philgregson
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| posted on 23/7/02 at 11:28 AM |
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Stiffness
I'm not an engineer or anything but the cabin does not look as if it would be particularly stiff due to its acres of large open space.
I was considering puting diagonal bracing in the transmission tunnel and plating with alu instead of steel. This would not be any heavier, but I was
wondering if it might be slightly stiffer.
Any thoughts?
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philgregson
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| posted on 23/7/02 at 12:13 PM |
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for 'would be particularly stiff' read 'would not be particularly stiff'!!
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David Jenkins
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| posted on 23/7/02 at 12:36 PM |
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Phil,
You would be wise to have a word with the aussie builders - they have some well-defined stiffening techniques.
David
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philgregson
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| posted on 23/7/02 at 02:44 PM |
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Which particular aussie builders are these, ans where would I find them?
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David Jenkins
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| posted on 23/7/02 at 03:03 PM |
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Damn - I knew you'd ask that! 
It's one of the Yahoo groups at
http://groups.yahoo.com/group/Locost_Oz/
You'll have to nose around from there...
The main point is that Oz builders have to pass strict tortional tests, so they've got really good at making the chassis more rigid without too much
weight penalty.
cheers,
David
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fastenuff
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| posted on 23/7/02 at 07:05 PM |
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also check out the photo erea. for the pictures of some of their xtras
Ingmar
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locodude
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| posted on 23/7/02 at 07:54 PM |
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Hi
Check Rob Lane's website at http://www.domsat.co.uk/pages/locost.htm as he's done the aussie mods on his car and there are photos etc.. I don't
belive they are necessary for the road though. Rob hillclimbs his car.
Chris (ptm)
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philgregson
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| posted on 23/7/02 at 09:50 PM |
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I've been and looked at the aussie mods and they seem to use tonnes of extra steel in places where, as you say, I don't think it is worth it for the
weight gain.
My original query about the transmission tunnel was based on the fact that I thought I might be able to gain a small amount of stiffness for no cost
weight wise.
I could see no attention paid to this by the aussies at all by which I can only assume that it probably isn't worth it.
Still can't get away from the fact that it just feels right though.
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Liam
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| posted on 23/7/02 at 10:30 PM |
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Hello...
I made balsa models of a standard chassis and my design. Triangulating the trans tunnel seemed to make a big difference to the stiffness of the cabin
area, which as you say is the worst part. Standard book engine bay aint great either.
My chassis has a structural scuttle (for safety as well as stiffness) and a removable frame over the engine (idea stolen from a TVR Tuscan racer and
needed cos my engine is so big I can't even put as much triangulation in the engine bay as a book chassis).
I use about 6kg of extra tubing, but then I'm using ali panels, including the floor, so my chassis should be no heavier than a book chassis.
A little bit of extra weight for a big increase in stiffness and/or safety is well worth it IMHO. You should only worry about the weight of a few
extra bits of steel tube if your going bike-engined and want to race it or something. Even a few metres of extra tube is nothing compared to a crap
ford cast iron upright, or sierra calliper for example.
Enough rambling - short answer: triangulating trans tunnel is good for stiffness.
Liam
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philgregson
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| posted on 24/7/02 at 07:52 AM |
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Triangulated transmission tunnel it is then!
I was also looking at building a structural scuttle - not only to improve stiffness (a by product really) but also to improve the chances of retaining
my legs etc, should I be stupid enough to drive into something solid or (worse still) get 'T boned'.
It would apear that you are also using alu sheet for the floor - I presume you have triangulated that as well?
All my weight calculations so far would tend to indicate that the weight saving by using alu sheet in a given area will pay for a tube or two to
assist stiffening and (I stress that I can provide no engineering proof for this) it would seem to me that diagonal bracing with tubes is normally
going to be stiffer than plating.
I have always thought that with these things that if it feels and looks right (and bracing does) it possibly is right, although I still treat this
principle with some caution lest I make a right pigs ear of it all - hence the continuing questions.
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cymtriks
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| posted on 28/7/02 at 09:38 AM |
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Take a look at my chassis ideas on the "mcspeedy - chassis poll" on this site. These mods produce a 100% stiffness gain and a 10% reduction in
chassis weight. These mods will influence assembly so check that your parts are not fowled by the additions. The Oz mods do increase stiffnes but are
no where near optimum, I reckon they just bodged it until it passed their requirements. Do not plate the tunnel with alloy, it won't make anything
like the difference you hope for and may make things a lot worse. By far the best tunnel mod is to box it in completly on all four sides with welded
steel sheet, 18 gauge will be fine. This will also be easier than triangulation. You are correct that the driver and passenger area is a bit low on
stiffness but the big gains come from extra bracing around the front suspension as in my suggested mods. Just in case you are wondering I'm using the
same computer analysis techniques as the major manufactures use for their structural analysis. Good luck with the build.
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cymtriks
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| posted on 28/7/02 at 09:39 AM |
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Take a look at my chassis ideas on the "mcspeedy - chassis poll" on this site. These mods produce a 100% stiffness gain and a 10% reduction in
chassis weight. These mods will influence assembly so check that your parts are not fowled by the additions. The Oz mods do increase stiffnes but are
no where near optimum, I reckon they just bodged it until it passed their requirements. Do not plate the tunnel with alloy, it won't make anything
like the difference you hope for and may make things a lot worse. By far the best tunnel mod is to box it in completly on all four sides with welded
steel sheet, 18 gauge will be fine. This will also be easier than triangulation. You are correct that the driver and passenger area is a bit low on
stiffness but the big gains come from extra bracing around the front suspension as in my suggested mods. Just in case you are wondering I'm using the
same computer analysis techniques as the major manufactures use for their structural analysis. Good luck with the build.
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