maartenromijn
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| posted on 30/10/08 at 02:16 PM |
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Sorry, off topic
quote:
nooo, didn't design it myself. its an ex race car. similar suspension etc to a 7 though, but uses a watts linkage at the back.
Is it already race-able? Do you notice a difference between a watts-linkage and a panhard rod? (I mean in road-holding).
BLOG: http://thunderroad-super7.blogspot.com/
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blakep82
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| posted on 30/10/08 at 02:19 PM |
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i haven't driven it yet, nor have i driven a car with a panhard rod, so haven't had a chance to feel the difference between the two. on
paper a watts linkage looks best though, but give there shouldn't be too much suspension travel, i'm not sure it would have made a
noticeable difference really
________________________
IVA manual link http://www.businesslink.gov.uk/bdotg/action/detail?type=RESOURCES&itemId=1081997083
don't write OT on a new thread title, you're creating the topic, everything you write is very much ON topic!
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Fred W B
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| posted on 30/10/08 at 02:32 PM |
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My opinion - The advantage of using the high strength steels is that you can use a thinner tube, therefore lighter.
If you don't mind a thicker heavier tube a less esoteric grade of steel could be used, which is also cheaper.
Note I don't quote actual thicknesses and sizes, that's for each person to decide for himself, as stated above
And that also depends on what you can source and get bent decently. If you have to join, a properly welded joint, WITH A SLEEVE INSIDE, should be as
strong as the original material.
Cheers
Fred W B
[Edited on 30/10/08 by Fred W B]
You can do it quickly. You can do it cheap. You can do it right. – Pick any two.
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procomp
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| posted on 30/10/08 at 02:38 PM |
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Hi.
The thing is that FIA and in this country MSA governed by the FIA regulations are always being updated. There where new regulations introduced during
2004. And again for the start of 2008. ( not that many manufacturers seem to be tacking any notice )
Having not so long ago had to put a roll cage through the latest testing procedures which now takes into account not just the roll cage but the whole
chassis and the distribution of the loads through out the chassis you soon see where and why strict regulations need to be in place.
There is already far too many companies and manufacturers who are selling so called cages / bars that they believe comply with certain regulations but
the truth is they do not even comply with the bare basics never mind passing the regulations. Hence there are more and more motor sport competitors
being told that the money that they have just spent was wasted as they now have to have a new setup to comply.
As it stands for sports cars not single seaters the larger diameter cages of 1 3/4" are allowed to be used but must follow the drawing in the
blue book. Any cages / bars that are of smaller diameter must have been fully tested and certificated by the FIA / MSA if being used in the UK. IF in
any doubt seek clarification from the MSA.
The reason there is such regulations is because there are individuals out there who would still rather have a cage / bar made of 1 1/2" dia and
16g to save weight rather than something that will save there life during a big accident. Then there are the cages that turn up where the desighn is
sound but assembled with clamps that are of no use or welding that would never hold up.
As has already been said the choice is yours but i would rather enter a situation knowing i had done my best rather than having that nagging doubt
that it may not save my life.
Cheers Matt
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Ian-B
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| posted on 30/10/08 at 08:09 PM |
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To answer some of the points in the original post
The logical explaination for requiring seamless tube and contiunous unwelded main hoop would be to minimise the risk of creating additional failure
points. The main reason for requiring a more substatial section of material than often used of the chassis is the the roll hoop is far more likely to
receive a direct point load a significant distance from a join and most roll structure designs have no/little redundacy in the structure.
For the load cases you describe;
1 - Normal roll over, the loads are generally fairly modest, to compare to production road cars where there is currently very little roll over
legislation, the USA (only reg I am aware of) specify a maximum displacement for a load equivalent to 1.5x vehicle mass, which is shortly to be
increased to an expected 2.5x vehicle mass, this is far lower than normal motorsport specifications (approx 7.5x vehicle mass from memory), yet most
road cars will provide reasonable protection to a straight forward roll over.
The main reason for needing a higher specification is for combined roll and modest impact on the roll structure (eg rolling as a result of being
launched to reasonable height), for which the risk of this load case is fairly high in motorsport.
2 - For side impact, this as far as I can tell from the current blue book this is not really covered effectively, with many roll structures built to
the regulations often being far from ideal at providing protection My reasoning for this is that the regulations focus is on static strength (with
only a vague comment on elongation properties) and many of the available CDS grades obtain the required tensile properties through the cold working
which results in a very siginificant reduction ductility (best tubing to use for this type of application is one where the base grade of steel is
adequate to achieve the required yield stress, allowing the tube to be used in the normalised condition giving good ductility, but more expensive).
By way of example, for a load applied to the centre of typical side impact bar even when made from larger of the MSA standard spec tubes would only be
able to resist a few G acceleration on a typical 7 type car before yielding, once the tube starts to yield providing there is adequated ductility the
tube can still help absorb significant energy by acting as a tension member transfering forces into the main structure. For low ductility tubes the
failure of the tube will often occur prior to any substantial engery absortption, resulting in very large intrusions into the passenger space.
If designing a roll structure for an application where specific material specifications aren't required there is nothing wrong with using a
seamed tube, to use the production car comparision again, in cases where tubes are used in crash relevant parts the decision as to whether the tube is
welded or seamless is usually determined by the most effective means of manufacture and the weldability of the steel being used.
The design of the structure and its mounting to the main vehicle structure, are more significant in the determining the effectivness of the structure
in protecting the occupants, than the manufacturing process of the tube used.
If however you are building with any intention of racing the car, then you need to use the specified materials / layouts (unless you get your design
approved MSA/FIA), but consider that just because it meets the specification does not neccesarily mean it will be fit for purpose. Also not all racing
cages are specified to particularly large section or high strength tube, if you are racing in a series where the requirements specified are those for
non standard cars then the min is 32mm dia 1.5mm*** wall good quality seamless steel tube effetively braced for and aft of the cockpit
***Changed for 2009 - allowance for different material specs from C(C)39 & 41 removed all cases except single seater and sports racing cars tubing
45x2.5 or 50x2mm min yeild 350MPa.
[Edited on 27/11/08 by Ian-B]
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Ivan
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| posted on 31/10/08 at 06:51 AM |
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Thanks Ian-B - you answered most of my questions very well and have given me a much better understanding of the issues.
I guess that's why we post here - there's always someone with a much deeper understanding of the subject to answer us.
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Ninehigh
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| posted on 3/11/08 at 01:55 AM |
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I'll put it this way:
If you plant your car into a wall head on what part of you are you going to injure? Head, legs?
What about if you get rammed from your side? Arm, ribs, pelvis?
And then if you roll over, head and neck?
Which one is going to kill you most times of ten?
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