Gazr81
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| posted on 23/2/04 at 08:00 PM |
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First time and having a go
Hi all, just found this web site to day while try to do so research while I was meant to be working, I am mad about all things cars like most of you
seem to be here so I guess I am in the right place, I am in the process off finishing a vtec powered mini and have caught the car building bug big
time and want to take a leap in to the deep end and build my own design of car from scratch, I am a computer engineer by trade but cars are my first
love, I download rhino’s 3d/cam demo and off ive gone, I am just looking for constructive criticism to what you think of my first attempt at
designing my first very own chassis its a mid mount layout design drawn to 1/10 scale to house a Chevy small block mated to a porche g50 box, please
feel free to comment.
 
Rescued attachment chassis1.jpg
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flak monkey
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| posted on 23/2/04 at 08:04 PM |
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Looking v. nice  certainly using heavy tubing by the looks of it! What size is it?
IMHO could probably do with more triangulation down the sides, just a singe brace across each 4 sided area will make the chassis much stiffer.
People may disagree though....
[Edited on 23/2/04 by flak monkey]
Sera
http://www.motosera.com
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Gazr81
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| posted on 23/2/04 at 08:16 PM |
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Like so should that be better
 
Rescued attachment chassisextra.jpg
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Gazr81
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| posted on 23/2/04 at 08:52 PM |
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The tubing i want to use would be 38mm by 1.5 mm thats what ultima uses so its good enought for me its lookings bigger on the drawing because i
slipped up, on the pic the tube is 2 inches oops
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Gazr81
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| posted on 23/2/04 at 09:03 PM |
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Very nice, weight is not the most important thing the strenght of the chassis to me will me, with the chevy setup i want to run with be pumping out
450 ft/lbs and bhp the chassis needs to be tought, was ive read that round tubes are much stronger to size and wieght compared to tubing thats what
ive gone for, reguarding cutting the tudes to mate up with the other sections i all ready have a fish mouth cutting tool for the job
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flak monkey
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| posted on 23/2/04 at 09:57 PM |
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Ok there are a probably a few more bits i have missed and i have only done one side, but this is the general jist of what i mean . Feel free to tell
me to pi55 off though and ignore me 
Good luck with your dream machine!
Cheers
 
Rescued attachment like this.jpg
Sera
http://www.motosera.com
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JoelP
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| posted on 23/2/04 at 10:22 PM |
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i was gonna point out the rear suspension pickups! Plus, the engine bay could use some horizontal traingulation, though i appreciate this is nearly
impossible without having the drivetrain to work around.
consider welded panels on the sides, i suspect it would compare favourably with braces for stiffening.
nice try, doesnt look like a first attempt though! was it computer engineer or mechanical engineer you said?!
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Gazr81
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| posted on 23/2/04 at 10:25 PM |
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Heres some more improvements i cant have the long down bars running down from the top of the frame because on the layout of the body work
 
Rescued attachment back supen.jpg
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Bob C
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| posted on 23/2/04 at 10:28 PM |
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You should read the chassis notes by a member of this forum called cymtriks there's a link to his analysis here - www.locost7.com look in the
FEA section. This guy's work has a ring of authority about it.
triangles are the key to spaceframes. I think the round vs square tube thing is overblown - round tubes are intrinsically stronger in torsion (but
this does NOT equate to significant extra torsional stiffness in a spaceframe) square tubes make stronger beams & are easier to rivet sheets to
and easier to joint - so most folk use square. They're the same in compression/tension which is how they're loaded in a spaceframe.
BIG job you've given yourself there; years of fun!
Bob C
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Gazr81
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| posted on 23/2/04 at 10:32 PM |
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Thanks alot for all the help its much appreciated theres probably going to me many more questions to come.
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suparuss
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| posted on 23/2/04 at 10:45 PM |
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i take it the front is the end with the a-arm suspension? if so, the cockpit looks a tad long, the window suround seems to be directly above the font
bulk head where the pedals would appear to be going. it either is very weird or i dont understand the layout fully. also, you seem to have a lot of
tubes ending in the middle of other tubes where you could quite easily group them together into the same joint. round tube has a better strength in
compression and tension but is significantly weaker in bending than square tube so this ought to be avoided.
and triangualtion is the way to happiness!
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Gazr81
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| posted on 23/2/04 at 11:37 PM |
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I no im a pain but with a bit on reworking i thinks im going down the right lines now (i think) :-0
 
