I have a very small scene, just 3 cubes moving, and bumping into a larger (low poly) object. I set steps and iterations to 1000. But the collision results are still not perfect. (one part interfering with an other by many mm).
Speed is not important for me in this case. How do I have to ajust the system for highest precision collision detection results?
Check the collision margins on the objects. By default it’s 0.04bu
Also note that the Blender docs state that objects smaller than 1 cm will have problems with the physics engine. That seems to be the limit, so you have to scale everything up.
convex hulls can only represent a object that is not concaved,
if you want accurate bounds on a terrain, try making the physics bounds out of many convex hulls, and simple physics bounds like cube, sphere when you can get away with it, one graphics mesh, may end up using many smaller objects to add up to its physics bounds.
turn ond visualise collision bounds in the game menu,
Raising the number of sub steps isn’t the entire story when it comes to BGE physics.
You can also set the physics ticRate to a very high value as well so you have very precise collisions (even in high speed situations). The downside though is that physics in general will become a bit slower (since there’s more calculations done every second).
Thank you all for your valuable help.
Geometries were sub 1cm indeed, so I scaled/applied, and it seems that collision calculation between moving objects and my fixed geometry is perfect now.
But I still have large interferences between some moving objects. How can i avoid that? I am using Mesh/Final. Interestingly, more iterations don’t necessarily give better results.
Where can I change the tickrate?
I have seen something that might have caused the problem: when my moving objects start moving they already are colliding (even in step 0 already). When I change that (no collisions at step 0), then the inter-moving-objects-collisions are much more precise it seems.
Another question: how can I reduce “bounciness” of colliding objects? Especially when they cannot escape the colliding situation any more they start to flicker/bounce very much. That increases the danger to get a collision where in reality there should be none.
I set mass to 10000 and friction to 1, but it didn’t help.
Did you give the collision bounds a little extra margin? Try playing with the value, from say 0.005 to 0.1 beyond the object’s actual bounding dimensions.
Yes, that enhanced it a lot. Set it to 0.25.
How can I make the objects less “bouncy” between steps? I think the bounciness is a problem (they can jump into interference situations).
I set “Bounciness” to 0, but doesn’t make a difference.
Bounciness can be caused by very large polygons such as terrain. Things colliding should have faces about the same size. Use collision meshes if required.
Also check elasticity in the material properties.
You can try increasing the damping. I find 0.7 on rotation often works relatively well.
Can we see a blend. Remote debugging is quite hard.
Here is the blend. The golden geometries shall move versus the blue ones and not have any collisions between them at the end position (they are following path curves). They are moving until frame 100, but I have seen that I get better final collisionfree positions if I let the simulation run a bit longer, until frame 250.
Here, at frame 250, the result looks about perfect, but I fear its just a little bit of good luck. If you go back to frame 190 for example, there is at least one large interference, and I’d like to avoid that completely. I don’t care much about speed, just precision.
i get better results if I increase solver steps per s from 20 to 100 (iterations stay at 30).