Am Freitag, den 30.11.2007, 23:04 -0600 schrieb Curtis Olson: > On Nov 30, 2007 10:11 PM, Jon S. Berndt <> wrote: > Some of the engineering sims I use at work (space shuttle) > have very > > detailed models of landing gear and tire spinup, etc. Of > course, we don't > ever see power trains driving the wheels (at least we don't in > JSBSim). > There are some simplifications made in our gear model that > suffice for > modeling what planes do. However, out of curiosity, I am > interested to see > how ground reactions are modeled for autos - particularly for > the case when > the vehicle is at rest. > > I am familiar with Pacejka's magic formula, etc. It can be a > complicated > problem, so it's useful and interesting to see how others > approach the > problem. > > I think it's worth pointing out that in FlightGear cvs we have models > of a jeep and of a snowplow (truck). The dynamics are based on YAsim > and the wheel/suspension modeling seems to work really well. I was > actually very impressed at the sorts of things that YAsim does ... > Andy cooked a little bit of physics magic in there some how! Things I > notice when playing around with the snowplow: > > - The suspension at each tire is modeled independently. > - The suspension reacts to surface properties ... like smooth > pavement, rougher grass, etc. > - If you drive into a lake or ocean you sink. > - If you drive off a bridge you dive end over end pretty > realistically. > - When you corner, the individual suspension elements seem to react > correctly. The front outside tire seems to dig in as you turn sharper > and sharper. > - As you corner more and more sharply, you need more power to maintain > the same speed. > - If you turn too sharply, you can actually roll the vehicle ... and > visually, it looks very realistic. > - The vehicle reacts to wind. > - There is great interaction between the larger vehicle/body dynamics, > the individual suspension components, and the surface. The vehicle > reacts correctly to slopes and change in terrain. I caught one view > where I was driving over the edge of some detailed road I created for > a day job project and there was a lot of slope/surface variation in > the triangle mesh. Watching this big truck barrel over that with the > body and suspension all working together ... visually it looked "right > on". I wish I would have been able to capture that particular > sequence as a movie, but it's one of those sorts of fleeting things > and it's difficult to reproduce the exact same sequence of speed, > vehicle path, and view point. > - So then if you poke around our aircraft fleet, you find a catalina > and a beaver on amphibs ... you can literally take off on wheels, > retract them, and land on the pontoons, take off and land back on > wheels. Oh, and there's a few helicopters available too. So I'm not > saying everything is perfect, but it's a pretty darn good little > general purpose physics engine. > I fully agree, I was surprised when I modeled the Jeep how well the gears and suspension work. What's missing right now is a proper simulation of transmission and gearshift (it's a jet engine right now).
IMHO YaSim is a good base to implement any kind of ground/water vehicle FDM. > I would also comment that my day job (well until my contract expires > in June) [sniff, hand me another box of kleenex ... actually more like > break out the champaign] :-) involves taking care of a very expensive > commercial driving simulator. In my best estimation, the YAsim based > snowplow captures or models many more dynamics effects at a much > better detail level and realism than this big fancy driving simulator > we use for human factors research. (And we spent close to $250k when > it was first installed and probably a couple more $100k in the > subsequent years on improved hardware and software.) > > > I think a person could do a lot worse than looking over Andy's > shoulder to see how he took care of the gear/suspension/wheel dynamics > portion of YAsim ... it's really pretty darn good. Now I'm going to > guess he's not modeling things like tire flex and some of the really > subtle details some people get into ... there's always room to nitpick > anything. I don't bring this up to nitpick, but to fend off the > potential nitpickers in advance. :-) > > Regards, > > Curt. > -- > Curtis Olson: http://baron.flightgear.org/~curt/ > Unique text: 2f585eeea02e2c79d7b1d8c4963bae2d > ------------------------------------------------------------------------- > SF.Net email is sponsored by: The Future of Linux Business White Paper > from Novell. From the desktop to the data center, Linux is going > mainstream. Let it simplify your IT future. > http://altfarm.mediaplex.com/ad/ck/8857-50307-18918-4 > _______________________________________________ Flightgear-devel mailing list > Flightgear-devel@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/flightgear-devel ------------------------------------------------------------------------- SF.Net email is sponsored by: The Future of Linux Business White Paper from Novell. From the desktop to the data center, Linux is going mainstream. Let it simplify your IT future. http://altfarm.mediaplex.com/ad/ck/8857-50307-18918-4 _______________________________________________ Flightgear-devel mailing list Flightgear-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/flightgear-devel
