These are some of the  best 3D photoshop tutorials that you can find online. As a designer you can find almost all kinds of 3D stuff to polish your 3D designing skills.
3D Typography in Photoshop

Tutorial 3D wireframe Justice cross. Illustrator + Photoshop

Creating a 3D Textured Environment in Photoshop

Create a Robotic 3D Spider

3D Transparent Glass Text [...]

If you are looking for inspirational 3d Robot designs ,  here is the list of  35 Amazing Examples of Modern 3D Robots
Concept Robot – Created by Billy Cheng

Cockroach ‘07 – 3d Artist: Dennis Hoppe

Urz-t  by Dorn

Robots – Created by Mihail Popov

Robot Hopper – Created by Tristan Bethe

Scorbot – CG Creation by Saeed Hasan Zadeh

Robot by [...]