The Processor or Controller or Control Logic
For any robotic project it is important that the working logic be flexible enough to allow changes and modifications. In order to achieve that, a microcontroller is employed and the working algorithm is programmed into it using either assembly language or C language.
In India the most commonly available microcontroller is the 8051 and its variants. There are a lot of books out there and the internet is full of information so I wont try to explain the 8051. Google it! Also download the datasheet if you can.
I made a module for myself that I could reuse since I could have numerous project that needed a controller and I was not going to start putting the crystal and reset ckts again and again. Re use means that after I make a project, I take pics and videos and disassemble it and head for the next project.
I made the circuit on a general purpose veroboard and the ports can be attached using burg-strip connector as shown. I have used a 40-pin ZIF socket to avoid damaging the controller in handlling.
The Schematic is not necessary here since there is only a crystal and reset circuit attached to it. The controller and connectors should suit your style of working and needs.
Another good example is the arduino. The arduino is an open source, AVR based prototyping platform that has become a standard on its own. The location of the connectors and connections have been fixed and all supporting boards or shield boards being produced follow the same pattern to allow compatibility and standardization.
At the end of the day it is your choice but I really suggest to get started, work with existing patterns. If you plan to use an external programmer as I did, a ZIF socket will be a good idea. If you have not thought about exactly how flexible you want to make your design or what else you might do then focus on the project at hand. Its all a learning exercise.