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optimizing vehicle physics

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hi there, I'm currently trying to add vehicle physics to our game FragFist. We are using the Nogredex binding of Novodex for ogre. Currently I have quite a few problems. The car's acceleration is too slow and adding horsepower to the engine simply makes the tires slip when accelerating. I have modeled the tires as spheres with joint motors applied to them. Is there any better way to do this? Has anybody here ever successfuly written a driving simulation? Any tips? I'm asking this because all of the hobbyist driving games I have seen so far lack realism in many ways. I'm wondering how popular driving games like "Need for speed" or "Gran Tourismo" handle their vehicle physics. Do they use existing physics engines or is their approach nothing but a big hack? Thanks in advance, Stephan

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Creating realistic driving physics is very hard primarily due to the difficulties associated with tire modeling.

See Brian Beckman's The Physics of Racing, www.Racer.nl, and perhaps obtain a copy of Race Car Vehicle Dynamics. Brian Beckman helped with the driving model for Forza Motorsport on Xbox, which has a more realistic driving model than Gran Turismo 4. You can also find many papers on tire modeling via google.

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I don't know how Novodex handles tire modeling but if you're using spheres for tires, wouldn't the point of ground contact only be at dead-center of the tire rather than the true width of the tire? If so, it would explain why your tires are slipping.

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back in my old university days we did quite a lot of vehicle modelling. One of the most important aspects was that the tire itself have a spring-like nature (not infinitely stiff). A good rule of thumb was that the tire spring be approx. 10X more stiff than the suspension spring. So I guess I could have just said make sure you are modelling the tire as a spring...sorry.

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I dont know how the particular engine you're using works, but the obvious answer is to increase the friction, traction, whatever, between your sphere objects and the ground.

A true vehicle model is rather...complicated. You'll have to deal with slip angles, ratios, and...other ugly things.

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The answer I got from the Novodex support about the subject of making realistic car physics with a generic physic engine was: Don't, use raycast car. I must say, it makes a lot of sense...

(edit) I'll just elaborate a bit more... :) That's what I tried with Novodex:

A realistic car built with joints, sphere for the wheel, approximatively correct masses (except for the wheel block has the system would get very unstable if the mass ratio was too big).

About the traction:

- Spinning the wheel with a motor: no speed at all, whatever I tried and even with anisotropic friction a lot of problems on non trivial road (ie. anything but a plane would cause very bad jumps, skid or whatever at polygon edge boundaries).

- Pushing on the car with impulse/force/whatever :) a lot of work to keep the car on the road, ie. not getting airborne on the slightest bump on the road. Even worse skidding and frictions problems. But that was to be expected since there was no speed limit problem anymore.

About the suspension (sorry if it's not the correct term):

Pretty nasty to get them to feel 'right' and once that was done the car body would never go to sleep. Well it would go to sleep then immediatly wake up and fall down due to gravity, springs would push it back to the correct position (slowly), the body falls asleep then wake up, etc, etc...

My feeling is that car physics are too specialized to be accurately simulated using a generic physic engine and especially one geared toward game physics.

[Edited by - b34r on May 29, 2005 1:38:48 AM]

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