). Let us know how you get on!
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
It CAN and SHOULD be done (well, the F1 cars have been doing it for aeons! ).
Let us know how you get on!
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
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
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!
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.
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.
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.
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.
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
A swift conclusion has been struck it seems!
So what's the next-best, viable option for making light wishbones?
Fabricated Steel or cast in light alloy
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?
quote:
Originally posted by SeanStone
So what's the next-best, viable option for making light wishbones?
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
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.
Or do a big poo before every journey as that weight saving will be about the same as carbon vs steel wishbones.
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.
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.
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.
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...
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...
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.
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.
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.
can they be made out off billet ally???
IRCC fatique was attention point when engineering and constructing in billet ally. You could use airspec 6061 alloy for the uprights.
Formula Students have extensive analysis on their suspension and their reports are widely avaible on the web. Those crazy students aren't afraid
to engineer in exotic materials
You could use filament carbon tubes, you then only have to figure a clever joining system
PS: Why is this in the bodywork section?
[Edited on 19/1/11 by ettore bugatti]
Informational link:
http://fsae.com/eve/forums/a/tpc/f/125607348/m/15110476641/p/1
This thread reminds me of the many "why not build the chassis out of aluminium" threads.
If you want to save weight on a clubman style car there are many, many ways to do it without resorting to experimental parts in critical areas of the
vehicle. The running gear is one area that I would never attempt to use exotic untested materials in.
Sure, F1 teams use CF for everything but an F1 car is unlikely to have a wheel drop into a pothole on a B road or clip a concrete kerb. I know F1
cars run over ripple strips on tracks and so forth but they are not putting massive instantaneous loads on the suspension when they do. I read an
article once that pointed out "Carbon fibre has a very high strength to weight ratio but when it fails, it snaps like a carrot!"
That's your wishbone he's talking about.
Metals tend to fail more progressively and so you'll avoid that look of a crashing F1 car with the wheels flying off in four different
directions.
You'll never regret over engineering the running gear on your car but you'd definitely regret under engineering 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."
I've a 6" travel single-piv frame with a carbon swingarm, still going strong after nearly a decade of use
But I wouldn't use carbon on the wishbones for the two reasons I see noted above. 1 - when they fail they fail spectacularly - there'd be no
pullin to the side of the road with a screech - it'd be snap, scrap, stop at best. 2 - the weight saving is minimal for the effort and concern
I'd have over the final result. And I'm one of those crazy student types making stuff in exotic materials. We've billet uprights,
carbon driveshafts, custom-housed minimalist diff, but our arms are still good old steel tubing
If its for a track only car then I'd say go for it!.
If its for a road car, I'd say save the sprung weight elsewhere - 13" wheels, thinnest/lightest brake disks etc
Regards
Hugh
quote:
Originally posted by hughpinder
I'd say save the sprung weight elsewhere - 13" wheels, thinnest/lightest brake disks etc
I would say using carbo fibre for wishbones to save a knats knacker in weight wouldn't be worth the expense, if they were stroner enough for road
use in the first place!!!
Fit a bike engine, 13" wheels and don't eat so many pies...........
Think about this military combat helmets are made of Kevlar (they likely also contain glass fibres in the lamina) not carbon fibre.
quote:
Originally posted by hootsno1
can they be made out off billet ally???
Just to add another voice to this- No. Just no.
Can i go back and resuggest wrapping steel wishbones with fake carbon. It will add a couple of grams and will look the business (if thats your sort of thing) until it gets chipped.
What about making the wishbones out of T45 alloy?
They'll be substantially lighter than the steel ones, then you always have the option of wrapping in carbon fibre film to give them the look,
they'll be light and look nice, but won't be as expensive or risky as the pukka carbon ones.
[Edited on 27/1/11 by B120WNY]
At the start of last season HRT were running steel wishbones with carbon shrouds. If its good enough for F1....
We make carbon wishbones at work for 2 top F1 teams.
£25k for a set of 4 anybody? please bear in mind that doesn't include
the titanium end fittings for mounting or the bespoke match fitted rose joints
for adjusting them, but does include X-rays of each component and full traceability
of all materials used.
They are, however, 10x stronger than any alloy steel ones , but as mentioned
earlier by others, only in the direction they are designed to work.
You go over a kerb at a race track or a pot hole on the road, they won't even blink...
Nudge one forward or backward though and they'll snap like a carrot. 
Joking aside, there's hardly any woven fabric in them. It's 90% UD (uni-directional)
material and hoop plies which are basically horse sshoe shaped hoops of UD
which go around each end and then fan out up each leg internallyy to load spread any pull
up the entire leg.
They are moulded in halves, 3D profile CNC machined, then bonded together in a bespoke
fixture in an Autoclave.
Woven is mainly used as edge trim to prevent spelching whilst machining them.
HTH
Nick.
EDIT: Forgot to say... the "Flexure" area of each leg is only 4.8mm thick!!!
[Edited on 27/1/11 by shaft]