Goto builds then alum....
Alumium frame
Goto builds then alum....
With my admitted limited knowledge, it's a very bad idea. Aluminum work hardens, every bump makes the chassis more brittle - cracks are
guaranteed. Anyone who uses aluminum structurally doesn't weld it, instead bonding or rivetting. Lotus for example. Airliners...
Just because someone's done it doesn't make it a good idea. Let's see a status report on this aluminum car after it's been
driven 15,000 miles...
I am very curious to know what sort of torsional stiffness figures they are expecting from that chassis. Appears some of the tubes have been
substituted for larger widths and some have been added.
I suppose they think that will compensate.
Hey man I am with you!!
Notice the
quote:
Originally posted by Jermyn
I am very curious to know what sort of torsional stiffness figures they are expecting from that chassis. Appears some of the tubes have been substituted for larger widths and some have been added.
I suppose they think that will compensate.
Ali is 1/3rd the stiffness of steel...ergo you need 3 times the amount of material to get the stifness back. So an ali chassis will weigh the same as
a steel one (for spaceframes anyway).
As already stated, its not advised to create welded chassis' in ali, unless you have the facilities to heat treat a whole chassis when its
finished!
David
in the early eighties i used to race a tz350 bike with a spondon ali frame
very light but it used to crack around the headstock area from this limited esperance i wouldent use ali for a chassis
good luck dave
Another aluminium spaceframe.
Aluminium is 1/3 the weight of steel but also 1/3 of the stiffness so copying a steel frame design in aluminium gives a big stiffness loss and a big
weight reduction. To get back the stiffness you have to triple the tube wall thickness which triples the weight. This brings you back to the
structural properties, weight and stiffness, of a steel frame but at greater cost, lower fatigue life, and more difficult welding.
Avoid.
Oh I wasn't going anywhere near it!! Just figured I'd spark a discussion...
I won't bother commenting on the use of ally, think we're all decided it's a bad idea, but the name made me laugh - ESTfield - how
original!
Pete
I hope they have video of the first time they floor it, That chassis will twist like a pretzel!!
Well the current analysis isn't right quite yet.
You can make a chasis from ali more stiffer then one from steel. But then you need to use larger diameter tubes because the diameter of a tube gives
more strenght to the construction.
But i think that if the steel tube = 25mm round. you will need ali round 40 or something like that.
you still would be less weight.
Thats pure the construcition vision i have.
But offcourse welding a complete chasis isn't a good idea....
Lotus uses a glue for their chasis etc. the main reason is because of if you weld ally it is weaker after it on the place you welded it. Glueing
doesn't affect it.
I think the best conclusion we need to do is that a ali construction is very expensive
(material, glue) because if a dry chasis will weight 130Kg i think you need 100Kgs of ali...
Another good idea would be welding it in INOX (stainless steel)....
TKS
What "current analysis" are you talking about? The book chassis was designed without any analysis. Analysis using FE has been done by me and
by Wesley. My analysis and his are both posted in the files section of the locost7.info site. The steel chassis can be greatly improved fairly
simply.
Using larger diameter tubes will improve the stiffness of the tubes for the same weight but the effect on overall chassis stiffness will be small. In
a spaceframe the tensile properties of the tubes are much more important and as alluminium has 1/3 of the stensile properties of steel you cannot get
a weight saving for the same stiffness.
For a ladder frame, in which the stiffness of the tubes is directly related to the overall stiffness then you are correct. A larger tube in aluminium
will give a better stiffness for a given weight than steel tubes.
Construction in aluminium isn't that expensive. You need to clean and etch every joint before you apply the glue to get a good bond.
The lotus Elise chassis is not a spaceframe. It is actually close to being a ladder frame as its structure is dominated by those two big tubes that
form the sills. I have described the Elise as being a hybrid of ladder frame and monocoque in my analysis and I still think this a good description of
how it works.
Aluminium spaceframes are gimicks. Aluminium ladder frames or monocoques can work very well if they are designed properly.
I think part of the issue is that a true space frame puts *no* bending loads in any tube, only tension or compression. For that reason you can use
tubing only large enough to resist buckling under compression. OTOH, if you have tubes that will only see tension loads, you could use very small bar
stock... or even cable.
Anyway, seems it's best for us to stick to old-school construction practice and stay with steel.
I ride an aluminum mountain bike that is basically a super stiff, super light space frame. The stress that the frame goes through must be really high considering the way I ride. Translating bicycle frame design to a car would be extremely complicated and expensive. The tubes on my Klein bicycle are very large diam. but somehow they thin the walls down to nearly beer can thickness in the middle of the tube and leave it thick at the ends where it is welded. I would guess that if this was practical in a car one of the exotic car companies would have tried it allready. If that frame wasn't heat treated after it was welded I would run from it.
There must be something in the ally chassis idea or you wouldn't get the likes of audi, jaguar an lotus making production cars out of it - cars
that have to go hundreds of thousands of miles without they're chassis falling apart!
I do agree with cymtriks tho, from all the evidence i've heard ally spaceframes seem well dodgy.
maybe someone will get round to making a locost ally monocoque? (other than Robin Hood and the famed cheesegrater!)
cheers
The problem isn't ali as a chassis but rather WELDED ali SPACEFAME. Welding ali isn't clever for strength (becomes brittle) and I'd
much rather trust steel when my ass is 4" from the ground at 70mph
[Edited on 13/3/05 by chunkielad]
Isn't Ron holding up an MK built ali chassis on page 53 of "BOOK" no 2?
Pretty sure that's steel mate.
ally monocoque survive in oz - theres been a few threads about them .
A pared down race chassis could not be compared with a production car .
quote:
Originally posted by chunkielad
Pretty sure that's steel mate.
Why did MK and Ron do it then?
Don't know but I suspect RC thought it would work.
I spent a month of my proffessional life sorting out somebody elses design for a manhole lifting made out of similar but larger (2"x2" )
aluminium extrusion. The corner welds had been failling on almost every machine after a couple of months use . I raipdly came to the conclusion -- it
just wouldn't work and needed a complete rethink. I redesigned it based on 2.25" tube and 2.5" H section extrusions. Although the
weight went up from 18kg to 25kg after that we had only one failure and that was due a deffective extrusion.
It taught me very valuable leasons
(1) a structure that works when made in steel usually can't be translated straight in to a light alloy.
(2) the importance of good weld design.
(3) aluminium structures fatigue
[Edited on 14/3/05 by britishtrident]
quote:
Pretty sure that's steel mate.
I believe the ally chassis was made as a show piece only.
Ned.
quote:
Originally posted by Ian Pearson
quote:
Pretty sure that's steel mate.
Have you tried lifting your steel chassis?
I move it out of storage when I work on it and lift it back after.
quote:
Originally posted by chunkielad
quote:
Originally posted by Ian Pearson
quote:
Pretty sure that's steel mate.
Have you tried lifting your steel chassis?
Yes and it's no problem!!
I am looking in to monocoupes at the moment and there construction. A book on aerospace structures was recommended does any one else have a good source of information on this type of structure and how they are designed?
I'd like to find out a little info on building monocoque chassis, not for a 7 but for a different project.
I've always been of the impression that you had to be an engeneer to design one, but if there are a few simple rules to follow then I'd be
all over it.
i made a aluminium chassis it was a lot lighter than steel one by a lot pics on photo archive
I just hope that isnt for a road car, and that you know the life expectancy of the chassis! It looks to be a book chassis, so will not be very stiff either. Though it will function, dont expect it to last for many hours use without major fatigue problems....