SLARCK - Short Long Arm Roll Centre Kinematics Spreadsheet 1

[GregLocock]

I have posted a spreadsheet on my website that works out the GRC, camber and track, for an SLA suspension in bounce and roll.

http://www.geocities.com/greglocock/index.html

Go to the downloads page and it is down the bottom. Note that it has not been tested for strange geometries - but so far as I can tell it works, with some caveats that are in the readme. Cheers

Greg Locock

 

[mloew]

Greg,

I am looking forward to checking out your spreadsheet. I wanted to get your opinion on a technical paper I recently read:

The Influence of Suspension Modeling Techniques on Vehicle Simulations
by Roger K. Polston & Jeffrey S. Freeman The University of Iowa

http://www.engr.utk.edu/~freeman/pdfs/roger_ASME.pdf

I think it highlights the difficulties in determining certain properties (like Roll Center Location) based on the method of calculation. I personally feel that it reinforces the necessity to implement a high-level multi-body dynamics tool (i.e. ADAMS, DADS) for doing anything other than a first-order study. Best regards,

Matthew Ian Loew

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[GregLocock]

Great paper - if I'd read that I wouldn't have bothered with the spreadsheet - it is exploring the sort of thing I was interested in.

Note that the simple Kinematic and Compliance measures are reasonably accurate for all 3 simpler models - but that they predict entirely different yaw gains to the full model, once you get into the nonlinear range.

I wish they'd write their papers in English though."Purpose–derived models allow the analyst to parameterize vehicle performance with a minimal number of variables, while multibody models have a direct relationship to physical design of the vehicle."

Try saying that after an evening down the pub. Cheers

Greg Locock

 

[MarkLo]

Hi Greg,

This is the best forum on the web!!
I found this forum when searching for Link-X info.

I downloaded your spreadsheet and look forward to crashing excel with ATV data.

I designed and built a near zero roll ATV with SLA front and rear. On an ATV there are less Engine/Rack/Diff. headaches. I can have absolute zero roll center variation if I want. (vertical center)

I really question the Link-X concept. Have you since researched the crossing control arm design since the forum thread with the designer of Link-X?

Oh and am I the only one who designs the intial arm lengths & pivots in 2D CAD? On that note is there some 2D parametric program that works inside AutoCAD? It would be nice to add motion to 2D parts. We have SolidWorks but it is way too much for simple line developments.

Cheers Mark

 

[GregLocock]

Link-X haven't heard any more, which doesn't mean much. I'm working on 5 different suspension projects at the moment (here's a couple)

http://members.optusnet.com.au/greglocock/motorshow.htm

so I haven't had the inclination to think much about it.

Autocad - Racing by the Numbers or Susprog3D do what you want, or more generally workingmodel2D. If you want to do it for free there's Freecad (if I keep pushing it, someone will end up developing a suspension on it then we can all join in). There's a thread on the alternatives further down. One thing we've found increasingly useful with new geometries is to run a Design Of Experiments on the hardpoint locations very early in the design process. This allows us to optimise ride kinematics very quickly. ADAMS has this built in - it takes a couple of days max to spit out the answers, and even creates a dinky little web page that lets you adjust HP locations, and then tells you the kinematic effect. Very very useful.

let me know how you go with the horrible spreadsheet! Cheers

Greg Locock

 

[MarkLo]

Hi Greg,

You have a sweet job, going to all the motorshows

You designed the pick up with leafs and the rigid link? I guess it prevents wheel hopping and spring wrap? The locking diff is a nice touch, the drag racers & 4x4 guys term is traction bar if it is the same thing...

On my many list of projects is to design traction bars for my Ford F350 crew cab, the extreme wheelbase and 7.3L diesel makes for mega frame twist and wheel hopping.

Getting the length and pivot points appears to be more difficult than any SLA design

Cheers Mark