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Virtual Geekdom

Jay Chen
Jul 6, 2007
0707_sccp_1_z+editorial+jay_chen Photo 1/3   |   Virtual Geekdom

Successful racers often say that a good driver is one that drives by vision, not by feel. The rationale is that photons travel much faster to your eyes than the nerve impulses from your ass, so you're able to see yourself getting into trouble well before you feel it. While there's no replacement for real seat time, a passenger can learn a lot about the limits of a car by merely getting a visual impression of its corner entry speeds and braking points. This means there may still be hope for all the reset-button racers out there, assuming the driving games they play are realistic enough.

If you haven't realized it by now, this month's column is nothing but a geek's version of a game review. So flip the page lest you get sucked in and converted as I did. Last month, I had to put on a different hat. SCC's publisher shipped me off around the country as a racing game consultant. I was only willing to go so I could point out to a bunch of programming nerds how much crack they were smoking. Not the case. Apparently, the people at Microsoft have gotten smart and decided to hire physicists, nuclear engineers, and professional racers like Le Mans driver Gunnar Jeannette to develop their next-generation racing simulation. Furthermore, the parking lots at these places are filled with so many fanatically tuned machines driven by gas-guzzling car nuts that it makes our lot look like some teenybopper car meet in front of the local 7-Eleven.

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The reality is that games nowadays aren't that far off from vehicle dynamics simulations or accident recreation programs used by engineers and car manufacturers. It all boils down to proper modeling and adhering to Newton's little laws. Pretty easy when you're modeling some rigid box on a ramp, not so easy when it's a mass of thousands of parts with distinctly different properties. In the case of Microsoft's Forza 2, probably the most realistic game I've experienced, each of the 300 cars modeled are assigned roughly 9000 parameters, all of which are used by the physics engine to compute the cars' responses in real time. Even as an engineer, I have a hard time thinking up a quarter as many attributes to set apart one virtual car from another. Each car has its basic dimensional aspects modeled, like weight, distribution and wheelbase. From that, you can figure out the center of gravity, rotation, rotational inertia, and polar moment of inertia for the car as a whole. Then you have wheel and driveline inertia, which all figures into the power profile of each drivetrain-not to mention the minutiae of suspension motion details.

Developers can't go and measure camber and toe curves for 300 cars, but they do go to the extent of implementing appropriate suspension responses for different types of suspension, whether solid rear axle, double A-arms, multi-link, MacPherson strut or whatever else is left. Race cars also get distinctly different suspension response than production cars. And when you change a car's set-up, wheel rates, roll rates, dive rates, and maybe even interest rates must be recalculated. A linearized model is also used to account for chassis stiffness in various modes.

In conjunction with the physics model is the visual model, which, unfortunately for the developers, is built by hand-virtually. No fancy push-button laser digitizers like you see in the movies. Each car is created using pictures and existing resources for visual accuracy, which are then used to account for a simplified aerodynamic model.

What most games have lacked until now is a proper tire dynamics model, even though it's the most critical element in a game, since it's the only point in which a car interacts with the road. Why? Because rubber is not just an odd and dynamic material in the real world.

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The fact that it doesn't behave like metal or plastic means you can't just assign a stiffness factor to it like you can a spring or chassis. Rubber will stretch, spring back, or at times become slippery depending on how it's stressed. Add varying thermal and pressure characteristics on top of the friction and sidewall characteristics, and you have a complicated physics model by itself.

The physicists behind Forza 2 developed a simplified and computationally tolerable model that integrates all these factors and spits out reasonably realistic tire feel (minus steering feedback and degrees of understeer) using a load-sensitive non-Newtonian algorithm.

Funny thing is, add all this up and you still don't come close to 9000 parameters.

Track simulation and modeling underwent the same amount of detail in terms of mapping, texturing, approximating friction and visual references. The digital tracks also have five different friction coefficients for the asphalt: on the racing line or off, bouncing on the rumble strips, or anywhere else you can make a car wander.

Impressive and as geek-stimulating as this is, the real test is obviously from behind the wheel of the three-screen simulator at the Forza development office. I was still skeptical and frustrated with the steering and non-hydraulic brake pedal dynamics. That's to be expected when you replace mechanical parts with potentiometers. What I didn't realize until much later was that, behind the wheel, I was employing all the driver training and reflexes we use on track from the get-go: smooth inputs, looking into turns and past the apex, finding the sweet line that doesn't upset the car. You can even see the car yawing if you brake too aggressively for a turn with one set of tires on the slippery tiger stripes and the other tires on the grippy line. It's a bit disorienting when the only thing missing is the gs. On familiar tracks, braking points, turning points, visual markers and quirky terrain changes are all exactly where they've been burned into my memory from the real thing and cued only by visual inputs. Any more and you're overcooking a corner. Any less and you're going slow and sucking.

I'm really contemplating selling Project Corolla for the three-screen, three-Xbox 360 set-up. It's probably cheaper in the long run and will definitely entail fewer grease-filled late nights. And it might just save me from being smoked on a track one day by some 16-year-old newbie with more virtual track time than I have real.

By Jay Chen
85 Articles

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