How to fix mesh collision problem?

[AbandonedRick (Rick)]

I made a mesh in blender and tested it out by walking on it but it seems that the collisions are off.

[Images above: Player “floats” in air when walking over the mesh and only steps onto the mesh at the highest and lowest points.]

I understand that it is something about Roblox rounding off the collision, so is there a solution to this?

[nurgenius]

There have been tons of these threads, and there are many solutions, please use the search tool next time. Here is one explanation and solution:

How to fix unwanted collision for MeshPart?

Roblox uses Approximate Convex Decomposition (for CSGs and MeshParts), meaning that every shape will use only convex chunks (1). It cannot create concave chunks, it can only imitate concavity by breaking the shape into mulitple convex chunks. To achieve more precise concave shape imitation you need to split the mesh at concave areas. This will allow ACD to create convex chunks at a smaller area, resulting in the collision shape being more credible to the actual mesh shape. (1) There are 3 Co…

Here’s another:

Mesh collision problem

If the entire map is one big mesh, you’re going to have a problem. The collision shape of a mesh is different and less exact than the actual shape of the object–you just don’t notice it because meshes are rarely big enough to cause a noticeable difference. It’s similar to how cutting a hole in a wall with CSG would make it impossible to walk through. You could try breaking down the mesh into smaller chunks, but I’m not sure how well that would work. A better option, though tedious, is to disabl…

And here is my personal approach:

@nurgenius

The original mesh being collision disabled and importing a mesh using this plugin https://www.roblox.com/library/267728602/Physical-Obj-Importer to turn the mesh into parts. Meshes still don’t have good collisions, so use parts as collisions until that happens.

[AbandonedRick (Rick)]

Thanks for the answer, I think I’ve found the solution I’m looking for.

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@nurgenius

please use the search tool next time

I do want to clarify that I did use the search bar and only managed to find threads from Platform Feedback about improving mesh collision detection.

Anyway, thanks for the solution, now I can continue my development without worrying about how to solve this collision issue. Thanks!

[1Joeb (joeberson)]

Let me know if the solution works out for you, I am having the same problem.

[AbandonedRick (Rick)]

Hello,

Yes, the solution works. What I did, was to gauge which parts looked concave and separate them into two different meshes.

Here’s a visual representation:

[Image 1: Combined together as one mesh, the player walks over the purple area.]

[Image 2: Splitting the parts at concave areas (the purple part) allows for better collisions.]

Do note that if you have irregular meshes just like mine, the more you separate the meshes, the better and more accurate the collision becomes.

[Dev_Rig]

Really sorry for bumping this but, i’ve been trying to figure out why my tram mesh for my railway kept having invisible walls, even with precise collision on, i split my mesh in two and it worked perfect after that.
I’m just really curious at why this does this…

[IsaacFantasy]

Hi, I’m here to share a solution I created.
Open your model in Blender(or any 3d editor)
Duplicate the original model.
then split all the faces of the model (NO need to separate into different objects) and resize them a bit to add some offset between each face.
Import this model to roblox and set the collision fidelity to PreciseConvexDecomposition.
Them use this model as collider for your original model (make it invisible, place in the same position as the original, set the original CanCollide as false … etc).

PS. If the offset is too small it doesn’t work
Maybe You can Import a giant model with good offset and resize it to avoid this problem and get a small offset not sure.

Original Model

Collider

Final Result

[Quellyxx (Quelly)]

The only one simple enough to use quickly! This solution is awesome. Thank you!

[cmdr33]

i found a solution that will help you save half the usage of that model (you basically needn’t the double copy solution)…

find out how to use this script in blender:

import bpy, bmesh
from bpy import context
from mathutils import Vector

bounding box helper methods

def bbox(ob):
return (Vector(b) for b in ob.bound_box)

def bbox_center(ob):
return sum(bbox(ob), Vector()) / 8

def bbox_axes(ob):
bb = list(bbox(ob))
return tuple(bb[i] for i in (0, 4, 3, 1))

def slice(bm, start, end, segments):
if segments == 1:
return
def geom(bm):
return bm.verts[:] + bm.edges[:] + bm.faces[:]
planes = [start.lerp(end, f / segments) for f in range(1, segments)]
#p0 = start
plane_no = (end - start).normalized()
while(planes):
p0 = planes.pop(0)
ret = bmesh.ops.bisect_plane(bm,
geom=geom(bm),
plane_co=p0,
plane_no=plane_no)
bmesh.ops.split_edges(bm,
edges=[e for e in ret[‘geom_cut’]
if isinstance(e, bmesh.types.BMEdge)])

bm = bmesh.new()
ob = context.object
me = ob.data
bm.from_mesh(me)

o, x, y, z = bbox_axes(ob)

x_segments = 2
y_segments = 2
z_segments = 1

slice(bm, o, x, x_segments)
slice(bm, o, y, y_segments)
slice(bm, o, z, z_segments)
bm.to_mesh(me)

bpy.ops.object.mode_set(mode=‘EDIT’)
bpy.ops.mesh.separate(type=‘LOOSE’)
bpy.ops.object.mode_set()

thank me A LOT later…