Rorty
|
| posted on 15/12/04 at 06:07 AM |
|
|
quote:
Originally posted by kb58
Yeah but I meant TUBES, as in monocoque aluminum ones, of a foot in diameter or more, as in old F1 chassis. The fuelcells were put inside the side
pods. Staniforth reviews this chassis type.
I know, I was just being a twit. 
Cheers, Rorty.
"Faster than a speeding Pullet".
PLEASE DON'T U2U ME IF YOU WANT A QUICK RESPONSE. TRY EMAILING ME INSTEAD!
|
|
|
|
|
Sven
|
| posted on 15/12/04 at 10:07 AM |
|
|
You fellas is just being silly ... a pyramid with 4 wheels would be much more practical ... 
-Sven
|
|
|
Mave
|
| posted on 15/12/04 at 04:21 PM |
|
|
quote:
Originally posted by Aloupol
Yes of course it is.
For a EPN100 as instance (height 100 mm and width 55 mm) the flanges are 5.7 thick each and the web is 4.1 thick. So the moment of inertia is about
50% more than the equivalent tube.
Please explain what you mean with equivalent tube. In this case, my equivalent tube would be 100x55, with 55 sides being 5.7 thick, and the 100 mm
sides being 4.1/2=2.05 thick. In my book, that equates to the same moment of inertia. Or am I missing something?!?
By the way; I like the I-beam chassis! Kind of provides the same characteristics as Dax camber compensation system, right? 
|
|
|
DaveFJ
|
| posted on 15/12/04 at 04:54 PM |
|
|
now this is just getting silly....
what you want is a 'real' chassis - like this one.... (definition of 'real' - lots of tubes and the more complicated the
better!)
[Edited on 15/12/04 by protofj]
Dave
"In Support of Help the Heroes" - Always
|
|
|
ettore bugatti
|
| posted on 15/12/04 at 05:14 PM |
|
|
He, somebody did extensive google work here!
Gordon keeble, isn't it?
|
|
|
Aloupol
|
| posted on 15/12/04 at 06:19 PM |
|
|
quote:
Originally posted by Mave
Please explain what you mean with equivalent tube. In this case, my equivalent tube would be 100x55, with 55 sides being 5.7 thick, and the 100 mm
sides being 4.1/2=2.05 thick. In my book, that equates to the same moment of inertia. Or am I missing something?!?
Mine would have equal thichness all around, as all the things called "tube" I met so far.
[Edited on 15/12/04 by Aloupol]
|
|
|
DaveFJ
|
| posted on 15/12/04 at 08:03 PM |
|
|
quote:
Originally posted by ettore bugatti
He, somebody did extensive google work here!
Gordon keeble, isn't it?
Full marks!
And what a car! - it's pratically a kit car anyway (steel spaceframe with full GRP bodywork and a humming V8) I just wish someone would actually
start making a Kit (far beyond my skills to do this from scratch)
When you look at the specs of this car it was literally light years ahead of it's time,
So Please Santa - if your reading this - i've been really good this year honest!
fidn out more HERE
[Edited on 15/12/04 by protofj]
Dave
"In Support of Help the Heroes" - Always
|
|
|
Mave
|
| posted on 15/12/04 at 08:51 PM |
|
|
quote:
Originally posted by Aloupol
Mine would have equal thichness all around, as all the things called "tube" I met so far.
[Edited on 15/12/04 by Aloupol]
Ahh, with that definition of a "tube", you're right of course, and I stand corrected. I'm just thinking in "designed
cross-sections". (I'm used to working with composites, so I can finetune the thicknesses throughout the circumference).
However, it's not an entirely honest comparison, as the weight of both beams would be different too......
Ahh well........so much for theory!
|
|
|
fester
|
| posted on 17/12/04 at 05:24 PM |
|
|
second moment of area
the reason that construction uses I section beam is that,when a bending moment is applied,one surface is in comression and the other is in
tension.This means that between these two forces is a "null point" which is neither in compression or tension;so there's no need for
large amounts of material here.Try bending a ruler on it's flat then on it's edge.
All an I section beam is doing is holding the two forces apart and connecting them.
I section beams are useless in torsion,though:hence the need for box section.
|
|
|
Volvorsport
|
| posted on 17/12/04 at 05:48 PM |
|
|
re: gordon keeble - looks like a gilbern invader , now theres a car i could certainly live with , i aways like the angular styling - Anybody got one
so i can copy it ?
www.dbsmotorsport.co.uk
getting dirty under a bus
|
|
|
kb58
|
| posted on 17/12/04 at 06:24 PM |
|
|
quote:
Originally posted by fester
the reason that construction uses I section beam is that,when a bending moment is applied,one surface is in comression and the other is in
tension.This means that between these two forces is a "null point" which is neither in compression or tension;so there's no need for
large amounts of material here.Try bending a ruler on it's flat then on it's edge.
