Costly collision model

From Valve Developer Community

A costly collision model is one with over 20 convex parts. You will receive this error when going over it:

WARNING: COSTLY COLLISION MODEL!!!! (30 parts - 20 allowed)
WARNING: Error with convex elements of myfirstmodel-phys.smd, building single convex!!!!
Model has 31 convex sub-parts
Collision model completed.

The appearance of "error with convex elements" is itself an error, so ignore it. Your meshes are (probably) fine.

Solution

Either try to decrease the number of convex meshes, or if you really do need that many of them (usually only excusable on very large models), to use the $maxconvexpieces command to override the limit to one of your own preference. For instance:

$collisionmodel	"myfirstmodel-phys.smd" { $concave $maxconvexpieces 30 }

 Note: Episode One engine users must run studiomdl with the -fullcollide parameter when compiling instead.