SeanStone
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| posted on 18/1/11 at 09:25 PM |
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Carbon wishbones
Can/should it be done?
One of the things I would like to be able to do to but I don't know whether they'd be too fargile
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scootz
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| posted on 18/1/11 at 09:28 PM |
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It CAN and SHOULD be done (well, the F1 cars have been doing it for aeons!  ).
Let us know how you get on!
It's Evolution Baby!
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SeanStone
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| posted on 18/1/11 at 09:30 PM |
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Is there any geometry available for the IRS locost chassis wishbones? While I'm still at uni it might be a useful to give it a crack there while
I can
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HowardB
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| posted on 18/1/11 at 09:33 PM |
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where are you at Uni, there was a huge amount of data on composite springs when I was at Uni (twen-cough-ty years ago!)
I was at Plymouth
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SeanStone
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| posted on 18/1/11 at 09:34 PM |
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I'm at oxford brookes. And I used to go to Brooklands College in Weybridge who I know have an autoclave big enough for wishbones that I could
use!
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plentywahalla
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| posted on 18/1/11 at 09:39 PM |
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It can be, but it must be done properly which is very different from knocking up the odd wheel arch or dash panel.
The method we have used for making carbon keel blades for racing yachts is they are a solid foil profile. This is laid up in a mould with one side
profile and laid up using progressively tapered layers of woven unidirectional carbon cloth and epoxy, and then reducing tapers until the otherside
profile is achieved. The whole is then skinned with bi-axial cloth. The finished item is then post-cured in an autoclave.
You will also need to spray lacquer it as epoxy is not UV stable and will degrade.
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britishtrident
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| posted on 18/1/11 at 09:54 PM |
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F1 "carbon fibre" wishbones break with monotonous regularity they are designed to take loads only in the designed direction.
Carbon fibre is a very stiff but brittle material as a result most if not all of the engineering structures we call carbon fibre use a
high percentage of Kevlar and even E Glass fibres in the lamination.
As Rolls-Royce found with the failures of original Hyfill Carbon fibre compressor blades Designing in high performance carbon fibre composite
materials is a 300 times more demanding than designing in steel and 100 times more difficult than designing in light aluminium or magnesium alloys.
in short unless the design is checked with a specialist laminate FEM program by a FEM practitioner specialising in composite materials then it is
very likely not to be up to job and to fracture.
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snapper
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| posted on 18/1/11 at 10:02 PM |
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There was a collaboration between an aircraft company and a university which did wishbones on a Caterham uni project about 2 years ago, they used ally
ends with carbon tubes. Looked fantastic.
I eat to survive
I drink to forget
I breath to pi55 my ex wife off (and now my ex partner)
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plentywahalla
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| posted on 18/1/11 at 10:23 PM |
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Don't mix aluminium with carbon fibre ... you'll get horrible electrolytic issues. All metal fittings we used were stainless steel.
I'd agree with Britishtrident, Unless you are in a position to use non-destructive testing of the component I wouldn't do it.
I forgot to add that each lay-up needs to be vacuum bagged to ensure the total elimination of any voids and correct saturation of resin to cloth.
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James
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 posted on 18/1/11 at 10:23 PM |
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Without some serious testing data I wouldn't even attempt it.
F1 wishbones are lifed to a very short duration.
If Caterham with all the experience, R&D budget and facilities haven't done it (and think of all the muppets who'd tick that option
box) then I just don't think it's a go-er.
I know it's nice to save unsprung weight but I don't think this is something the DIYer can sensibly attempt.
Sorry to be negative!
Cheers,
James
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"The fight is won or lost far away from witnesses, behind the lines, in the gym and out there on the road, long before I dance under those lights."
- Muhammad Ali
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SeanStone
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| posted on 18/1/11 at 10:26 PM |
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A swift conclusion has been struck it seems!
So what's the next-best, viable option for making light wishbones?
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britishtrident
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| posted on 18/1/11 at 10:32 PM |
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Fabricated Steel or cast in light alloy
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James
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| posted on 18/1/11 at 11:15 PM |
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quote:
Originally posted by SeanStone
A swift conclusion has been struck it seems!
So what's the next-best, viable option for making light wishbones?
I really don't know if there is a sensible way. I suppose the bush tubes could be of stuff a bit thinner wall if they were seamless tube. The
wishbones really aren't that heavy relative to other bits of the car.
