The error "Unity 3D collision not working" usually refers to a situation where objects in a Unity game aren't interacting as expected, often passing through each other instead of colliding and responding appropriately. The causes behind this issue may include:
Inappropriate Collider or Rigidbody Settings: In Unity, collisions are primarily handled by Collider and Rigidbody components attached to game objects. If these are misconfigured, collisions might not work as intended. For instance, if the 'Is Trigger' option is enabled on a collider but no appropriate script handles the trigger event, or if neither of the colliding objects has a Rigidbody component, collisions may not occur.
Layer-Based Collision Rules: Unity allows defining which layers can collide with others. If your objects are on different layers and those layers are not set to collide in the Physics settings, they will pass through each other.
Incompatible Physics Settings: Some global physics settings could also interfere with proper collision detection, like the minimum penetration for penalty setting.
Incorrect Collision Detection Mode: If using a Rigidbody, its collision detection mode may be set inadequately for the specific needs of your game. Fast-moving objects may require 'Continuous' or 'Continuous Dynamic' modes to correctly detect collisions.
Resolving the "Unity 3D collision not working" error involves checking and correcting the aforementioned potential issues:
Check Collider and Rigidbody Components: Ensure that both objects involved in the collision have appropriate collider components attached. If they need to interact physically, at least one should also have a Rigidbody. Make sure the 'Is Trigger' option aligns with your needs for the object's collision behavior.
Inspect Layer-Based Collision Rules: In the Physics settings, verify layer-based collision rules to confirm that the layers your objects reside on are allowed to interact.
Adjust Global Physics Settings: Review your global physics settings in Unity. Try adjusting settings such as the minimum penetration for penalty or bounce threshold to ensure they're not preventing your collisions.
Set Proper Collision Detection Mode: For fast-moving objects, consider setting the collision detection mode on the Rigidbody component to 'Continuous' or 'Continuous Dynamic'.
Remember to test your game after making each change to identify what solves the problem.