Trigger Collision is colliding with AI characters

Since 4.9, I have strange issue with grenades. I have two big radius collision spheres as components for the static mesh (grenade). The grenade collide the right way with enviroment, but those collision spheres collide with AI skeletal mesh actors even I have set the collision as trigger and also tried with overlap all. If I disable the collision for spheres, the grenade fly correct again.

I tried to enable those spheres when the grenade is about to explode (so can check nearby actors), but even I enable only query the nearby AI actors get pushed away from the collision area. Using mixamo fuse characters if that have some strange effect.

Hello SaOk,

How do you have the collision on your AI set up? Are you ensuring that it is not set to block your grenade’s collision?

AI characters have capsule set pawn and skeletal mesh as character collision. Those shouldnt block the grenade trigger volume when the grenade trigger volumes have overlap all setting, but they do.

Update - Its the pawn collision that blocks those trigger volumes. I set collision to “ignore only pawn” for the trigger volumes and seems I can now manage proper grenade behaviour that way. Still seems like a small bug?

The character mesh is set as a Pawn object type by default if you have a look at the expanded Collision tab in the character blueprint. This is why you’d have to set your collision to ignore the pawn in order to prevent the object and the character from colliding. Any time you want to have two objects interact with one another, each object’s collision needs to be set in such a way that they are able to either collide, overlap, or ignore one another. Hope that helps explain the reasoning behind your issue.

Yes, but it seems pawn still collide even the colliding object have collision that should overlap pawn. So overlap pawn setting seem to work wrong since 4.9 for me. Ignore pawn works, but not overlap pawn.

You could test it by creating physic object that have big volume around it with overlap pawn collision setting. If you walk to the object it should move before reaching it.

Are you sure that the pawn is set to overlap whatever the grenade’s object type is?

Yes, 100% sure :slight_smile:

Grenade static mesh (physicActor) overlaps dynamic and pawn.
Volume (component for grenade) overlaps all.

AI actor capsule (pawn) overlaps physics, dynamic and pawn.
Skeletal Mesh (component for capsule) also overlap the same as capsule.

I’ve done some investigating, and it turns out there is actually a bug in our system, UE-21559, that relates to sphere components and player capsules having some collision issues, which could explain the behavior you were experiencing. Is it possible for you to either create a video, or zip up a test project that shows the bug so that we can confirm that it is the same bug? Thank you.

Hi, yes sounds like the exact same bug. Its the capsule that collide with the sphere, not skeletal mesh. Also box component is having the same issue. Made video, bit bad vid but you can see the bumerang effect unless not throwing at the AI characters.

Could I get a screenshot of the components tab of the grenade blueprint? Try using a scene component as the root, and then parenting the mesh and the volume as children of the root.

Sure here, for sphere also have tried overlap all dynamic, overlap only pawn, trigger and custom. Also object type world dynamic.

EDIT: Will try that scene component as root.

I have tried to reproduce your issue in a new project, but was unable to. Could you try to create a new project with just the character and grenade and see if you still have the same issue? If you are having the issue, please zip up the project and send it my way so we can have a look at it and see exactly what the issue is. Thank you.

I tried to have scene component as root, but couldnt make the grenade fly then. But as strange effect, when I returned to old structure (as in that pic) now the grenade seem to work as intented. Overlap all for sphere no longer collide with pawn. :S

Did you make any changes when you re-did your old structure after trying the scene component as the root, or did you reset it to exactly what it was?

Just removed the scene and moved the old components to have old structure. But earlier I made the pawn to ignore physics actor. Could be the sphere in grenade was somehow detected as physicsActor even only its root (the mesh) is physicsActor. Seems like it inherited the root collision settings.