rodgling
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| posted on 27/8/13 at 10:06 PM |
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quote:
Originally posted by garybee
I'm going to go the other way to everyone else and say...NOT a Ginetta G27
It is absolutely awful. It's so bad that I actually had to cut out the section between the rear suspension turrets and weld in something that I
would be happy to bolt my seat belts to (original was simply not safe). As for the rest of it, one day I will give the car a full roll cage and a
proper transmission tunnel to give it some shred of rigidity.
Interesting, I think the GKD chassis is loosely derived from a Ginetta and it looks pretty over-engineered to me, if anything. Not that I know very
much about chassis design mind.
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britishtrident
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| posted on 27/8/13 at 10:08 PM |
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One of the problems with square tubes is when under torsion you get nasty stress concentrations at corners where the tube meets another tube at
welded joints, however in any decently design space frame this should not be a problem.
[Edited on 27/8/13 by britishtrident]
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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phelpsa
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| posted on 28/8/13 at 12:20 AM |
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quote:
Originally posted by scootz
PS - I found this thread when searching for 'torsional rigidity'.
I see the Quantum Xtreme (of which I have a renewed vested interest in) has a torsional stiffness in excess of 4000nm. What would be the norm for a
typical 7-style spaceframe?
Probably nowhere near that, but why do you need that sort of stiffness?
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MikeRJ
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| posted on 28/8/13 at 07:13 AM |
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quote:
Originally posted by phelpsa
quote:
Originally posted by scootz
PS - I found this thread when searching for 'torsional rigidity'.
I see the Quantum Xtreme (of which I have a renewed vested interest in) has a torsional stiffness in excess of 4000nm. What would be the norm for a
typical 7-style spaceframe?
Probably nowhere near that, but why do you need that sort of stiffness?
To allow the suspension to do it's job.
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mcerd1
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| posted on 28/8/13 at 07:49 AM |
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quote:
Originally posted by MikeRJ
quote:
Originally posted by phelpsa
quote:
Originally posted by scootz
PS - I found this thread when searching for 'torsional rigidity'.
I see the Quantum Xtreme (of which I have a renewed vested interest in) has a torsional stiffness in excess of 4000nm. What would be the norm for a
typical 7-style spaceframe?
Probably nowhere near that, but why do you need that sort of stiffness?
To allow the suspension to do it's job.
or to get on the road down under with a 4cyl engine
(I think its 6000Nm/deg for V8's  )
if you google for folk who have imported to / built cars in Oz you'll see a lot of talk about torsional stiffness
[Edited on 28/8/2013 by mcerd1]
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nick205
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| posted on 28/8/13 at 08:42 AM |
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Without resorting to Google, what sort of torsional stiffness do modern tin tops and their cabriolet versions achieve?
A quick Google suggests a figure of 35,000Nm/degree for the Lamborghini Aventador. Obviously the high end of the scale 
[Edited on 28/8/13 by nick205]
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motorcycle_mayhem
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| posted on 28/8/13 at 11:07 AM |
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The chassis on my series landrover (109) is pretty strong, and that's only 2.5mm box section. There's no round tube on it, just a simple
ladder frame. Really needs the suspension upgrading, with pickup points for wishbones (wishbones will have to be fabricated as well, etc.). With a
good Pinto engine, still the ultimate powerplant after all these decades, should be all you would want.
Tube size and strength:
If the wall thickness of a tube is increased then the ability to support bending loads increases by the same amount. If the wall thickness is doubled
then the ability to support bending loads is also doubled.
If the size of a tube is increased then the ability to support bending loads is increased by the square of the increase in size and the tube stiffness
is improved by the cube of the increase in size. If the diameter of a tube is doubled then the load carrying ability for bending loads is improved
four times and the stiffness under bending loads is increased by eight times.
Due to these effects larger sized tubes with thinner walls are usually better than smaller thick walled tubes of the same overall weight.
