How do I design a robot from scratch instead of just following plans?

There is a real difference between reading a map and drawing one. Following a design uses one set of muscles; starting from a blank page and a list of requirements uses another. Feeling overwhelmed does not mean you lack the ability. It means you are standing at the widest part of the problem, where everything is still possible and nothing is decided yet. The overwhelm comes from trying to hold the whole robot in your head at once. You do not have to. Every good designer breaks the machine into smaller questions: how it moves, how it senses, how it is powered, how it holds together. Answer one at a time and the fog thins. Start with the single most important requirement, the one the robot exists to meet, and sketch only the part that serves it. Ignore the rest for now. Once that piece is real, the next question will be obvious. You build the whole by finishing one small part you can actually see.