Suspension parameters

Hi

Is it possible to output motion ratio, suspension frequency and critical damping ratio in an app?

Or is that information on the vehicles in the sim available anywhere - for tuning the suspension.


Thanks

Mike

 

Critical damping is just the damping required on a spring to allow it to oscillate only once. Surely that's not too difficult to derive from the simulator engine - given they do have springs and the dampers on the set up screen and the rates for them, it should be simple to provide the motion ratio (which is just the ratio between spring movement and wheel movement).

The motion ratio has nothing to do with mass points, it just depends on the angle of the suspension spring vs the angle of the wheel - i.e. when once moves how much does the other.

For a given spring rate, and mass it should be possible to work out the critical damping ratio.

What I mean is that a strong spring under a heavy lorry is actually very soft and has a low natural frequency (i..e it will oscillate slowly). Whereras if you put that same spring under a small light weight car, it would be very fast, and high frequency. Therefore spring rates are useless, it is necessary to know the parameters of the structure the spring is in (i.e. what is the mass attached to it). You need to know the overall frequency of the suspension to balance the car (in terms of oversteer / understeer) - the spring rate by itself is meaningless. They have the numbers, its just a matter of outputting them.

 

That's interesting.

If they are not defined then how does the physics engine process user suspension adjustments. Where for example we specifically input the relevant spring and damper rates to be adjusted?

When I change the anti roll bar rate from what you are saying the model (1) does not know where the anti roll bar is, (2) does not know its geometric alignment (i.e. its angle compared to the wheels) and (3) cannot calculate the distance the wheels will move up when compressed by the ground force (gravity etc).

I am assuming you are an expert from the way you have conclusively addressed the subject. So many thanks for your help.

I was trying to use the sim to understand car suspension better. And how changing the spring rate affects the wheel's response to bumps in the road surface. As you say the physics engine cannot do any of the above.

 

This is how that works: http://wiki.beamng.com/Variables

 

This is done simply by changing the attributes of various beams. Because of the way suspensions are simulated, things like dampening and frequency are usually not able to be accurately simulated as well.

 

Suspension frequency can be measured in game. I once made a script that detected how often a beam length changes direction. With dampers removed at one end of the car at a time, it gave a rough value for suspension frequency. It would be hard to make it work on all cars without modifications, otherwise it would make a useful app.

 

Thanks everyone for the helpful answers. I can see it wouldn't be straight forward to make such an app. However I do think the suspension is simulated pretty well (graphically at least the effect of changing damper settings seems pretty realistic).