Can Custom Collisions Simulate Physics?

Development World Creation
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Hi, I just made a Pirate Ship and I ran into the problem that UE4 creates autimatically only CONVEX collisions but no Concave, and “Use Complex Collision As Simple” doesn’t work with physics… So I did my research and figured out that I can create “Custom collisions” with blender adding a bunch of boxes wherever i want to have collisions.

Creating custom collisions for my Ship would take me hours, so before I do that I wish you could tell me if I will be able to simulate physics with my custom collisions

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2

Hi! The simplest approach you can use is smth like that

  • evaluate collision parts in Blender (for example approximate all geometry with boxes, spheres, capsules)
  • add all them in asset editor as Primitives for Simple Collision

Only Simple Collision is used for Phys Calculations. As for using Convex collisions - it is optimization to gain effective way of testing collisions. With concave geometry it is much more difficult to check that out )

3

evaluate collision parts in Blender
(for example approximate all geometry
with boxes, spheres, capsules)

This ^^^, but another way to speed it up or augment the process is to use UCX.

  • duplicate the mesh in the modelling app and decimate it / optimise it - reduce the complexity with whatever tools you’ve got available
  • this will hardly ever be perfect (and can get messy) but will give you a rough shape to work with so you do not need to start with primitives
  • you’ll need to put some extra work to make it neat, clean it up and add / remove vertices where it makes sense
  • remember to disable auto generated collisions when importing the fbx

Somewhat related tutorial, here the collision is made from scratch, but mesh decimation can give it a boost if the model geometry is really complex and you require fidelity:

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Whether it’s worth the time depends on your modelling skills and experience. For a shape like the ship above, I’d probably do it manually by extruding faces as needed. Shouldn’t take more than 20 mins, probably less.

Things get less funky if you need to do 20 or more of these, though…