There are other more worthwhile places to save weight.... build the chassis to the Cymtrics plans, use 13" wheels, alloy uprights and brakes,
keep the loom as short as possible, lightweight diff, minimise clocks, thin bodywork, GRP seats, minimise bolt sizes and lengths. But probably the
single cheapest way to lose weight is to.... lose weight! Going on a diet will be the cheapest and probably best way!
At the end of the day with a Xflow or Pinto these cars are pretty damn fast and fast enough for most people's driving skill... you are putting a
S2000 engine in yours!
Cheers,
James
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"The fight is won or lost far away from witnesses, behind the lines, in the gym and out there on the road, long before I dance under those lights."
- Muhammad Ali
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balidey
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| posted on 18/1/11 at 11:25 PM |
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quote:
Originally posted by SeanStone
So what's the next-best, viable option for making light wishbones?
Firstly, who says that the current tried and tested wishbones are overly heavy? Do you honestly need lighter weight bones?
Secondly, heres some pics of a wishbone I have fab'ed up from thin gauge steel, formed over an alloy pattern and seem welded with bosses welded
in. They are 'light' but are from an F1 car so will probably have been designed to take higher loads than a road car. So could possibly be
made lighter for road use. Or should they infact be made heavier for road use? Last thing you want to do is go light weight and regret it mid corner
because you saved an ounce.
Dutch bears have terrible skin due to their clogged paws
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orton1966
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| posted on 19/1/11 at 06:50 AM |
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Carbon Tubes + Ends
I’m not discounting all of the above concerns but personally I don’t see the problem. If you can make a mountain bike frame in composite that has a
reliable service life a wishbone is not beyond the bounds of someone who takes a logical and careful approach to its design/construction.
Simplest way would be with tubes with end fixings bonded (read glued) in. Tubes can be purchased from several manufacturers to almost any spec you
specify. Elliptical and aerofoil sections are also easily available. End fixings could be simply machined, with due regard for bonding/reducing stress
raisers from an appropriate alloy. Apart from the sourcing issues and machining of ends this construction process is no harder than making a
conventional set of bones. This was the first technique used to make commercial bike frames, probably 20+years ago!
The trick with using exotic materials is, unless you are racing or can afford massive testing, is don’t be tempted to go too light. Back to the bike
example; very good steel road frame about 1.2kg, in alloy 1.1kg, in Carbon just sub 1kg. If you want carbon wishbones fro the cool factor or to just
show you can, sensibly design and make them the same weight as current mild steel ones, they will be strong!
As a side I’m thinking of using a composite tube for the pushrod element of my inboard suspension, very easy to figure the load path and easy to over
engineer, not such a leap of faith as the wishbones
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Ivan
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| posted on 19/1/11 at 07:15 AM |
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Only half joking - if you want it for looks then wrap your steel bones with carbon style wrap.
The above notwithstanding - as others have said - if you want to save unsprung weight - or in fact any weight, there are much more effective ways of
doing it with much less risk of failure or design effort than concentrating on the wishbones.
I'm sure that an all out effort with Very careful material, engine, wheel and tyre selection and FEA could fairly easily get the all out weight
of a se7en down to around 350 kg.
A live axle with aluminium diff housing such as those from the rear wheel drive Alfa's would be an early choice and would most probably be a
significant contributor to weight saving especially if you fitted lighter weight tubes.
Then there's Cymtrixe's chassis mods, lighter uprights and hubs and brakes, no windscreen, etc etc.
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balidey
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| posted on 19/1/11 at 07:53 AM |
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Or do a big poo before every journey as that weight saving will be about the same as carbon vs steel wishbones.
Dutch bears have terrible skin due to their clogged paws
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SeanStone
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| posted on 19/1/11 at 08:46 AM |
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so what are these chassis mods you're talking about? i'd definately like to try and get lighter hubs and brakes yes, maybe the hubs could
be designed from a folded steel arrangement. the FEA wouldn't be too complex on that.
this is all just think out loud really. the car is on pause while i'm at uni but i think as i'm here there must be a way of utilising the
facilities. i've already designed and built a billet dry sump pan at uni, now i'm about to start designing the pump and swirl pot to go
with it.
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balidey
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| posted on 19/1/11 at 09:39 AM |
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quote:
Originally posted by SeanStone
maybe the hubs could be designed from a folded steel arrangement. the FEA wouldn't be too complex on that.
