I know the chassis was professionally designed and welded by a certified welder, but the curved tubes are used for cosmetic reasons, and basic principles are usually correct!
I was always taught, and every book tells you, that chassis frames should be made of straight tubes as a curved tube is already bending. I think this
crash would confirm it as there is very little damage to the wall and the frame has folded with the curve and the damage has entered the leg area.
I know the chassis was professionally designed and welded by a certified welder, but the curved tubes are used for cosmetic reasons, and basic
principles are usually correct!
That looks more like a concrete plant trough than a wall and the car has ridden up over it. To have lost it like that would suggest he was probably going a bit faster than advisable but unless you know all the circumstances it is impossible to speculate. Personally I don't think a straight tube chassis made from 1" square 16g would have faired any better.
No expert, but you could use straight tubes for the passenger./driver area probably including a roll bar ect, then curved tubes to allow crumpling
else were and not in the passenger/driver area.. But I supose you should also think about where the engine may end up...
Dan
Hi
Was the driver and passenger OK?
I had wondered too about the wisdom of the Atom having curved main chassis tubes. Goes against good racing car and aircraft design principles for
steel tube spaceframes, such as using straight tubes wherever possible as well as to triangulate and don't put loads in the middle of straight
tubes, or ones already bent! Staniforth's book on race and rally car construction is good for this info, as well as Darrell Stinton and the
EAA's aircraft design books.
The Atom chassis reminded me of Cooper single seater racing cars which had curved tubes that were large diameter and gauge, before others - such as
Lotus - came along with lighter stiffer chassis with straighter, smaller diameter tubes and more triangulation (see:
http://www.500race.org/Marques/Cooper.htm)
This was perhaps one of the reasons that Atom chose such large diameter tubes for the main longitudinal chassis members (and of what gauge?), as well
as perhaps giving an assurance in styling terms to buyers who don't think about spaceframe structures. I note that the Atom chassis has more
traingulation than a Cooper.
Mike
Firstly, I'd like to say that I hope nobody was seriously injured in this Atom.
Unless you've designed your chassis using FEA techniques or done some crash testing then it is likely that any amateur designed Locost will have
weaknesses which will show up under extreme (crash) stress. Probably the simplest type of crash to predict is a head on into a solid structure and
even here you are likely to see some lightly loaded tubes punching through other tubes and perhaps welds failing etc. On the upside, a typical Locost
has the engine in the front and the driver/passenger are quite far back in the chassis so there is not much mass behind which might crush the tubes
around the cockpit.
When building my chassis I was thinking to myself, "This thing will be mega-strong in the event of a collision", but to be honest, having
seen some bent Locosts since then, I'm not so sure... I think mine will be stronger than most because I employed some of Cymtriks's
structural mods and I have used 2mm tubing instead of 1.6mm (due to availability more than anything) but I'd still rather keep the car between
the hedges because it is very unpredictable what might happen in a crash. In some cases having too much strength in the wrong parts of the car can be
as bad as having too little strength.
Stay safe people! 
[Edited on 10/5/2011 by craig1410]
If you crash hard enough it doesn't matter what you're in, you're gpoing to get hurt (or killed).
If you look at the Atom the curved tubes on the side ar pretty pretty big, which probably compensates for the fact that they are curved, if they were
that size and straight though it would be even stronger.
Just plug some numbers into Euler buckling equations for slender struts subject to compressive loads --- the numbers that come out will show
even a very slight curvature greatly reduces the load to failure in compression.
.
quote:
Originally posted by craig1410
......Unless you've designed your chassis using CFD techniques
quote:
Originally posted by Alan B
quote:
Originally posted by craig1410
......Unless you've designed your chassis using CFD techniques
I'm puzzled by this bit...
I thought CFD was computational fluid dynamics which was for modelling fluid flow, areodynamics etc....is there some new or different meaning for CFD related to structural design that I'm not aware of?
Alan
quote:
Originally posted by britishtrident
Just plug some numbers into Euler buckling equations for slender struts subject to compressive loads --- the numbers that come out will show even a very slight curvature greatly reduces the load to failure in compression.
.
i'm sure curved tubes are supposed to be stronger. forget cars, but think about an egg, if you try to press down on the top and bottom with your
fingers, they're near impossible to break, if eggs were cubes it would be very different.
thats how i see it anyway, but i'm no chassis designer
I have no idea about these things, but so far, Blake is making the most sense!
We should be driving egg-shaped cars!
quote:
Originally posted by blakep82
i'm sure curved tubes are supposed to be stronger. forget cars, but think about an egg, if you try to press down on the top and bottom with your fingers, they're near impossible to break, if eggs were cubes it would be very different.
thats how i see it anyway, but i'm no chassis designer
Something like this...
Or this...
^ tasty AND practical 
thats true craig, hadn't thought of it like that
with any chassis though theres going to be curves in it. whether it be one rolled tube, or 2 tubes welded at an angle, like on a 7 chassis at the back
of the engine compartment. hit that slightly off centre, won't that still do the same? it all depends really on whats inside the outside
supporting it
I think I agree with Craig now... Blake - you're a fanny!
quote:
Originally posted by blakep82
^ tasty AND practical
thats true craig, hadn't thought of it like that
with any chassis though theres going to be curves in it. whether it be one rolled tube, or 2 tubes welded at an angle, like on a 7 chassis at the back of the engine compartment. hit that slightly off centre, won't that still do the same? it all depends really on whats inside the outside supporting it
quote:
Originally posted by scootz
I think I agree with Craig now... Blake - you're a fanny!
... imagine thinking that egg-cars were the way forward!
Blake your reasoning applies to round tube vs square tube (i.e. round tube better resists buckling), but not to the use of curved members in
tension/compression i.e. in a chassis. As has been pointed out using curved members in that way dramatically reduces their resistance to buckling. Or,
to paraphrase a certain Mr Chapman: curved tubes are pre-failed
I remember that photo from a good while ago. If I recall, the car went straight on at a t-junction apparently due to a stuck throttle (or was it a
prod of the wrong pedal?). Can't remember any other details, particularly regarding the survival or not of the driver, unfortunately.
As for the Atom's chassis, whilst curved tubes may not be optimum from a pure engineering point of view, if they are over-engineered enough it
really doesn't matter. In other words you can design a chassis to a certain strength using curved tubes by all means, it just wont be as
light/stiff as it could have been with straight tubes. I dare say the Atom chassis is well designed and fit for purpose. Remember also that some
deformation in a crash would likely be designed in, and maybe the curved tubes are part of the mechanism that achieves that in the Atom design? Also,
I believe that was a particularly high speed crash - any tubes will deform if the crash is fast enough.
I remember reading the thread on this, it was posted by his friend, he survived but had severe leg injuries, that was the last I heard
Cheers
David
quote:
Originally posted by Minicooper
I remember reading the thread on this, it was posted by his friend, he survived but had severe leg injuries, that was the last I heard
Cheers
David
At least the brickwork remained unscathed .. seemingly unmarked as well ;-)
C'mon these cars (all of them) are 'safer' than a Moto.... but not a helluva lot safer, clearly, they also require as much skill to
operate.
No one should be surprised at the results of a head on into a genuinely solid object. Happily it wasn't a fatal crash.