But in that same analogy the ruler is very poor torsionally... that's why tubes work so well.
All an I section beam is doing is holding the two forces apart and connecting them.
I section beams are useless in torsion,though:hence the need for box section.
[fixed quote]
[Edited on 12/20/04 by kb58]
Mid-engine Locost - http://www.midlana.com
And the book - http://www.lulu.com/shop/kurt-bilinski/midlana/paperback/product-21330662.html
Kimini - a tube-frame, carbon shell, Honda Prelude VTEC mid-engine Mini: http://www.kimini.com
And its book -
http://www.lulu.com/shop/kurt-bilinski/kimini-how-to-design-and-build-a-mid-engine-sports-car-from-scratch/paperback/product-4858803.html
|
|
|
silex
|
| posted on 19/12/04 at 05:28 PM |
|
|
Got board at work this morning so I knocked up this Excel Spread sheet which calculates the "Second Moment of Area" for a number of
different tube sections.
It is only very basic, but if people find it useful then I may expand on it, or other people can have a go if they want - its not like its copyrighted
or anything.
I-Value.xls
The formula are from memory (ooh err) so if anyone spots a mistake, please let me know - I didn't get much time to check it.
Cheers.
Murphy's 2 laws
1. If it can go wrong it will
2. In case of emergency - refer to rule 1.
|
|
|
Peteff
|
| posted on 19/12/04 at 08:01 PM |
|
|
holding the two forces apart and connecting them.
Which is it doing, holding them apart or connecting them? It can't be doing both . I still don't understand this thread.
yours, Pete
I went into the RSPCA office the other day. It was so small you could hardly swing a cat in there.
|
|
|
silex
|
| posted on 20/12/04 at 06:26 AM |
|
|
I will try to explain it without wading into the engineering math.
Lets say you have a piece of steel, its 30mm wide, 5mm thick and 1000mm long. You lay this flat on the bench so that you can clamp 500mm to the bench
and let 500mm overhang the bench. Now if you push down on the very end of the steel thats unclamped and overhanging the bench and you will bend it
very easily. I am sure you will have probably done something like this in the past.
Now repeat the experiment, but this time put the steel up on its edge and see if you can bend it - probably not, but you still have the same piece of
steel so whats changed ?
You could try this quickly using a ruler on a desk.
The " I " value (second moment of area) makes up part of a formula that helps us determine how much force can be applied for the steel to
bend. The bigger the " I " number, the more resistant it is to bending.
[Edited on 20/12/04 by silex]
Murphy's 2 laws
1. If it can go wrong it will
2. In case of emergency - refer to rule 1.
|
|
|
Peteff
|
| posted on 20/12/04 at 09:47 AM |
|
|
Right then,
So the shorter the piece the higher the value? If you look at a chassis with all the different lengths and the way they interact it must be a
nightmare to work out.
yours, Pete
I went into the RSPCA office the other day. It was so small you could hardly swing a cat in there.
|
|
|
fester
|
| posted on 20/12/04 at 07:11 PM |
|
|
second moment of area
Hi,Paddy;
No, when you talk about "overhang" you are really talking about "bending moment" when you talk about "second
moment of area" you are talking about resistance to bending moment of a given cross sectional area(remember the ruler analogy).....And
yes,it's a complete B*****d to get your head round.I,m glad I,m not in collage no more!
|
|
|
sgraber
|
| posted on 30/12/04 at 02:55 AM |
|
|
quote:
Originally posted by Wadders
Mmmmh, after careful evaluation of all the expert advice posted on this subject, opinion seems divided as to the strongest method of construction, so
iv'e decided to modify my design a bit. Check it out, and be amazed. Cunning in the extreme even if i say so myself.
http://locostbuilders.co.uk/photos.php?action=showphoto&photo=2rsj%20chassis.jpg
I am very impressed by your use of 1/2" steel plate to box in that massive I beam. That should make it nice and strong.
Steve Graber
http://www.grabercars.com/
"Quickness through lightness"
|
|
|
Peteff
|
| posted on 30/12/04 at 09:53 AM |
|
|
So....
the bending moment is the edge of a desk if your ruler is flat and the second moment is when you turn your ruler over, or ten past three or something.
I give up now.
yours, Pete
I went into the RSPCA office the other day. It was so small you could hardly swing a cat in there.
|
|
|
JoelP
|
| posted on 30/12/04 at 11:14 AM |
|
|
your teachers must've loved you at school pete... an uncooperative pupil
in my foolish understanding, square tube is very similar to I-section beams. Except that the tube is 'evened out' so that it isnt as fussy
as the I section. i suspect that I-sections are only good at resisting bending in the one plane, and that is bent on their side they wouldnt be great
- certainly less resistant to crumpling than a square tube.
this thread is really scrapping the barrel, isnt it? i almost wish i wasnt about to continue it.
Beware! Bourettes is binfectious.
|
|
|