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mcerd1
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| posted on 28/8/13 at 12:17 PM |
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quote:
Originally posted by motorcycle_mayhem
Due to these effects larger sized tubes with thinner walls are usually better than smaller thick walled tubes of the same overall weight.
but if you go too thin the tubes can be easily damaged - and a bent/dented tube is not much use to anyone 
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PhillipM
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| posted on 29/8/13 at 03:06 PM |
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quote:
Originally posted by scootz
PS - I found this thread when searching for 'torsional rigidity'.
I see the Quantum Xtreme (of which I have a renewed vested interest in) has a torsional stiffness in excess of 4000nm. What would be the norm for a
typical 7-style spaceframe?
Not sure, but they all seem kinda low, our buggy tested out at well over 36,000nm/degree when it was first built.
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scootz
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| posted on 29/8/13 at 08:32 PM |
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quote:
Originally posted by PhillipM
quote:
Originally posted by scootz
PS - I found this thread when searching for 'torsional rigidity'.
I see the Quantum Xtreme (of which I have a renewed vested interest in) has a torsional stiffness in excess of 4000nm. What would be the norm for a
typical 7-style spaceframe?
Not sure, but they all seem kinda low, our buggy tested out at well over 36,000nm/degree when it was first built.
Was it machined from titanium billet!
It's Evolution Baby!
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PhillipM
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| posted on 29/8/13 at 09:17 PM |
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Titanium isn't very stiff, just fyi
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phelpsa
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| posted on 29/8/13 at 09:45 PM |
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quote:
Originally posted by MikeRJ
quote:
Originally posted by phelpsa
quote:
Originally posted by scootz
PS - I found this thread when searching for 'torsional rigidity'.
I see the Quantum Xtreme (of which I have a renewed vested interest in) has a torsional stiffness in excess of 4000nm. What would be the norm for a
typical 7-style spaceframe?
Probably nowhere near that, but why do you need that sort of stiffness?
To allow the suspension to do it's job.
No you don't. You need a certain level of stiffness to allow weight transfer balance control, but the suspension will work quite nicely with
very little torsional stiffness. I'm just asking the question, what makes you think that that level of stiffness is required? Not saying it
isn't, just asking why!
In reply to the question about modern tin tops, numbers in the region of 10,000Nm/deg are common these days for the chassis, which is very good. This
mostly to reduce NVH though, and all the compliance in suspension bushes means that hub to hub torsional stiffness isn't that brilliant.
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phelpsa
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| posted on 29/8/13 at 09:48 PM |
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quote:
Originally posted by PhillipM
Titanium isn't very stiff, just fyi
Depends how you use it...
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PhillipM
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| posted on 29/8/13 at 10:07 PM |
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With my budget?
About the only place I can use it is in my razor 
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MikeRJ
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| posted on 30/8/13 at 11:38 AM |
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quote:
Originally posted by phelpsa
No you don't. You need a certain level of stiffness to allow weight transfer balance control, but the suspension will work quite nicely with
very little torsional stiffness. I
I strongly disagree. How do you damp the motion where the chassis is twisting rather than springs compressing/extending?
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TheGiantTribble
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| posted on 30/8/13 at 02:40 PM |
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Raises head above the parapit...
You choose your suspension settings to work with how stiff or not your chassis is
In older racing cars, the drivers would 'read' the twisting of the cars as they went round corners.
The tyre pressure and suspension settings/stiffness were all softer so as to work with (or because of) the lack of chassis stiffness.
eg
In a modern formula one car, 50 percent of movement is in the tyres...you need a very stiff chassis to make this work.
In say a 1960's Formula one car, much less stiff chassis in fact almost jelly....lots of suspension movement (and a lot more fun to watch it all
working IMHO)
Drops rapidly back behind shelter.
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Camber Dave
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| posted on 10/9/13 at 08:52 PM |
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Square Vs Round tube
I am building mine with 25mm square main tubes as per the book. So easy to fit floor and sides.
But for the side diagonals I am using 19mm round tube flush with the outer face.
I used 2 diagonals for each 'box' with a tricky joint in the middle.
This gives a bigger weld area into the corners to fully triangulate the sides.
I will just Sikaflex the panels to the round tubes as they will be riveted and glued around their edges.
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Bumble
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 posted on 10/9/13 at 09:58 PM |
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Dutton is the way to go!!!!!!!!!!
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