Вот так попробуй
obj.phisobject = New phisObject
obj\mesh=child
mesh=CopyMesh(child)
obj\phismesh = BodyCreateHull(mesh,10)
EntityAlpha mesh,0
phBodySetPos(obj\phismesh,EntityX(obj\mesh,1),EntityY(obj\mesh,1),EntityZ(obj\mesh,1)
phBodySetEntity(obj\phismesh,obj\mesh)