Saturday, 22 October 2011

Suspension diagrams

In my venture to learn more about vehicle dynamics, and apply that knowledge to racing simulators, I found the need for some fairly intimate analysis of the cars. The characteristics of the suspension are affected by a lot of things. For instance, in an Endurance Series DBR9, the default front spring rate of 245n/mm translates to a 'wheel rate' of 133n/mm when measured at the wheel. This is due to various factors in the suspension geometry. I figured this would be helpful to understand on a car-by-car basis, so I'm working on a program to draw diagrams of the suspension geometry on these cars. Read on for more info.

If you've studied chassis design, you've probably come across this before. For a start, the force which is exerted onto your suspension by your spring and/or damper is directly proportional to the cosine of the angle between the spring/damper and the direction of travel. And on top of that, there's the effect of leverage to take into account aswell. In fact, theoretically, even body roll can change the wheel rate. But I don't think it's practical to take that into account unless I were trying to simulate the car's behavior.

It's a very straight forward program to use. All you have to do is point it in the direction of a .hdv file, and it produces two PNG graphics showing diagrams of the car's suspension geometry. One for the front, and one for the rear. Here's what the product looks like for the DBR9 in the Endurance Series mod for rFactor.

I should probably have added a white background to these graphics...
The green lines indicate the suspension 'bars' (two in a V shape for a wishbone, etc.), the blue line is the spring+shock absorber, and the red dots represent bodies. Typically the spindle and wheel in each corner. A very crude tire is also drawn, so you can see how the tires compare. Both the width and radius are accurate, however camber is not.

Most of the numbers can be disregarded. The only one you really need to take note of is the last one on each side, as this is the ratio between spring rate and wheel rate. The rest is simply there for 'debugging', to ensure the calculations are working properly. I'll go into more detail about the workings and exact calculations in another post.

Currently, the program is able to parse vehicles in GTR2, rFactor, and Race 07 (assuming they aren't encrypted). Adding support for other G-Motor based games like GTL, GSC, etc. shouldn't be a problem.

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