iank
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| posted on 15/6/06 at 11:59 AM |
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One way of losing a lot of weight is going 3 wheeler. Tadpole style are aerodynamic as well.
Mescherschmit style 2 in-line also saves a lot of frontal area.
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silex
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| posted on 15/6/06 at 12:05 PM |
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To get a decent weight reduction on the space frame / ladder you would have to move to a much thinner tube wall thickness.
For example,
35mm diameter round tube with a wall thickness of 0.9mm would have approx the same bending and tortional strengths as 25x25x1.6 square tube, but the
round tube would be approx 32% lighter
35mm dia x 0.9mm = 0.757kg/m length
25 x 25 x 1.6 = 1.176kg/m length
However, this will come with its own set of problems - welding the thin wall, mounting brackets are easier to tear off, the tube dints more easily
which could lead to stress raisers, etc.
You would probably be better off following some of the other suggestions and trying a few other concepts rather than keeping with a ladder type
structure.
Murphy's 2 laws
1. If it can go wrong it will
2. In case of emergency - refer to rule 1.
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cymtriks
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| posted on 15/6/06 at 10:08 PM |
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quote:
Originally posted by JonBowden
I might be missing something but isn't a ladder frame a rather poor choice for a very light car. Wouldn't a monocoque be better. Eg:
folded and rivited aluminium (like a Le Mans style car but smaller)
fibreglass monocoque
wood monocoque - I believe that Frank Costin made an F2 car called the Proteus as a wooden monocoque.
I just can't see a ladder frame being strong and stiff and light (at least not sufficiently for a car designed to be very light). Also, since
all the strength is in a plane near ground level, if you were hit by another car, none of the chassis strength could be used to prevent the bumper of
the offending vehicle hitting your body.
Yes a monocoque would be best but don't believe all the hype surrounding spaceframes vs ladderframes, most spaceframes are not stiffer than a
simple X braced ladder of the same weight and even well designed spaceframes will only beat ladderframes by about 5 to 10 percent for the total car
weight.
What sort of car is being considered here?
Two seater?
Four seater?
Take a look at the solar powered competition car designs, very aerodynamic and futuristic.
Another starting point could be a small sports car, Fiat X-1/9, for example, take molds of the bodywork and fit a turbo deisel for a compact, sporty,
light weight and very economical car.
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DIY Si
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| posted on 15/6/06 at 10:16 PM |
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Will you be having any body work at all? If so, what type, ie just a bit to keep the worst of the rain off, or a full shell? To save a little weight
here you could use the same/similar fabric to that used on old plane wings, the heat shrink kind of thing. you'd only need minimal supports for
it then.
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smart51
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| posted on 16/6/06 at 07:03 AM |
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It is a 2 seater and will have full bodywork for aerodynamics. With only 23 BHP to play with, you have to make the most of it if you want any kind of
top speed.
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JonBowden
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| posted on 16/6/06 at 08:35 AM |
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cymtriks, I accept what you say about ladder frames but we're looking for something close to the ultimate to achieve the design goals.
Jon
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smart51
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| posted on 16/6/06 at 09:32 AM |
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lowest weight not ultimate stiffness is what is needed to meet the design, and low cost if possible. The car is not going racing and will not be
driven at high speeds due to the engine or corner at high speeds due to the tyres.
Strong enough - as light as possibe - cheap. Simple is also good. If there are two equally good designs but one uses 30 tubes and the other 50
tubes, simpler is best.
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DIY Si
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| posted on 16/6/06 at 09:37 AM |
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What sort of dimensions are you looking at for this? If it's going tyo be quite small, ie smaller than a locost, would a simple rectangular
chassis with x bracing be sufficient? Or just two main runners with a few extra bits to attach suspension and the like to?
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smart51
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| posted on 16/6/06 at 11:58 AM |
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overall vehicle width 1.4m, wheelbase 2.04m. height 1.26m. top speed about 85mph. dual front wishbones, rear trailing arms. mid mounted engine.
400kg unladen, 600kg fully laden. It probably doesn't have to be too strong to cope with the forces that it will be subjected to.
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leto
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| posted on 16/6/06 at 02:31 PM |
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Your description sounds very much like a slightly scaled down Sylva Riot. How about a similar frame?
If you can put figures on how strong “strong enough” is, it will only take some calculations to come up with an answer to you question. The only other
way to give a serious answer is by experience and as your problem is a little specific that experience might be hard to find.
“As light as possible” will mean very small margins on safety and 85 mph sure is enough to kill. Would you really trust an answer from a stranger on
Internet?
[Edited on 06-6-16 by leto]
“I'm gonna ride around in style
I'm gonna drive everybody wild
'Cause I'll have the only one there is a round”. (J. Cash)
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smart51
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| posted on 16/6/06 at 03:29 PM |
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I wouldn't trust a stranger on the internet but I do value peoples opinions; there are some quite knowledgeable people on here.
I like the silva R1ot and I'm sure there is a lot te learn from it. depending on engine choice it may do 150 MPH and with wider tyres may well
carry much higher speeds through corners. It is also intended to handle to race car specifications. My eco car will not have to be as rigid as a
R1ot as the forces acring on it will not be so large.
When I say as light as possible, I mean within the bounds of safety. Ihave included some provision for crash safety. There are some things that
shouldn't be compromised.
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leto
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| posted on 16/6/06 at 05:19 PM |
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I have heard of a design rule that you might have use for:
The cars torsion rigidity in lbs ft/grade should approximately equal the wight (mass) in lbs, for a racer, double the wight.
I trust my source on this one 
“I'm gonna ride around in style
I'm gonna drive everybody wild
'Cause I'll have the only one there is a round”. (J. Cash)
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MikeRJ
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| posted on 21/6/06 at 01:30 PM |
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quote:
Originally posted by smart51
That was 10 years ago when the best you could buy was a Citroen AX at 48.8 MPG (petrol).
In 1989 the 1.4 diesel AX managed to get into the Guiness Book of Records with 112mpg, done on the M11 motorway in the UK
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smart51
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| posted on 21/6/06 at 02:31 PM |
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The AX 1.4 diesel had an official euromix figure of about 75 MPG. I can't think of a better diesel car to date. The C1 or C2 HDi did 69 MPG in
the new style MPG test which is aproximatley 73 MPG in the old test.
The C1 petrol at 61 MPG has the same CO2 emissions as the 69 MPG diesel due to diesel being more dense than petrol.
I want to make a 100 MPG petrol car. I reckon I could probably do it. Maybe.
[Edited on 21-6-2006 by smart51]
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3GEComponents
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| posted on 21/6/06 at 08:24 PM |
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How about this?
 
Rescued attachment hurricane_pro.gif
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Mark Allanson
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| posted on 21/6/06 at 08:51 PM |
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quote:
Originally posted by smart51
The AX 1.4 diesel had an official euromix figure of about 75 MPG. I can't think of a better diesel car to date. The C1 or C2 HDi did 69 MPG in
the new style MPG test which is aproximatley 73 MPG in the old test.
The C1 petrol at 61 MPG has the same CO2 emissions as the 69 MPG diesel due to diesel being more dense than petrol.
I want to make a 100 MPG petrol car. I reckon I could probably do it. Maybe.
[Edited on 21-6-2006 by smart51]
The PSA 1400cc diesel could run for upto 3 months or 2500 miles without the head gasket failing, but after a major revamp/redesign and an increase of
capacity to 1500cc, this was inproved to 12 months or 10,000 miles. Not the most reliable engine that PSA ever produced
If you can keep you head, whilst all others around you are losing theirs, you are not fully aware of the situation
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