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
> 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
> problem, so it's useful and interesting to see how others
> approach the
> 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
> - 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
> 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. :-)
> Curtis Olson: http://baron.flightgear.org/~curt/
> Unique text: 2f585eeea02e2c79d7b1d8c4963bae2d
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