Dave Pollatsek--Dynamic roll centers?

Hello, Dave, I understand you wrote the physics engine for Viper Racing and Nascar Heat if I remember correctly? Do these or any other sims you (or anyone else for that matter) are aware of use dynamic roll centers and jacking effect due to lateral/longitudinal tire forces? Thanks, Todd Wasson --- Performance Simulations Drag Racing and Top Speed Prediction Software http://PerformanceSimulations.Com

Just helping my deja search :) "J. Todd Wasson" <[email hidden]> wrote in message news:[email hidden]... | Hello, | | Dave, I understand you wrote the physics engine for Viper Racing andNascar | Heat if I remember correctly? Do these or any other sims you (or anyoneelse | for that matter) are aware of use dynamic roll centers and jacking effectdue

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| to lateral/longitudinal tire forces? | | Thanks, | | Todd Wasson | --- | Performance Simulations | Drag Racing and Top Speed Prediction | Software | http://PerformanceSimulations.Com

On 02 Jul 2001 03:58:12 GMT, [email hidden] (J. Todd Wasson) wrote: > Hello, > > Dave, I understand you wrote the physics engine for Viper Racing and Nascar >Heat if I remember correctly? Do these or any other sims you (or anyone else >for that matter) are aware of use dynamic roll centers and jacking effect due >to lateral/longitudinal tire forces? I don't. ;-) Have enough trouble figuring out realistic values for a static roll center already. But it has been said here I think that GPL uses static roll centers. I don't know btw, but as my body rolls, the wheels roll along a bit too, so maybe I could consider that as a sort of jacking effect (as it moves laterally when the body rolls). Ruud van Gaal, GPL Rank +53.25 Pencil art : http://www.marketgraph.nl/gallery/ Free car sim : http://www.marketgraph.nl/gallery/racer/

Can't answer for Dave, but Heat does have settings for front and rear roll centers in its physics files. Cheers, Steve Blankenship "J. Todd Wasson" <[email hidden]> wrote in message news:[email hidden]... > Hello, > > Dave, I understand you wrote the physics engine for Viper Racing andNascar > Heat if I remember correctly? Do these or any other sims you (or anyoneelse > for that matter) are aware of use dynamic roll centers and jacking effectdue

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> to lateral/longitudinal tire forces? > > Thanks, > > Todd Wasson > --- > Performance Simulations > Drag Racing and Top Speed Prediction > Software > http://PerformanceSimulations.Com

>Can't answer for Dave, but Heat does have settings for front and rear roll >centers in its physics files. > >Cheers, > >Steve Blankenship Thanks. They're probably stuck in one spot then throughout the race. Todd Wasson --- Performance Simulations Drag Racing and Top Speed Prediction Software http://PerformanceSimulations.Com

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> >I don't. ;-) >Have enough trouble figuring out realistic values for a static roll >center already. But it has been said here I think that GPL uses static >roll centers. > >I don't know btw, but as my body rolls, the wheels roll along a bit >too, so maybe I could consider that as a sort of jacking effect (as it >moves laterally when the body rolls). > >

Yes, I recall that here about GPL as well. The jacking effect you're talking about here should be a seperate force. If I remember right, you were multiplying lateral force by the distance from the roll axis to the sprung center of mass to get torque and wind up with load transfer. This is only partially correct though, so check into it when you get a chance. The weight transfer will not be correct if this is all that's done. The part you were calculating gives the torque on the body, which eventually causes weight transfer due to spring compression, however, the remainder of the weight transfer is reacted directly through the linkages. This will make a big difference in your sim because you're handling load sensitivity in your tire model. From messing around on paper, I figured that the jacking force exactly equals the load transfer sent through the suspension linkages, but also lifts up the center of mass. This is convenient, because you kill two birds with one stone. I thought they would be seperate somehow, but they don't appear to be. Anyway, I got a good chunk of my double wishbone system working yesterday. The track width and camber change with wheel travel correctly as hoped, so now I can move onto roll center calculations on the fly :-) Was hoping I might be among the first to do it outside of the high priced engineering package area (I think Gregor's been doing it awhile, and I'm pretty sure Chris does it.) :-) Todd Wasson --- Performance Simulations Drag Racing and Top Speed Prediction Software http://PerformanceSimulations.Com