Rescued attachment reartrifount.jpg
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flak monkey
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| posted on 23/2/04 at 11:49 PM |
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Its looking very good but very complex! 
I disagree with Suparuss though about round and square tubes. If anything round tube is WEAKER in compression and tension than the equivalent sized
square tube.
Say comparing 50mm RHS (2mm thick) and 50mm tube (2mm thick). The square tube has more cross sectional area (add it up if you dont believe me - thats
why it is heavier per unit length) so;
extension = (Force x length)/(cross sectional area x youngs modulus)
(Youngs modulus is constant  ) So with the same force the square tube will deform less than the round tube.
Round is better in torsion, but there is little of this in a space fram chassis. But square resists compression/tension better
Square wins for me
Lecture over...can all tell me where to go now
Cheers
[Edited on 23/2/04 by flak monkey]
[Edited on 23/2/04 by flak monkey]
[Edited on 24/2/04 by flak monkey]
Sera
http://www.motosera.com
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Alan B
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| posted on 24/2/04 at 03:00 AM |
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quote:
Originally posted by flak monkey
....... If anything round tube is WEAKER in compression and tension than the equivalent sized square tube........
True...as you say it is proportional to cross sectional area....however true compression failure is rare...buckling is more likely and round scores
well in buckling...look at cast iron columns in old mills....usually round..
quote:
round is better in torsion, but there is little of this in a space fram chassis. But square resists twisting better
Eh?...that's contradictory...good in torsion means resistant to twisting....
or did I misunderstand your point?
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flak monkey
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| posted on 24/2/04 at 09:22 AM |
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Sorry was a typo :-S and still with 2 edits i didnt spot it... sorry
Cheers
Sera
http://www.motosera.com
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Mix
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| posted on 24/2/04 at 09:24 AM |
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Taking the discussion a stage further,
If you were to consider the merits of round and square section material of similar cross sectional area, (ie in the previous example if the gauge of
the round section was increased or it's diameter increased) and therfore equal weight per unit length, what would be the outcome?
At least this way we would be comparing like with like.
Mick
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flak monkey
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| posted on 24/2/04 at 10:08 AM |
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This all comes down to second moments of area, the bending moment in the 'beam' (tube) and the stress in the tube.
The second moment of area of RHS assuming it is square is;
Ia = [(length of 1 side in m ^4)/12] - [(internal measurement in m^4)/12]
For a piece of 25mm RHS with wall thickness of 1.6mm this would be = 1.373x10^-8m^4 [The cross sectional area would be - 0.00015m^2]
A round tube with similar cross section would be 25mm with a wall thickness of 2.08mm.
The secomd moment of area of a peice of tube is;
(pi/4) x (O.D^4 - I.D^4)
For the round tube described above Ia = 1.59x10^-7m^4
The general beam equation is;
(Bending moment/Ia) = (stress at distance y from neutral axis/distance from the neutral axis)
And i bet that doesnt make any sense what so ever!
Cheers
Edit: both tubes will now behave the same in compression, but will still act differently in bending/torsion
Edit 2!!: Right checked, HIGHER second moment of area means MORE resistance to bending (look at I girders). So ROUND TUBE IS BETTER FOR YOUR
CHASSIS, it resists bending more than square tube. Sorry for the confusion!!! I will shut up now
[Edited on 24/2/04 by flak monkey]
[Edited on 24/2/04 by flak monkey]
Sera
http://www.motosera.com
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Gazr81
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| posted on 24/2/04 at 10:30 AM |
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Here are some more modifcation do to my chassis as recomened. thanks agian for all the help.
 
Rescued attachment chassis24th.jpg
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DaveFJ
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| posted on 24/2/04 at 12:20 PM |
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looking good ---- but
you seem to have lost a bit of the triangulation that was present on earlier models
specifically i notice that the front suspension 'box' only has one face braced. I would have thought that this was an area where stiffness
was essential so this should be fully braced in all planes...
Dave
"In Support of Help the Heroes" - Always
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Spyderman
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| posted on 24/2/04 at 02:05 PM |
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Flak Monkey and others,
Comparing sizes and tube/RHS is all very good, but can we keep it relevant.
Gazr81 has said he is planning on using 38mm (1 1/2 inch) by 1.5mm tube.
If you have to do comparisons then try to use the sizes that are being planned. This makes it easier to use and work out the problems.
If there are no equivalent square/round tube then the comparison is pointless.
It annoys me no end when people start comparing material strengths that are not relevant to the thread!
(Rant over)
Terry
[Edited on 24/2/04 by Spyderman]
Spyderman
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flak monkey
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 posted on 24/2/04 at 02:37 PM |
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Sorry, was using the tube sizes as guide lines to clarify a point. And they make my calculations easier!
The same points will apply to whatever sized tubing is used.
If the cross sectional area is the same, then square resists bending better than round.
If the wall thicknesses are the same then square resists compression/tension better than round.
In all cases round is better in torsion than square!
Thank you for your comments spyderman, but like i say i was only giving examples.
David
Sera
http://www.motosera.com
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Alan B
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| posted on 24/2/04 at 03:21 PM |
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quote:
Originally posted by Spyderman
........It annoys me no end when people start comparing material strengths that are not relevant to the thread!
(Rant over)
Terry
Bugger off......
You are right of course.....
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Mix
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| posted on 24/2/04 at 04:32 PM |
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Flak Monkey
Thanks for taking the time to try to educate me
Must admit I understood your last post a lot easier.
Spyderman
Sorry if I caused you stress but I thought that the whole point of this forum was the free exchange of information amongst like minded individuals.
Discussions will always diversify with time, where should we draw the line ?
Mick
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flak monkey
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| posted on 24/2/04 at 04:35 PM |
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Not a problem mate, gave me something to take my mind off the stupid amount of work i have to do!
I hope they clarify some points without being too specific or irrelevant.
Cheers
David
Sera
http://www.motosera.com
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Spyderman
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| posted on 24/2/04 at 05:06 PM |
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quote:
Originally posted by Mix
Spyderman
Sorry if I caused you stress but I thought that the whole point of this forum was the free exchange of information amongst like minded individuals.
Discussions will always diversify with time, where should we draw the line ?
Mick
Try to remember us poor fools that are not as smart as you!
With so many Experts competing their excellence on here now it is very difficult for us idiots to decipher what you are talking about!
Diversification is always a good thing as long as it is of benefit!
Terry
Spyderman
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