Actually it would. Well, actually 'doing' the FEA is a piece of cake its just a few button clicks, but using FEA correctly is a very
specialised skill. I can 'do FEA' but I know that it must never be used without tests to back up the results. Its a tool to help testing
or perhaps guide your design in certain areas, ie if you have 20 designs to test then you can use FEA to whittle down the numbers of iterations to
test.
I am a mechanical design engineer with a good understanding of FEA. But would I feel comfortable using FEA to design a hub on my own car? No. 100%
not. And that is where the biggest problem with FEA lies, because its easy to use most users think they are getting good information out, but with
most things if you are not confident and experienced with FEA then there is no point doing it.
And this is not meant as a criticism on you or your knowledge, its not. Its just that I have seen on too many forums people saying they can do some
FEA on an item. Unless its their full time job then I personally would never recomend it. A good case in point is my work commissioned an engineering
company (very well respected, does a lot of work for other top level car manufacturers). They took my model, applied FEA to it, but they made a few
mistakes in how they did the FEA. We built a test vehicle (as its normal practice after FEA) and the design collapsed. That is from an experienced
company.
So have a play with the FEA, but please don't rely on it for a very critical part.
Dutch bears have terrible skin due to their clogged paws
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Ivan
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| posted on 19/1/11 at 12:06 PM |
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quote:
Originally posted by SeanStone
so what are these chassis mods you're talking about? i'd definately like to try and get lighter hubs and brakes yes, maybe the hubs could
be designed from a folded steel arrangement. the FEA wouldn't be too complex on that.
Have a look here
http://locost7.info/mirror/chassis.php
and download relevant documents.
As said before by others use your discretion in applying them.
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eddie99
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| posted on 19/1/11 at 12:17 PM |
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Pfftt i disagree with some of the above comments, if you want to learn into Carbon fibre, then go for it, do your research, have a few attempts. Not
sure how helpful Brookes are, but Cov are fairly helpful. Worst comes to worst, you end up going back to using normal wishbones and have something
cool to put on your wall having learnt a lot 
I guess its just another way of looking at it...
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Twitter: @Elitemotoreng
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iank
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| posted on 19/1/11 at 07:00 PM |
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quote:
Originally posted by eddie99
Pfftt i disagree with some of the above comments, if you want to learn into Carbon fibre, then go for it, do your research, have a few attempts. Not
sure how helpful Brookes are, but Cov are fairly helpful. Worst comes to worst, you end up going back to using normal wishbones and have something
cool to put on your wall having learnt a lot
I guess its just another way of looking at it...
Worst comes to the worst and you'll take out a line of kids waiting for the school bus before putting yourself in a wheelchair and pooping into
a bag for the rest of your life.
Radically new designs aren't for the road until serious testing has been done IMO.
Titanium might be worth a look, there are companies making mini suspension components out of the stuff, whether it's a suitable material and
what the best design would be are worth a research project. But again move with caution until sure it's safe.
--
Never argue with an idiot. They drag you down to their level, then beat you with experience.
Anonymous
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eddie99
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| posted on 19/1/11 at 07:14 PM |
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Thats true, but in my opinion, if sean is doing this to learn and does proper testing, he's not going to be stupid enough to put them on his car
if he knows they are not safe without doing proper testing.
Theres a lot more bodge jobs that have been done on here that can lead to such a dramatic disaster more than this.
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Twitter: @Elitemotoreng
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RK
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| posted on 19/1/11 at 07:46 PM |
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Since there is zero chance that I would be around your neighbourhood whilst you are testing, I say go for it!
PS there is a reason why only cross-country, and road bikes, have gone the CF route for main tubes. Downhill bikes would shatter like glass and stab
the rider senseless in the event of the inevitable failure. Things break regularly on DH bikes due to the forces. I don't miss the falls one
single bit, and I certainly don't miss the A and E wards I saw with regularity.
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plentywahalla
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| posted on 19/1/11 at 08:10 PM |
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I have been toying with the idea of making some sand cast aluminum wishbones in LM25 then machined, polished and anodised. There is a local foundry
that I have worked with in the past and have an excellent reputation for high quality castings. Many years ago I had them cast some prototype alloy
wheels from a pattern that I made and they machined up perfectly. The wheels were for an off-road racing kart but that is surely a more demanding
precision application than making wishbones.
The advantage is that you only have to make one loose pattern in wood for each wishbone type. Its going to be lighter than fabricated steel. And you
can make some very sexy aerofoil profiles.
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