Now you have a rough sketch of the robot and the block diagram, you are ready to start choosing the parts you would use to build a robot. Throughout this book, we have looked at the trade-offs between different kinds of sensors, different chassis kits, controllers, and so on. These are trade-offs on weight, complexity, availability (you don't want a part that is irreplaceable), and cost, which were covered in detail in Chapter 6, Building Robot Basics - Wheels, Power, and Wiring.
If the robot has been inspired by a particular kit—for example, Spiderbot was inspired by me being sent such a kit—then this will possibly constrain the other part choices you need to make. It is clear that I'd need to support 18 servo motors, however, at the time of writing, a 16-motor controller was available, so I elected to use two IO pins of my controller...