seat-belt mounting. No coremat, no laminated in metal etc.

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robroy - 16/5/08 at 05:12 PM

Hello everyone. Great thread on a great forum! I salute you all.
I've been thinking about my next project, a single seater road/track car and its chassis construction. I'm hoping it'll be 500kg with driver and fuel and will have maybe 100bhp so we're not talking massive speed here.
I've been looking into the cheap side of composite construction and there hasn't been much information on the net and I still have many thoughts on the subject. I have found this interesting old article though:
http://www.rqriley.com/frp-foam.htm

Here is a sketch of my project:


One of the advantages over spaceframe I see is that I can achieve a finished surface on the outside of the tub without creating bodywork for the mid section. Some time and effort saved.

I have incorporated 'gentle' curves into the panels - will this substantially reduce the strength?

I guess I could always combine the two, and build a spaceframe chassis and fit a lightweight core between the tubing around the tub before glassing around it for extra strength. Heavier but should have impressive rigidity and crash protection, and can again use the outside of the tub as a finished surface.

Also, I notice that no one has mentioned end grain balsa as a core, although much used by airplane or boat builders where it can achieve impressive rigidity in half inch panels. Anyone have any concerns about using this core?

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Puk - 16/5/08 at 05:21 PM

I think that Elden built some formula cars in the 70s using end grain balsa core with al skins. I worked there one summer way after their hey day and the boss had a desk made out of the stuff. Any one know anything more about them?

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Wolf HR - 17/5/08 at 08:57 PM

Puk, it was called Mallite and was IIRC pioneered by McLaren in Formula 1 in late sixties...

I imagine it would be suitable for flat surfaces or with very little curvature, whereas foam core would be more suitable for cars because it allows compond curves (and the benefit of using lighter but thicker core would be stiffer structure)...

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Puk - 18/5/08 at 05:32 AM

Google threw up:

"Formula 1, works team Mallite monocoques intended for Ford Indy V8 power, also used Serenissima V8"



So can be done. As with all these discussions about alternative chassis materials - if you want to go that route you need to know how to use the materials. Which doesn't necessarily imply a degree in engineering, just a good head for reading. Allan Staniforth writes about a single seater hill climb car that was built by a school teacher from carbon in the late 80's IIRC. The chap modeled it on an F1 Jordan and the chassis is still being raced. A good starting point would be to ferret out the design guides that Hexcel used to provide some for using the composite panels that they used to supply.

wooden linky

Cheers,
Puk

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rpmagazine - 18/5/08 at 07:16 AM

have a look at www.ayrescom.com

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Ians - 18/5/08 at 02:38 PM

I am the teacher mentioned in PUK's last post, I can only add that for the last 15 years composite construction has been my chosen method of build, it does require a lot more design preparation prior to starting (any changes or design flaws can often render produced moulds ineffective, it will always be easier to cut and move tubes and modify a space frame). There are obviously many more pitfalls and avenues of failure when dealing with monocoque constructions and priorities must lay in defining load paths. I personally feel whilst it may not have an advantage over a spaceframe for the amateur or first time builders it offers a challenge that some may find worth the effort. Ians.

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Puk - 18/5/08 at 03:15 PM

Ians - nice to "meet you" thank goodness I wasn't disrespectful in my post.

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Delinquent - 18/5/08 at 04:29 PM

quote:

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Originally posted by Ians
I personally feel whilst it may not have an advantage over a spaceframe for the amateur or first time builders it offers a challenge that some may find worth the effort. Ians.

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That's the key to me. Steel tubes are simplicity themselves and cannot be faulted for their ability to do the job - but it's just not that challenging to make a decent chassis out of them.

(my emphasis)

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Dick Bear - 19/5/08 at 04:01 AM

Hey Delinquent if you keep chipping away at this you will eventually assemble all the data and resources necessary to build that monocoque of your dream.

I, for one, am looking forward to your success and am waiting patiently for the build to begin.

Good luck!

Dick Bear

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Gakes - 19/5/08 at 06:38 AM

great posts guys, you've just made me realize to look to aerospace and aircraft technologies

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Delinquent - 19/5/08 at 06:53 AM

quote:

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Originally posted by Dick Bear
Hey Delinquent if you keep chipping away at this you will eventually assemble all the data and resources necessary to build that monocoque of your dream.

I, for one, am looking forward to your success and am waiting patiently for the build to begin.

Good luck!

Dick Bear

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Cheers mate

Got plenty of time for the design and research stages at the moment - I was supposed to have started the build about 6 months ago but have still got problems with the bloomin workshop going up!!! May have to re-apply for planning yet AGAIN

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