Roblox defying physics?

DarkWatery · January 20, 2021, 1:51pm

Hey pals! It’s DarkWatery…
Recently I was planning to build a Roberval Scale.
For those who don’t know, it looks something like this:
rober03c

I built this basic frame in Roblox Studio:

However, it turned out, that the part, just fell through the cylinder:
Roberval

The time I clicked it, i unanchored it by pressing “Alt+A”, and it just fell down thorugh the cylinder as you may have seen. The part is a union.

Is this the case with everyone? Did Roblox just defy physics?
I am curious to know, as I want to build a Roberval Scale in studio.
Is it because it’s a union, if yes let me try it without doing a union.
Help is greatly appreciated!

Thanks and Regards.

Aegians · January 20, 2021, 1:53pm

But what is the reason for using a union here?

DarkWatery · January 20, 2021, 1:54pm

To form that hole you see. The hole in which the other cylinder is inserted.

Aegians · January 20, 2021, 1:55pm

Both are CanCollide… correct?

DarkWatery · January 20, 2021, 1:57pm

As you see, it works without a union, but why not with the union?

0_salcret · January 20, 2021, 1:59pm

Unions tend to have ‘sloppy’ hitboxes, it might be more precise if you import a mesh instead.

DarkWatery · January 20, 2021, 2:05pm

Alr, lemme try it with booleans in Blender, and import it.

Discgolftaco231 · January 20, 2021, 2:28pm

go into the Union’s properties, and find CollisionFidelity. Change the dropdown to PreciseConvexDecomposation. This can be heavy on your CPU, and your CPU is what is calculating physics. However, of it is only like 5 unions, you should be fine.

@0_salcret is correct though, Unions have bad collision hitboxes. you might be better off with a mesh.

DarkWatery · January 20, 2021, 2:32pm

It’s just one union tbh. And yea about meshes, I haven’t tried it yet, will do!

KhanPython · January 20, 2021, 4:13pm

I just tried replicating your structure with unions & everything seemed like it worked for me
https://gyazo.com/e72cfaeddf5bd4e39d30f5d7e97e43b7
As @Discgolftaco231 mentioned, make sure you have your CollisionFidelity of the union part set to PreciseConvexDecomposation

KhanPython · January 20, 2021, 4:20pm

As far as I remember, the geometry for the unions are calculated the same way as they would be for a mesh. It wouldn’t make a difference, although it’s still advised to move away from the Unions as you’re saving extra data of previous parts that came together in order to create that union, which may potentially eat up your memory. You may still use unions for simpler things though (e.g. hole through the wall/ground or an object), just avoid them as default means of modelling.