I don’t know if it’s the right category and tags but never mind. can someone please explain me, why can’t I simulate physics on actors that uses complex collision as simple? I have a ram skull which I downloaded from Quixel bridge and I tried to edit it in blueprint and add some functions to it but when I try to simulate physics on it (via the blueprint) it’s says error. it cannot simulate physics on complexAsSimple collision. And I need the complex collision I don’t want to switch to simple box collision I need to keep the complex. anyway to solve this problem?
You need to either export the mesh and add custom collision in Blender, 3DSM or other 3D modeling software, or add primitives to it in the SM editor. A simple convex collision from the sm editor will work.
There’s loads of tutorials on this.
1 Like
why can’t I simulate physics on actors that uses complex collision
That’s how the engine is set up. It would be too taxing to simulate on millions of triangles in real time. You can simulate against complex (a ball rolling down very complex terrain) but the terrain cannot simulate itself.
It does not need to be a box:
The auto-convex can generate more advanced shapes, too:
But the best advice is in the previous post. If you need custom and accurate collision that is also performant, look no further than this:
2 Likes
I have noticed that I am getting the same problem with ComplexAsSimple collision, but I have noticed on my object that there is a button for me to change its collision complexity. Would you recommend that I click on that and then press on “Project Default”, “Simple and Complex” or “Use Simple collison as Complex”?
(Just showing how it looks like on my end)
I am getting the same problem
What problem? Complex Collision is static and cannot be simulated.
- if we have a bunch of immovable craggy rocks players needs to navigate on with a high degree of fidelity, and one cannot be arsed to laboriously craft neat collisions, use
Complex as Simple - if you need something to move, rotate, simulate, interact with other entities or be overall performant, stick to
Simple Collision. There’s a bunch of different ways to get the correct collision shape:
2 Likes
Hmmm okay, good to know. Thank you 
Collision hell.
UCX is the answer. It’s always the answer. This is how you can simulate a complex mesh in UE.
In whatever program you use for your mesh making, just make your collision mesh to your preference and give it a UCX tag like this:
LargeWheel
UCX_LargeWheel
and export them selected together as FBX. Unreal will automatically use the UCX model as the simple collision.
Never change this epic. Please don’t change this
1 Like
Or give us a tool we can make UCX inside the editor with. We can already edit brushes somewhat efficiently… it’s not that different.
1 Like
Ah this would be nice. All I wanted to do was make a wheel that rolls very smoothly but without a sphere collision because of all the potential overlapping and issues.
I then spent ages working with the chaos vehicle pipeline and noticed that for wheels you can set a static mesh cylinder as the wheel’s collision mesh in the BP_wheel component that comes with the chaos vehicle setup.
I toyed around for ages thinking maybe there’s a blueprint way to attach a custom mesh as a physics simulated collision but no avail.
Then I discovered this thread and it was like my brain just deflated like an old football… I felt so dumb.
I don’t know why I never came across this in any of my time going through the beginner courses provided 