Colliders with same root object won't collide unless root object moves.

Questions & Answers
1

I have a system that works something like an old radar screen with a sweep and blips only it’s on the edge of a cylinder instead of the top of a disk. The sweep loops around and while it’s over a blip the blip should light up.

However the sweep collider won’t trigger the blip collider unless the parent has moved.

Cylinder
 -> Sweep 
  -> Mesh Collider (is Trigger = true)
  -> Script to rotate around cylinder
 -> Blip
  -> Capsule Collider (is Trigger = false)
  -> Rigidbody (Use Gravity = false, Is Kinematic = false)
  -> Script with  OnTriggerEnter set light on, OnTriggerExit set light off.

Even though Sweep is moving through the Blip the triggers on the Blip are not being called.

I then add small jitter script to the cylinder. Every update it alternatingly moves the cylinder either up 0.0001 or down 0.0001 causing it to move slightly up and down in place. With this in place everything works and the blip lights up and turns off as the sweep passes through it.

How do I make this work properly without the jitter script?

2

Like Translate, Rotate just teleports colliders around. If you want the collisions to be detected properly, give the cylinder a rigidbody and set its angular velocity. Then the engine can properly check for collisions.