smart51
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| posted on 14/6/06 at 11:01 AM |
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non seven chassis
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.
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v8kid
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| posted on 14/6/06 at 11:43 AM |
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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??
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Kissy
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| posted on 14/6/06 at 12:24 PM |
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Microcar = 400kg ????
Locost can be 400kg without too much effort
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smart51
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| posted on 14/6/06 at 12:58 PM |
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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.
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ned
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| posted on 14/6/06 at 01:30 PM |
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sounds a bit like a formula 750 racer to me..?
beware, I've got yellow skin
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iank
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| posted on 14/6/06 at 02:07 PM |
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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.
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smart51
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| posted on 14/6/06 at 02:18 PM |
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... 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]
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peterriley2
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| posted on 14/6/06 at 03:19 PM |
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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
Joel
If you dont respect yourself, dont expect respect from anyone else
Live your dreams, dont dream your life
Women only want you for one thing- everything!
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smart51
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| posted on 14/6/06 at 03:26 PM |
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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.
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t.j.
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| posted on 14/6/06 at 04:51 PM |
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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.
 
kart
it's EEC-approved so get one and drive savely 
[Edited on 14/6/06 by t.j.]
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peterriley2
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| posted on 14/6/06 at 05:44 PM |
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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?
Joel
If you dont respect yourself, dont expect respect from anyone else
Live your dreams, dont dream your life
Women only want you for one thing- everything!
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smart51
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| posted on 14/6/06 at 07:18 PM |
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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.
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Volvorsport
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| posted on 14/6/06 at 07:21 PM |
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skinny tyres and slippery shapes will also help that 100 MPG target.
www.dbsmotorsport.co.uk
getting dirty under a bus
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peterriley2
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| posted on 14/6/06 at 07:31 PM |
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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
Joel
If you dont respect yourself, dont expect respect from anyone else
Live your dreams, dont dream your life
Women only want you for one thing- everything!
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smart51
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| posted on 14/6/06 at 07:44 PM |
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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)
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cymtriks
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| posted on 14/6/06 at 08:07 PM |
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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!
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peterriley2
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| posted on 14/6/06 at 08:13 PM |
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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!!
Joel
If you dont respect yourself, dont expect respect from anyone else
Live your dreams, dont dream your life
Women only want you for one thing- everything!
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locost_bryan
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| posted on 15/6/06 at 02:57 AM |
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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]
Bryan Miller
Auckland NZ
Bruce McLaren - "Where's my F1 car?"
John Cooper - "In that rack of tubes, son"
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smart51
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| posted on 15/6/06 at 07:16 AM |
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quote:
Originally posted by locost_bryanif light weight is more important than handling and/or safety, then opt for the smallest diameter
tube
Just because light weight is important, it doesn't mean that safety isn't. The point of good design is to make it strong enough and light
enough.
The Prius will do 65 MPG but if costs £17000. An £x000 battery upgrade will make it do nearer to 80 MPG. I want to beat that for less than half the
price.
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v8kid
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| posted on 15/6/06 at 08:17 AM |
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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
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JonBowden
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| posted on 15/6/06 at 08:49 AM |
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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.
Jon
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smart51
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| posted on 15/6/06 at 10:08 AM |
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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.
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DIY Si
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| posted on 15/6/06 at 10:12 AM |
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How much of an issue is recycling with this?
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JonBowden
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| posted on 15/6/06 at 11:29 AM |
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this might give you some ideas
http://www.uniquemotorcompany.co.uk/
the QPods seem to weigh only 220kg
Jon
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smart51
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| posted on 15/6/06 at 11:45 AM |
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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.
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