This tutorial shows how I draw robotic/futuristic legs, arms, robots, vehicles, and so on for. This technique works well for side views of anything with joints, so it doesn't only apply to robot legs. I tend to draw these things as concepts or just to get ideas for 3D models I'll make later (usually for games).
Remember to start off by drawing all the joints first. Draw LIGHTLY so you can easily erase parts that you're not happy with. Once you have your proportions right, start drawing the major parts then keep refining them until you have a detailed drawing. For details you can add pipes, grills, metal plates, bolts, guns, lights, doors, windows, wings, jets, etc.
