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Collision does not work with Actors that are attached to other Actor

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    Collision does not work with Actors that are attached to other Actor

    I'm using UE 4.7.6. I encounter a problem with simple collision. The steps that I did are as follow:

    1. I create an Actor blueprint (let's say Actor1).
    2. I add a Scene Component inside Actor1.
    3. I create another Actor blueprint (let's say Actor2).
    4. I add a Static Mesh Component inside Actor2.
    5. I enable the BlockAll collision preset on Actor2.
    6. On the level editor, I created 2 instance of Actor2 (let's say Dummy1 and Dummy2).
    7. Then I create a new PlayerController blueprint.
    8. Inside that PlayerController blueprint, I created a keyboard event listener. For example, I would do something if I press K key.
    9. From that node, I created another node called Add World Offset so I can change the location of Dummy1 to get closer to Dummy2.
    10. The collision works perfectly. Dummy1 will never get pass Dummy2.
    11. Now, I attach a dynamically spawned instance of Actor2 to a dynamically spawned instance of Actor1 (Actor1 become parent of Actor2), by using Attach Actor to Actor node. I repeat this step twice to get 2 instances of Actor1 (Dummy3 and Dummy4).
    12. I revise my PlayerController blueprint to alter the location of Dummy3 to get closer to Dummy4 by using Add World Offset node.
    13. The collision FAIL. Dummy3 can go through Dummy4 as if they never collided.

    Is this an expected behavior?
    If it's a bug, is there a workaround for it?

    If I understand your situation correctly, you want an attached actor (a child of some other parent actor) to generate collisions? This is not supported by the engine, as far as I know. The child actors do not perform a "sweep" when moving, so they do not detect collisions.

    I have a very basic fix for this in C++, here:

    Sorry that doesn't help much if you're working with blueprints. Epic is aware of the issue and has said in a few posts on the AnswerHub that they are "considering" a fix.
    Level 17 The Ladon Device


      I've run into this problem as well. I'm using child attachments for a vehicle and the attached parts do not react to collisions. If child actors do not work for this can someone recommend an alternative method?