[ODE] Jitters

Geoff Carlton gcarlton at iinet.net.au
Tue Nov 9 12:44:00 MST 2004

Be careful of huge mass differences and in particular very small 
masses.  I guess you can't help it if you really do have a huge 
difference (e.g. a church tumbling around in the air).  However you 
could group objects into small/huge sets and special case the result so 
that a "basketball-church" collision is treated as "basketball-null".  
Thats probably going to work better than any mass difference could do, 
and it means you can keep the masses around 1-100 units (which is what I 
use and find to be stable).

Tim Rightnour wrote:

>On 08-Nov-2004 Geoff Carlton wrote:
>>What is the mass?  If its very small then even 0.01x the velocity can be 
>>too great a force (I've seen this with very small objects).  Try a lower 
>>value for both linear and angular, and see if it fixes it, (e.g. -0.001).
>>Judging by the results it looks like the -0.01 is providing way too much 
>>force and the object is flying in the opposite direction each frame.
>Looks like you were dead on.  I guess I forgot that I was applying force
>directly to the object, not just modifying it's linear velocity directly.  My
>masses are all rather minute, due to me trying to keep them between 0 and 10. 
>It means my light objects all have infitesimally small masses because they got
>normalized against things like houses and churches.
>I still can't make the jitters go away, but perhaps if I play with the damping
>forces some more, I can find a value that magically works.
>Stupid me.  My old physics code just had me working directly with linear
>velocity, not applying force, I guess I got it confused in my head.  Thanks to
>everyone for helping me find where I went wrong with the damping.
>Tim Rightnour <root at garbled.net>
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