[ODE] hinge-2 and coordinate systems

[Timothy J. Wood]

On Thursday, July 25, 2002, at 06:52  PM, maddocks@metservice.com wrote:

> I use real world values for everything. Mass, gravity, torque etc and 
> everything works great;) It really was a great feeling the first time I 
> drove my car around. The thing that a lot of people say though is that 
> you should keep values between -1...1 otherwise you will have problems. 
> I haven't struck this yet and I have no clue what I'm going to do if I 
> do start having problems:(

   Yeah -- the problem was that I was starting to do this, but hadn't 
finished.  In particular, I'd changed gravity to -9.8 m/s^2 instead of 
the -0.5 m/s^2 used in the test app.  I didn't change any of the other 
constants, though, so I overwhelmed the suspension on the hinge joint :)

   I'm not sure it is reasonable to require small values -- sure they 
shouldn't be astronomically huge, but you should certainly be able to 
create a tank and specify that it weighs 10 tons (or whatever).  If 
nothing else, it would be nice to have a system-wide scale factor to 
bring stuff into the range that ODE likes.

   I also note that ODE performs operations that generate FPU 
exceptions.  I really like having FPU exceptions enabled in my apps so 
that I can catch divide-by-zero, sqrt(<0) and such early.  I had to turn 
it off to use ODE, though, since ODE was performing operations on +Inf.  
I didn't take the time to look at it, but maybe I will in the future 
after I actually prove to myself that I can make something interesting 
out of ODE :)

-tim