Modelling camber change in roll etc.

[fastback33]

I tried a search for some general modelling techniques on the site and google, but couldnt come up with much.

I am curious though, as my knowledge goes deeper into vehicle dynamics, I want to start to model the effects of camber change, body roll, and forces acting on the car given a specific steady state input. Then be able to change say my inboard or outboard xyz points on the car. Does anyone have a good starting point for doing something like this? I was thinking along the lines of Multibody systems approach, but the one book I have is more geared towards msc/adams, where i would like to use matlab or some such alternative.

[Jersey Tom]

Purely front view kinematics for a double a-arm suspension is just a 4-bar linkage. If you want to see the effect of moving hard points, you do have to take the multi body / linkage approach.

[PlatinumZealot]

You will need to refresh yourself in vectors and maybe some matrices, fastback.
I started a kinematic model in excel, but then I abandoned it for a simple moveable 3D wireframe in a parametric CAD program such as Solidwoks. The excel file involved too much mathematics, and solidworks was just easier even though it was not made to do this kind of thing. In the little sktech file in solidworks I can track the roll centres when I move the wireframe, which I set up for inputs of roll and ride height. I can change the inputs to individual suspension travel if I want as well.

This is my way of doing it, but there are programs out there like MSC Adams that were built for this kind of stuff.

I found that trying to decide on a Roll center is pretty useless if you don't have a base to start with. The concept is sort of abstract since the location changes all the time and it just a geometrical representation of how much load from the wheels go into the chassis vs the shocks and springs.. and even then it is still an approximation when you have flexible joint and friction between the parts as in real life. Interesting exercise but I wouldn't waste too much time on it.

[Tim.Wright]

First things first, if you are interested in investigating effects of camber change, roll etc then you will need to have at least a basic model of the tyre. If thats a given, then you can worry about how to model the things attached to the tyre.

I agree with the idea of starting in 2D (front view). I have written m-files which solve for the forces in a static case for a double wishbone suspension in front view (2D) and 3D. Its reasonably simple 6 equations /6 unknowns (one for each link force) - smash it all into one big matrix equation and solve for the unknowns. Half of this code I wrote while sitting in a pub. Next step is to write some code to do the kinematics.

Yes, its too much for excel but perfect for matlab or even VB. the next step up is to use the Sim mechanics toolbox for Matlab which lets you make multibody systems in a block diagram format. This will give you a lot of scope for investigation of different suspensions without the massive complexity of learning a full MBS system like adams.

For steady state situations, it is all just a matter of making sure all of your forces and moments = 0, whether its 2D, 3D, Mcpherson or double wishbone.

Tim