Hey, thanks for dropping by my SB. The vanishing guidelines were all done with straight edges to set everything up, and the ellipses were done with the ellipse guide, since doing solid ellipses freehand in PS is impossible, ha. All the detailing lines were freehanded. It's taking a while to do, so hopefully it doesn't turn out to shit.
Now, on to your work. Very cool style you're starting to develop, man. It's almost graphic in nature, but you're working very hard on construction and perspective studies which is SO important. Just always be very technically minded when doing studies. Be as precise and meticulous as you can be with your lines and perspective, that way when you go to sketch in perspective or just draw normally you'll have all that hard work under your belt and it will be much easier and fluid to do so. I like the robot sketch too; kinda funny, ha. The colors are looking quite nice; midtones have a nice saturation to them and the shadows have good color to them as well. Just keep pushing your values to be more and more contrasting and "real". Enough of my rambling. Great work, keep it up!