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Author: Subject: Ultima chassis improvements
Rod Ends

posted on 5/1/12 at 04:23 PM Reply With Quote
Ultima chassis improvements

Student Dissertation on Ultima chassis stiffness improvements
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snakebelly

posted on 5/1/12 at 06:45 PM Reply With Quote
an interesting read
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matt_gsxr

posted on 5/1/12 at 07:21 PM Reply With Quote
Good amount of work in that MSc.
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Rod Ends

posted on 5/1/12 at 08:48 PM Reply With Quote
Just remembered this - a BMW V12-powered Ultima with lots of improvements including chassis stiffening.
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RK

posted on 6/1/12 at 02:09 AM Reply With Quote
I now know that building a chassis with carbon fibre is very expensive.




But then I already knew that. I won't be sitting any engineering degree exams anytime soon.

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orton1966

posted on 6/1/12 at 06:29 AM Reply With Quote
Two ways of viewing this work

There are two ways of viewing work like this:

The easy way is to sit back and say how obvious the findings are; look at a chassis find rectangle openings and either turn them into triangles or cover the opening with a plate!

But thats not what his work set out to do, like us, he already knew that was the approach to take (possibly he had seen the other Ultima build site, so what!), what he did set out to do was to test this approach via cad modelling and computer testing. Basically to put figures to these modifications.

What I would have liked is to see is a comparison of single diagonal braces against the X bracing that were chosen to see if the additional weight of the X was justified. Also Id have liked to see the standard chassis put on a stress jig to check the correlation of the model, likewise if the modifications were actually done have the modified one likewise tested.

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Paul_C

posted on 6/1/12 at 02:52 PM Reply With Quote
Thankd for the link

Thanks for posting the link which was interesting.

The low cost (Canadian $50) option is LISA Finite Element Technologies from http://www.lisa-fet.com/ that I have played with and can recommend.

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scudderfish

posted on 6/1/12 at 04:28 PM Reply With Quote
Lots of interesting looking software here

http://os.cqu.edu.au/oswinsdvd/doc/engineering.html

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coyoteboy

posted on 6/1/12 at 04:28 PM Reply With Quote
quote:
hat I would have liked is to see is a comparison of single diagonal braces against the X bracing that were chosen to see if the additional weight of the X was justified.


According the chassis design books I've read, the answer is "not really but application specific" - diminishing returns and increasing weight.

[Edited on 6/1/12 by coyoteboy]

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Uphill Racer

posted on 7/1/12 at 12:57 AM Reply With Quote
quote:
Originally posted by coyoteboy
quote:
hat I would have liked is to see is a comparison of single diagonal braces against the X bracing that were chosen to see if the additional weight of the X was justified.


According the chassis design books I've read, the answer is "not really but application specific" - diminishing returns and increasing weight.

[Edited on 6/1/12 by coyoteboy]


When I built my race car "not really but application specific" was important as I was the driver.
Cross bracing the leg area of my single seater was for safety.
There was a crush section utilising the suspension before my legs took a hit and then the driver pod less strong to deform. The idea was to allow the G force to be absorbed at a rate that my body could accept bit like a progressive spring.


[Edited on 7/1/12 by Uphill Racer]

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coyoteboy

posted on 7/1/12 at 01:40 AM Reply With Quote
Indeed, hence the application specific - it doesn't make much difference but should you not wish to compromise in some locations then take it to that extreme. As a general chassis triangulation it's OTT, for a safety cell it may help (or hinder, too stiff and you'll massively increase impact forces on the driver of course).
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kb58

posted on 7/1/12 at 04:01 AM Reply With Quote
Here in the states I remember them doing a 35-mph crash test of a NASCAR racecar. As I recall, the car only got dented in about a foot (and was able to drive away), but the datalogs showed that the driver would have died due to the high deceleration... It's a fine line we walk...

[Edited on 1/7/12 by kb58]





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And the book - http://www.lulu.com/shop/kurt-bilinski/midlana/paperback/product-21330662.html
Kimini - a tube-frame, carbon shell, Honda Prelude VTEC mid-engine Mini: http://www.kimini.com
And its book - http://www.lulu.com/shop/kurt-bilinski/kimini-how-to-design-and-build-a-mid-engine-sports-car-from-scratch/paperback/product-4858803.html

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Ninehigh

posted on 7/1/12 at 05:15 AM Reply With Quote
Really? A Nascar driver would die in pretty much any crash they have? I must have read that wrong...






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wylliezx9r

posted on 7/1/12 at 07:58 AM Reply With Quote
quote:
Originally posted by kb58
Here in the states I remember them doing a 35-mph crash test of a NASCAR racecar. As I recall, the car only got dented in about a foot (and was able to drive away), but the datalogs showed that the driver would have died due to the high deceleration... It's a fine line we walk...

[Edited on 1/7/12 by kb58]


35 mph ? Or 135 mph ?





I spent a lot of money on booze, birds and fast cars. The rest I just squandered.
George Best

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coyoteboy

posted on 7/1/12 at 12:16 PM Reply With Quote
Make the vehicle stiff enough and you're effectively just throwing the occupants at the object you crashed into at the impact speed, ive no idea of figures of stIffness of a nascar in frontal impact though, so can't comment on that.
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Doug68

posted on 8/1/12 at 10:08 AM Reply With Quote
IMHO full finite analysis is a waste of time for a tube chassis, its much faster to use a structural analysis program such as this one (Framework):

http://members.ziggo.nl/wolsink/

Which is what I used myself, this is the type of analysis that done when doing basic analysis of structures such as steel framed buildings or power pylons. Basically the whole PITA step of meshing is skipped as you have members of fixed cross sections going from node to node.

Even in buildings with cast in floors (which as in a similar fashion to sheet metal stiffening a chassis) Structural Engineer often still do not go to full FEA but put in fake elements to act as the equivalent of the sheet body.

On X bracing v other types, the length of a tube in compression will determine how much load it can take before buckling, and theres a square relationship so reduce the length of the tube and the potential load it will take will go up a lot. By X bracing you effectively halve the length of the tube being considered in compression.





Doug. 1TG
Sports Car Builders WA

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Neville Jones

posted on 8/1/12 at 12:53 PM Reply With Quote
quote:
Originally posted by Doug68
IMHO full finite analysis is a waste of time for a tube chassis, its much faster to use a structural analysis program such as this one (Framework):
By X bracing you effectively halve the length of the tube being considered in compression.


Ahh, not quite so Doug. You'd have to 'pin' the cross to get the effect you are suggesting. But what to?

The theory might have it so, in part, but the practice shows that it makes little difference, due to the effects of that welded centre cross area.

Section moment has a greater bearing than most would know.

What the 'X' does do is negate or reduce some of the cyclical compression loads in the cross braces, where a single diagonal would cycle.

Cheers,
Nev.



[Edited on 9/1/12 by Neville Jones]

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onenastyviper

posted on 9/1/12 at 10:26 AM Reply With Quote
quote:
Originally posted by wylliezx9r
quote:
Originally posted by kb58
Here in the states I remember them doing a 35-mph crash test of a NASCAR racecar. As I recall, the car only got dented in about a foot (and was able to drive away), but the datalogs showed that the driver would have died due to the high deceleration... It's a fine line we walk...

[Edited on 1/7/12 by kb58]


35 mph ? Or 135 mph ?


Pre or Post Car-of-Tomorrow/Today?

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