Collisions of fast-moving objects

Unity Engine
1

Hello everyone,

I am trying hard but cannot make the collisions of fast-moving object work.

I have a strong academic background on how the physic works and I wrote pieces of software dealing with physics (dynamics, deformations, kinematics, springs etc.) so I think I checked available options thoroughly and consciously enough.
The best effect was to vastly reduce the fixed timestep, but it only pushed the error furher, i.e. minimalized but not solved the problem.

Of course, I came across “Don’t go through things” script:
[http://wiki.unity3d.com/index.php?title=DontGoThroughThings#C.23_-_DontGoThroughThings.js][1]
but I does not do the job in my scenario either.
I analyzed the code a bit, and came to conclusion that it is meant for collision of pairs (static obstacle, dynamic fast moving) objects, not between two fast moving objects.

My setup is:

  • A container which is moving at high speed
  • Multiple small objects which are moving fast too. Their movement is mainly induced by their collisions with walls of the speeding container.

Therefore, plenty of time the objects are in contact with the walls (objects are hit by walls). For instance: If the container has great acceleration, the hit results in immediate objects bounce. If the container accelerates not so quickly, the objects become somewhat sticked to a wall until the container stops and inertial forces come in.

Maybe this is the concern, but this is my game. The collisions are supposed to work.
I have been tinkering with the world/objects scale, materials, colliders, collision models, time-steps. No success.

How such collisions management should be handled in Unity?

Best,
Maciek

2

Hi, welcome to the forum!

There are a few things you can try in order to reduce this problem (you don’t mention exactly which things you have tried already). The Rigidbody component has different collision detection modes that can be used for different collision scenarios. Try changing the mode to Continuous Dynamic on all the moving objects in your scene. If you are using a mesh collider for the container then you might have problems if the mesh is a “skin” with no thickness. You might get better results if you can arrange for the container walls to have some thickness. If this isn’t possible then try reducing the Min Penetration for Penalty value in the Physics settings. Note that some of these techniques tend to have a cumulative effect, so increasing the collider thickness and reducing the time step might solve the problem even if neither change has much effect by itself.