MONOCOQUE INFO ??

[Rob Davies]

Well i'll be moving onto the chassis next year and I thought it would be cool to make a monocoque chassis (or atleast partly) but ive been told by the lecturers its far too hard and we should stick with steel.
Just wondering if anyone has got any info on design (prob on ansys) and construction of these things.
If we can come see some teams in England that would be great. If not for a road trip, would be good to see the possibilities.
If we dont come up with a convincing argument for a moncoque by a week friday...itll be space frame for us - and itll be nice to do something different than the last 4 years.

Cheers, Rob

[Rob Davies]

Well i'll be moving onto the chassis next year and I thought it would be cool to make a monocoque chassis (or atleast partly) but ive been told by the lecturers its far too hard and we should stick with steel.
Just wondering if anyone has got any info on design (prob on ansys) and construction of these things.
If we can come see some teams in England that would be great. If not for a road trip, would be good to see the possibilities.
If we dont come up with a convincing argument for a moncoque by a week friday...itll be space frame for us - and itll be nice to do something different than the last 4 years.

Cheers, Rob

[Ashley Denmead]

Rob,

Dont let your lecturers tell you its "too hard" monocoques are really quite simple and very quick to construct if designed properly.

[Mi_Ko]

Can someone tell us, the space frame teams, a aproximate costs for the monocoque material?

How many epoxy have you used, and how many carbon fiber cloth?
How many layers do you normaly use for the monocoque?

[Rob Davies]

What about carbon fibre stressed skin...

not too sure on what this is and how it is achieved but ive heard a few people talk about it.

i can guess that it increases the stiffness of the chassis by being incompressible between each member of the frame. but is easier to make than a monocoque??

Cheers, Rob

[Charlie]

I am not an expert on Monocoques. But I do know steel space frames aren't the easiest thing in the world to fabricate for sure.

I would guess that people stay away from Monocoques because they don't know how to get started, while its a lot simpler to visualize a steel space frame. I would expect it takes a lot of practice and testing/learning to develop your monocoque process. Of course it also takes testing and learning to figure out how to build a space frame, especially to a high level of accuracy.

A stressed skin space frame seems like it would be like building a space frame + extra work that at least touches on monocoque construction.

So far all you've been interested in is how easy each one is to build. I would try to at least estimate which is the better option (hypothetically, and also given your team's resources), because it has been proven that you can do either in the year's time.

[Rob Davies]

Well for sure a carbon fibre monocoque is gonna be the way to go, so thats the hypothetical answer.

Steel space frame is easier for us as we have designed and constructed this for the last two years. But we are thinking we may have gotten to our limit with space frame.

Carbon fibre has never been used before by us, and the lecturers dont want to make the jump in one year, but my view is they are gonna have to make the jump this year than any - so thats why im trying to get some info.

Prob end up dabbling in carbon fibre with the non structural parts.

Of course the setup at our uni means this is my first and final year on the car (as is the rest of the team) so forgive me for not having a clue on certain points

Cheers, Rob

[Charlie]

Well I wouldn't assume that carbon is the best answer not considering production and cost issues. In my (limited)experience, it seems like the carbon cars have a bit more weight for a given stiffnes vs. a space frame. Of course the advertised stiffnesses and weights of most of these cars can be questionable, and the monocoque might save weight elsewhere (body for example).

I'm sure UW or UWA could give good advice on this, as both have recently developed monocoques in place of space frames. If they don't respond here, I would try and contact them privately (sorry guys http://fsae.com/groupee_common/emoticons/icon_wink.gif )

[Eddie Martin]

Well it all depends on what suits your team. As a team you should always play to your strengths. Whether it's good welding equipment, cnc facilities or a generous composites sponsor.

There are advantages to monocoques like being potentially lighter and stiffer than equivalent space frame, less weight because of reduced body work and firewalls, maybe quicker to build for your team.
There are also disadvantages like complexity of passing structural equivalency, maintenance (can be very hard to work on parts of the car), ergonomics (while I haven't seen every monocoque the ones I have seen wont fit larger people).

I'm sure there are more arguments both ways, it all comes down to what suits your overall car package best.

"Don't let University get in the way of your education"

[MikeWaggoner at UW]

Monocoques can be made in a whole bunch of ways. At WWU, we made monocoques with two tubes used for torsional rigidity. The tubes were held together with aluminum bulkheads. The chassis was easier to manufacture than a spaceframe (I helped on a simple Mini Baja chassis the year before), but packaging was a problem. The chassis weighed 44 lbs. dot.etec.wwu.edu

Another car at WWU, Viking 32, was a cut and fold monocoque. They took flat carbon/aramid/carbon panels and cut grooves in them. The folded the grooves and wet-laid carbon in those areas. This can also be done pretty quickly.

