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Author: Subject: suspension software
Bare

posted on 15/3/11 at 04:00 PM Reply With Quote
suspension software

I'm after some suspension software
I've been fooling with this one: http://www.racingaspirations.com/?p=286
But when I input the suspension dimensions (from Lotus owners manuals) for BOTH a Lotus S3 seven AND a Lotus Europa the resultant numbers are ermm..poor. Triple checking each continues to produces poor result (serious camber change, very high roll centre)
Having owned Both cars and verifying that the S3 suspension design is essentially identical to current Caterham..
I'm having trouble reconciling result with reality. Both cars handled pretty darned well .

I'm wanting to try another program to see what it or I am doing wrong.
Know of any erm.. freebies or 'trials'.

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SeanStone

posted on 15/3/11 at 05:56 PM Reply With Quote
i'm doing a motorsport engineering degree and i havent managed to find any decent trials or 'free' versions of the software we use. you do however have the option of writing yourself a bit matlab script. it'd be pretty complicated and long winded but all the tutorials and information you need are out there and you'd learn a lot about a very powerful bit of software.
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Bare

posted on 15/3/11 at 06:58 PM Reply With Quote
I have subsequently found this one :
http://www.susprog.com/index.htm
It appears as well recieved/recomended..on a couple of racer forums.
But in truth it's looking to be a steep struggle to learn/master/use.
2 steps forward 1 step back.. Sigh.
As for making my own scripts? well... Email was a challenge, unfortunately.

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balidey

posted on 15/3/11 at 07:25 PM Reply With Quote
Ever thought of using the String Computer? Would that give you want you need to work out?





Dutch bears have terrible skin due to their clogged paws

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tilly819

posted on 15/3/11 at 09:59 PM Reply With Quote
String computer +1
tilly





F20C Haynes roadster 440 BHP/Tonne

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Bare

posted on 15/3/11 at 11:10 PM Reply With Quote
Yesss Had thought of that. May yet resort to it.
Did a wee bit of searching and the Initial
http://www.racingaspirations.com/?p=286
Appears to have earned decent respect ..

It's also possible the ancient Lotus suspension ..Was?... less than it could have been :-)

Have found 'OptimumK' as a 2 week trial download.
It's seemingly quite capable, being a widely used University level program.
Not easy to learn though If a luddite :-)

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SeanStone

posted on 16/3/11 at 01:16 AM Reply With Quote
what exactly are you modelling/trying to find out?
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MikeCapon

posted on 16/3/11 at 08:01 AM Reply With Quote
quote:
Originally posted by Bare

Know of any erm.. freebies or 'trials'.


Have a search on tinternet for Greg Locock's Slark which may confirm or deny what the racingaspirations prog gives you....

ETA Done the searching for you. Scroll down to slarck.zip

Linky thing

[Edited on 16/3/11 by MikeCapon]

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40inches

posted on 16/3/11 at 08:29 AM Reply With Quote
I have used V1.1 of this: http://ww.performancetrends.com/listmanager/Feb%202011%20Newsletter.htm
Easy to use and accurate, only a 10 day trial, but you may or may not find a crack on the interweb

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Sam_68

posted on 16/3/11 at 08:31 PM Reply With Quote
Some random observations:

* Yes, 60's Lotus geometry will appear 'poor' by today's standards. It was designed for narrow, high profile tyres that were (comparatively) very tolerant of camber variation. That's why Elans and Europas work best with their original, narrow tyres and one of the reasons why modern Caterhams have much stiffer suspension than the original Lotus Seven, to limit the shortcomings of the suspension when used with modern wide, low-profile tyres. What are you getting for static roll centre height - about 85mm?

* Be wary of most computer geometry software; a lot of programs use flawed calculation methods. One common trick, to make the calculations easier, is to assume that the chassis rotates about a point at ground level (or level with the bottom wishbone chassis pickups) on the centreline of the car, regardless of where the geometric roll centre is located. To do it properly requires horribly complicated maths, and most people just don't bother.

* Even if they do manage to calculate the roll centre geometry accurately, it won't give you a true reflection of the real-life suspension geometry without feeding it a lot of extra data that most computer programs can't cope with....

* At risk of stating the obvious, cars have wheels at both ends, and unless you have a really, really flexible chassis, they can't roll independently, so any computer progrma that analyses only one end of the car at a time is going to give false results from the outset.

* Similarly, cars will almost always have different roll resistances and roll couples front and rear. This means that they do not neatly rotate around a roll axis drawn between the front and rear roll axes like a pig on a spit as you might expect them to. You will get 'skewed roll' where the car leans more heavily on one outside corner, therefore in reality you're effectively getting a combination of roll and squat/dive. The differences to wheel geometry can often be dramatic...

* To get anywhere close to analysing what is actually happening, you need to start by calculating the weight transfer and (using your spring and ARB rates to calculate roll resistances) work out how much each spring will compress, thereby giving you a proper indication of this 'skewed roll'. Of course, to calculate weight transfer accurately, you need to know the geometric roll centre position, which often moves as the car rolls/dives/squats, demanding yet more incredibly fancy maths to chase its tail... which is why thickos like me tend to make a fixed roll centre one of the key parameters of any suspension design, just so you can be sure the little bugger stays in one place while you're trying to do your sums around it!

