torsional stiffness

[mangelikar]

hi everyone... i wanna know which was the value of torsional stiffness of your chasis design... i wanna do an comparative survey about that...
thanks to all

[exFSAE]

Why? You'll just be comparing yourself to a range between "junk" to "good" with a lot of questionable results.

Better plan - calculate how much chassis stiffness you need (very straightforward), and then design around that.

[MalcolmG]

Originally posted by exFSAE:
Better plan - calculate how much chassis stiffness you need (very straightforward), and then design around that.

Is it really that straightforward? Since it's the desired hub to hub stiffness that you would calculate, then you have to assume values for deflection of all other components between the wheel and the chassis in order to know what chassis stiffness you require. Certainly it's doable but I don't know if I'd call it straightforward. Or am I missing something?

[VFR750R]

I've always felt stiffer is better. Several here will mention weight and I won't ignore its importance, there are diminishing returns; but its easier to work with a heavy boner, then a light noodle.

I think most will find physical stiffness never quite matches up to calculated stiffness either.

[mangelikar]

so i know how calculate chassis stiffness, but i only wanna know which is the common value between all, cuz i've checked some documents and talk about a torsional stiffness around 2000 and 5000 Nm/deg

[VFR750R]

I don't even need to know the numbers to know you will not find a trend. For example a single cylinder carbon chassis will not behave or require the same stiffness as a 4 cylinder spaceframe car. And the rest of the variables are way more important then ultimate frame stiffness anyways.

Some recent competitions have been won with cars that I bet are below average stiffness. It all comes down to systems engineering. How stiff does YOUR car need to be.

Its not how stiff your competition is...

[Yellow Ranger]

look at the roll stiffness of your suspension first- at least make it stiffer than that, then look at how the chassis stiffness affects your suspension...

[exFSAE]

Originally posted by MalcolmG:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by exFSAE:
Better plan - calculate how much chassis stiffness you need (very straightforward), and then design around that.

Is it really that straightforward? Since it's the desired hub to hub stiffness that you would calculate, then you have to assume values for deflection of all other components between the wheel and the chassis in order to know what chassis stiffness you require. Certainly it's doable but I don't know if I'd call it straightforward. Or am I missing something? </div></BLOCKQUOTE>

Good point. Hub to hub stiffness is what is straightforward to get. Still, gets you to the ballpark of an absolute minimum that the chassis would have to be.

[suspended_embedded]

Get in touch with your suspensions guy, see how much he requires the car to be stiff.
Do as much as you can to stiffen it up triangulation etc.
Run it on some software like CATIA and then go on further improvising it.

[JamesWolak]

Cornell did a really good SAE paper on this.

Design, Analysis and Testing of a
Formula SAE Car Chassis

Paper #: 2002-01-3300

It should help answer your questions.

[L B0MB]

Our team was just discussing how we could move to a solid rear axle to save a heap of weight. Then it was suggested to lighten the chassis sufficiently so no springs or dampers are required as the chassis will provide the full wheel travel

http://picasaweb.google.com.au/lewis.kitney/UntitledAlbum#5254236148139750546

[Drew Price]

Lewis,

Make sure you design around Rule 6.1.1, the suspension must at the very least have dampers front and rear.

Best,
Drew

[cjanota]

Ah, the stressed driver chassis. We have been working on that for years. We ran out of drivers.