At UW last year they made one by producing a plug, and laying up high temp wet carbon fiber on it. The high temp carbon was then used as a mold for pre-preg. The chassis team worked like dogs for months on it. This is the way to theoretically achieve an ideal structure, but I think it's too much work.

The lightest (with adequate stiffness) spaceframes seem to be around 65 pounds, and I think a monocoque could come in around 40 lbs (mainly because of steel safety requirements). The steel car will also need a body. I haven't seen many carbon monocoque cars that are that light, just because designed things from carbon is difficult.

As far as cost, guess 40-60 pounds of carbon X $100 and see what it does to your cost report.

-Mike Waggoner

[Charlie]

I might be wrong but I want to say Cornell's space frame weighed in the low 50 lbs (advertised) last year. Perhaps someone from there can verify that. Our 2003 car was 61 lbs and 1900+ phyically tested frame rigidity. Our 2004 car was 56 lbs and 1600+ tested frame rigidity. I think all the good cars are stiff enough and under 60 lbs frame weight for sure.

[Ashley Denmead]

My 2cents.....

why dont you consider the overall concept of the comp (1000 cars per year)......once you have a female mould of your chassis you would be able to bang out chassis in no time at all! something to maybe consider when justifying your design choice!

and in my opinion a monocoque is a whole lot easier to build accurately than a spaceframe and will inherantly be stiffer and lighter than the equivilant spaceframe. A good monocoque should be optimised just like a spaceframe should be....no point having 10 layers of carbon in places that dont need it!

[Travis Garrison]

Why does everyone ignore the aluminum monocoque? Seems like the logical choice to me...easy to manufacture....slight specific stiffness advantage over steel, and dirt cheap...Not to mention you can actually FEA an aluminum chassis.

I would caution teams with little composites experience that if you try to teach yourself by building a chassis...it will look like you were trying to teach yourself by building a chassis. Layups are not at all difficult but they do require some skill. Break yourself in with test laminates or smaller parts (intakes, wings, etc...) Pay attention to draft angles, release agents, and EXACTLY how you plan on bagging your part.

Enough rambling...

Travis Garrison

[Lyn Labahn UW-Madison]

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Travis:
Why does everyone ignore the aluminum monocoque? Seems like the logical choice to me...easy to manufacture....slight specific stiffness advantage over steel, and dirt cheap...Not to mention you can actually FEA an aluminum chassis.
<HR></BLOCKQUOTE>


*Cough*
http://homepages.cae.wisc.edu/~sae/frame/frameconstruction2.jpg


We have ran a 7075 aluminum skin center section the last 4 years...our car weighed 455 this year, and I believe the weight saved in body work was a large factor in getting below the 470-480ish average that most top teams run.

[BryanH]

That's intriuging construction but doesn't appear to be classic alloy mono which is totally riveted ALL Aluminium

I have a Ralt RT4 in the workshop which has a new tub. I will take some photos & post them

I agree with Travis.It is part way towards the advantages of carbon tub and is very do-able by anyone with sheet metal tools and very satisfying to make. Carbon needs serious expertise.

[Rob Davies]

Well thanks for the info guys

Its good to see that because we cant make carbon fibre we are not at such a disadvantage

What do these aluminium frames typically weigh?

[Travis Garrison]

Lyn,

I know, I know...you guys do a hybrid monocoque...and Queens U from up north goes a even further with only a spaceframe in the rear...I just meant that people hear monocoque and they automaticaly think composites.

455 lbs and no layups makes a pretty strong argument for your technique...Any figures on your chassis weight?

Travis Garrison

[Lyn Labahn UW-Madison]

Travis,

The completed frame weighed 61 lbs, and had a stiffness of ~1700 lbf*ft/deg between the bellcranks. This was the first frame designed by the co-designer and I, after looking back on it and optimizing a few wall thickness and other items, I believe the design could achieve a weight of around 56-58lbs while maintaining a similar stiffness value.

[Rob Davies]

apperently our car is 5000 N.m / degree stiffness

i convert this to 'english' units and get 3600 lb.ft / degree

this seems a factor of 2 out but im not sure if its the measurement or my conversion. Any advice?

space frame weighs in at 30kg btw

[Lyn Labahn UW-Madison]

Sounds a little high Rob, perhaps your measurement technique is different than is commonly used.

[Rob Davies]

our fourth years told me it was diagonally from the front to rear axle

apparently this is worst case scenario for the chassis

is this the commonly used measurement?

Thanks, Rob

[Lyn Labahn UW-Madison]

I am not sure I understand what you are talking about. Was the load applied through the suspension by replacing the shocks with deadlinks?

[Rob Davies]

well we can see I have no clue what I am talking about!

How are you supposed to calculate it then?

[RiNaZ]

Is any team working on making a monocoque chasis (aluminum or carbon) anytime this summer or fall? I was thinking maybe me and my team can do a field trip over there.