* ...and then you've got potential additional complications like pneumatic tyres, which compress in sequence with the springs but at a rising rate; or possibly limited droop on the suspension, which means the progression of 'skewed roll' isn't linear as one of the inside corners can go 'solid' as it reaches the limit of its extension (especially if there's any preload on the springs).

In summary, don't believe computer programs: garbage in=garbage out, and it's very difficult to feed them good quality garbage!

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Bare

posted on 17/3/11 at 02:42 AM Reply With Quote
Thank you all for the help..
I'm in process of drawing a Caterham SV Clone. At least it started that way as I could no longer fit into my old S2, if I still had it . I also prefer the visuals of the original Lotus 7 to that of the Champion version(s).

I've located a few Lotus Seven 'plans', all of which were claimed 'accurate' by their proponents.
None actually are ..when redrawn in Autocad, at least, they show their errors early and glaringly.. sigh
My drawings are mostly all done, so I'm 'testing' the front suspension layout as insurance.
I input Genuine dims from an S2 Seven, an Elan, Europa (Not so surprisngly they are not significantly different in geometry from each other or a Lotus 7.(caterham too) main differences are in materials used.
Astonshingly.. all... demonstrated high roll centres and high camber shift with significant steering/toe issues on bump and drop. The steering issue is the most worrying though.

Initial thought was that I was using a crap suspender pgm. How could those Lotii setups not be perfect ?
Apparently it's not ..that.. crappy a pgm... and naivety is to blame?

Yes I've played some with the Spreadsheet, I've had it for some years.. Not enough playing on it yet though.
Thank for, your efforts linking to it, on my behalf.

Sam: the OtimumK pgm...Does.. use all those factors you've carefully outlined plus several additionals you haven't.
Without doubt it IS a 'good one' Substantiated by usage in several University engineering departments.

Now IF only I can learn to plod through it within the 14 day trial ?
Hopefully enough to see if there IS a slightly better setup that I can use, based on the basic Lotus/caterham suspension building blocks

Hey! it's just lines onna Screen.. so far... so anything? is possible :-)

[Edited on 17/3/11 by Bare]

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Sam_68

posted on 17/3/11 at 09:23 AM Reply With Quote
A couple more random thoughts:

* Your comments oin bump steer don't square with my practical experience working on Elans: you can dial most of the bump steer out by careful shimming of the rack height, so might be worth playing around with this on your computer model.

* A good bit of the traditional Lotus 'feel' comes from having a relatively flat roll axis combined with even weight distribution (although the Elise is an exception, due to the height of the engine mass). Unless you're planning to get into tricksy linkages for rear axle (assuming you're cloning the Lotus/Caterham de Dion), then you're stuck with a fairly high roll centre at the back and lowering the front roll centre will diverge from this principle and change the feel of the car.

* High roll centres are not necessarily a massive evil. High roll centres reduce body roll (and/or allow the fitment of lighter ARB's), which would generally be considered a very good thing. Their biggest adverse side effect is jacking, and that's only a real problem at the rear, where it causes Triumph Spitfire style tuck-under oversteer. You can't get tuck-under with a beam axle. A high roll centre at the front will logically give you tuck-under understeer which isn't necessarily such a bad thing and which can in any case can potentially be limited by limiting suspension droop or using the ARB to resist it.

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ettore bugatti

posted on 17/3/11 at 11:17 AM Reply With Quote
Is this usefull?

http://www.superseven.se/Casim/casim_top_page.htm

+data Caterham
http://www.locostbuilders.co.uk/viewthread.php?tid=104805

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Bare

posted on 17/3/11 at 03:54 PM Reply With Quote
Thank you.. all, gentlemen

All information is genuinely appreciated. and suggested programs will be tried.

Yes..I'm well aware of the handling capabilities from the venerable Lotii.
Having owned various of the rascals for over a 20 years period, in the past though.
Also years ago (30?) the wife ran our Lotus Seven S2 to national 'runner up' in Auto X.
So I retain some memories, albeit distant, that the handling was capable and very tunable.
Not arguing that at all.

I only wish to replicate it... but my detailed dimensional informations on the vertical distance between upper and lower suspension arms vary from 7.75", to 8.22" Elan/Europa/ Seven S4 to 8.5" on S2 'plans'.. using the triumph uprights, as am I.

The first is imo 'likely' the more correct dimension as being directly measured from a 2004 Caterham SV.
I would like some reassurance on it though, before committing it to steel.. which led to my current problem.. and confusion when the computer screen gave odd result.

Eupdate:
Ettore :-) The Casim pgm is proving Very interesting/educational.
While not even close to the sophistication of the optimumK pgm
This one is 'old git ' manageable/useable and likely every bit as sophisticated as the calcs/formulas available back when Lotus was designing the Elan and Seven..
more than 'good enough' for my purposes:-)

Thank you.


[Edited on 18/3/11 by Bare]

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Matty Dog

posted on 28/3/11 at 07:52 AM Reply With Quote
Has anyone seen this?
http://sites.google.com/site/porschersk718/step8a%3Adesign
It's a free suspension design programme that was put together by a really clever guy here in New Zealand (have a look at his site for an interesting, if brief, project diary).

Make sure you buy him a beer if you find it of any use!

Matty Dog

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