I have a hypothetical question. If I were to make a ladder frame chassis for a 400kg microcar, what size steel tubes would be apropriate for the length of the vehicle. 50mm diameter x 1.5mm? 40mm? The less weight, the better.
Why steel? Wood has agruably the highest stiffness per kg of any material barring the exotic.
A ply box structure would be stiff, strong and could incorporate the body panels.
If it were me I would use 3mm birch ply, coat it with epoxy resin (as in boat building practice) and reinforce locally at loadbearing points.
Design could be by "evolution" i.e. design light and when it breaks make it stronger. The West epoxy system makes this easy and cheap to
do
Could use foam in the nose for a deformable structure, bicycle air springs and motorbike brakes.
OOh arr I'm getting quite excited.
Could I get a V8 in it do you think??
Microcar = 400kg ????
Locost can be 400kg without too much effort
A good seven can be 400kg, without doors or roof or window glass. Without niceties like a heater or radio.
Lightweight seven builder often have a good budget for expensive lightweight materials too.
I'm interested in how big a section I might need for the lengths in the chassis given that there will be a single tube along each side.
sounds a bit like a formula 750 racer to me..?
What about an A-frame style chassis? Something like the one used under the liege which has been pretty sucessful in trials and is very
lightweight.
I'd have thought a decent ladder made from 50x50x1.5 mm would be fine for a microcar (which is the basis for 750 racers) Only twice the weight
of 25x25x1.5 but much stiffer (about 8 times is a figure that I've seen but not checked).
Ladder frames really need the larger sections.
... no Ned, not a racer of any formula. A long term design project of mine is to design a car capable of a combined 100 MPG. I used to think it was
easy.
[Edited on 14-6-2006 by smart51]
roadgowing car? depends on the kind of speeds you want it to do, a friend of mine did it with a gokart type car at college, they were racing against
cars with r/c plane engines!!! if you make it a hybrid it shouldnt be that hard, those suzuki carry things with 750 engines do around 75mpg. it also
depends on how you drive
Yes, a road going car, with a 500cc engine. Top speed of 80 or 85 MPH. 0-60 in about 16 seconds.
My current weight estimate is 395kg. The target is 350 but I don't know if I can loose any more weight. If 40mm diameter tubes would be strong
enough, then I'll save a tiny bit.
quote:
Originally posted by smart51
Yes, a road going car, with a 500cc engine. Top speed of 80 or 85 MPH. 0-60 in about 16 seconds.
My current weight estimate is 395kg. The target is 350 but I don't know if I can loose any more weight. If 40mm diameter tubes would be strong enough, then I'll save a tiny bit.
it's EEC-approved so get one and drive savely 
what kind of engine are you using? and have you planned the 100mpg from anywhere, or is it just a guess that you hope to hit? ive just remembered that the suzuki carry 75mpg was a camping one as well, with hightop and kitchen unit etc, so cannot have weighed that little. are you doing a two person one or bigger?
The best engine I've found so far is a 505cc MPI engine made by Lombardini. 24 BHP @5400 RPM. They do a 1000cc diesel which is more powerful and would be quicker but the efficiency is about the same so theres no real advantage.
skinny tyres and slippery shapes will also help that 100 MPG target.
just out of curiousity why are you making this? it sounds like quite a fun project, maybe one for me to try once the 7's finished
My seven is finished. The kit was a kind of trial build. I'm doing it beacuse I was convinced that I could do better than the mainstream
manufacturs. That was 10 years ago when the best you could buy was a Citroen AX at 48.8 MPG (petrol).
145/60/13 tyres, an estimated 0.25 Cd and a frontal area of 1.4m2 are all really good. Reducing them much more would be hard.
So, anyone willing to venture an opinion on the steel? I'm not planning to build unless I can get the theory to suggest something close to 100
MPG. calulations at the moment suggest anything from 60 - 90 MPG (euro combined figure)
For a backbone chassis a single 4 inch tube with 1/8 wall will have about 1000ftlbs per degree stiffness. That's enough for your project.
If you want two tubes then how about two lengths of 4x2-14guage RHS. Two of these will give over 600ftlbs, probably enough if you really are serious
about weight.
The easiest way is to make a light weight Locost!
its very hard to say seeing no design or plan, but id say thats its definately possible, it depends also on how user friendly you want it to be
(luggage space etc), but i do know that designing a car is not easy work, and youd better have some time on your hands to complete it!!
A chip upgrade on a Prius will give you 100mpg (supposedly! 
) - don't know whether that would happen on the combined cycle though. 
btw if light weight is more important than handling and/or safety, then opt for the smallest diameter tube.
[Edited on 15-6-06 by locost_bryan]
quote:
Originally posted by locost_bryanif light weight is more important than handling and/or safety, then opt for the smallest diameter tube
Surely if you wish to better large design teams with all the manufacturers resources you have to think out of the box?
Just rehashing existing conventional construction methods aint going to achieve the results you are hoping for.
Have you considered tension structures? fabric bodies? inflatable bodywork? minimising moving parts? flexible chassis instead of conventional
suspension?
In my humble opinion only innovative ideas will beat the big boys - the tricky bit is sifting the whacky from the innovative
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.
I considered a GRP monocoque but it isn't recycleable. The ladder bit of my ladder frame isn't at floor level but at a similar height to
the top rails on a seven chassis - a consideration for crash worthiness. My chassis design includes colapsible structures, for crash, that don't
intrude into the passenger area. A Polypropelene tub and body panels is as light as you can get, apart from maybe a fabric roof and
"doors". Even Carbon Fibre, made thick enough that you don't knock holes in it, is heavier than PP, though it is has a much higher
tensile strength.
I chose a ladder frame after looking at a seven inspired space frame. After cutting out more tubes than I thought wise, it was still a bit heavy. My
thoughts on a ladder frame is that bigger tubes are stiffer per kg than smaller tubes.
The main reason large car manufacturers don't do micro cars is because they don't want to. They feel safe with proven manufacturing
techniques of steel monocoque structures. If I succede with my design it will not be because I can do better than them but just because I want to do
it.
How much of an issue is recycling with this?
this might give you some ideas
http://www.uniquemotorcompany.co.uk/
the QPods seem to weigh only 220kg
The Qpod has a top speed of 28 MPH and does 60 MPG. It seems to be made of 25mm round tube, which is probably fine at those speeds.
I want something more like a car and with 50% better MPG.
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.
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.
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.
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.
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.
cymtriks, I accept what you say about ladder frames but we're looking for something close to the ultimate to achieve the design goals.
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.
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?
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.
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 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.
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
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).
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]
How about this?
Rescued attachment hurricane_pro.gif
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]
