Problem with shadows

Hello Guys, i’m developing mobile game and have faced one stupid problem…

There are black spots on my model and i dont know how to avoid them…
I know that i can change Smoothing Angle but its not the solution becouse my game should not be smooth. And i also know that i can set the Normals to “None”, but in that case everything become black(on my phones screen).
So… Hope u will help me and i also apologise for my English.

You need to flip the normals of the dark surfaces.

They are currently treated as facing outwards, that’s why they are dark. In your 3D software, mark the problematic surfaces, and find something like “Flip Normals”.

What software are you using?