Do I need a separate collider object?

[Sharpy]

I've modelled a part, which is rather simple, but needs a pretty precise collision model (is to fit another part snugly). As result, the collider surface is identical to the part surface - can't be made any simpler, and doesn't need to be made any more complex. Do I need to create a copy for collider, or can I just reuse the same model?

[Sharpy]

Ok, answering my own question, I don't. The same mesh can be reused for mesh collider.

[SpaceMouse]

I think Unity in many situations simplifies the mesh itself. I've tried to do a concave collider before and unity definitely flattened the bottom out. complex shapes can be done with a number of simpler shapes. I've had to do that before.

[Sharpy]

11 hours ago, SpaceMouse said:

I think Unity in many situations simplifies the mesh itself. I've tried to do a concave collider before and unity definitely flattened the bottom out. complex shapes can be done with a number of simpler shapes. I've had to do that before.

Well, it fully worked in my case. The shape has two tiny nooks for attaching struts, and it does take some wiggling to find them, but they are there.

[SpaceMouse]

7 hours ago, Sharpy said:

Well, it fully worked in my case. The shape has two tiny nooks for attaching struts, and it does take some wiggling to find them, but they are there.

Odd. I actually tried it twice,  once with the FFR engine i did for KSPI and once for a centrifuge piece i made for rovers. Had to use a number of smaller ones to get the collider close to correct. 

[Sharpy]

@SpaceMouse

*shrug* I believe it may be the engine's definition of 'convex'. I'm not sure if Unity uses this definition, but I found it used in mathematics, and in computer science:

[note not "concave". In that definition, "concave" is not an antonym of "convex".]

Meaning, there's at most one collider surface on the path from the surface of the collider to some arbitrary center. Maybe middle of the collider object. In my case, the notches being far away and pretty much in line with the center of mass, the cut-off would be minimal.

 

The MK3 cargo bay collider, for example, is actually not even continuous, just a whole bunch of boxes (cuboids).

(My part is a "payload" that is to fit MK3 bay, so I loaded the MK3 collider and made my part to match its dimensions. At first I considered just inverting the MK3 collider and shrinking it slightly, but gave up on that when I saw the mess it is.)

 

 

 

 

Edited September 26, 2016 by Sharpy

[Van Disaster]

Your "Not convex" collider can be made out of three box colliders - box colliders are *much* cheaper than mesh colliders anyway, so that is not a bad thing. But yes, mesh colliders have to be convex polygons ( no interior angle greater than 180 degrees ).