Like many other complex systems, a full-blown robot is comprised of several separate systems working in tandem. For one person to be or become an expert in all would be unreasonable, at least for a standard mortal. Depending on your particular inclinations, different areas may be more or less suitable for exploration. There is also the question of specialisation versus broad-oversight, as well as that of making custom components versus using ready-made ones. Some particular areas to consider are:<p>(a) Vision systems, which further subdivides into hardware and software components. The industry could use some better performing cameras (think low-light, high frame-rate) with reasonable prices, so that is one area needing development. Popular software systems, such as the open source OpenCV, definitely need work.<p>(b) Audition systems. Since there is already quite top-notch audio hardware available at reasonable prices, I opine that the software side is more in need of serious help, particularly in the areas of speech recognition.<p>(c) Vocalisation systems. More natural and emotional voice-production systems would be nice, particularly if available open source.<p>Note: Both audition and vocalisation have open areas for less-popular languages. These systems really ought not be limited to English.<p>(d) Basic mechanical systems, which subdivides into functional and aesthetics. There is certainly room for improvement here.<p>(e) Electrical systems, such as wires, motors, and relays. There are also interesting developments here such as synthetic-electric muscle fibres -- both mechanical and electrical.<p>(f) Testing. Like many other complex systems, there is often a need for testing.<p>(g) Psychology. If the machine interacts directly with humans or other animals, there is an element of psychology involved, even in simple systems such as automated tellers.<p>(h) Environmental impact, both in production and deployment.<p>(i) Security. If the system is accessible to the public in one way or another, then security probably matters.<p>(j) Artifical intelligence and other broad-level perspectives. This area is related to game AI, and it applies to both robots and fully-virtual systems alike.<p>... And quite a few other areas.