A beginner roboticist should learn the basics of a few type of technologies and components before embarking himself in the design and construction of his own robot. I would say that the main areas one should be familiar with are:
- Electric motors: it is important to distinguish the types and to know the basics of operation of the most used motors, e.g. DC brushed, DC brushless, PMSM, steppers, servos, etc. In a typical project, very frequently, one has to select the proper motor for an application and possibly the combination of motor and gearbox. I have published a very useful guide to select an electric motor for a simple robotic application. (https://enriquedelsol.com/2017/11/19/motor-selection-for-robots-i/).
- Motor controllers: the motors need to be powered and controlled with the right hardware, typically based on a H bridge made of transistors. It is important to understand the very basics of motor control to avoid spending a considerable amount of money in unnecessary hardware.
- Sensors: in robotics, it is a must to know the different sensors that can provide positional feedback, such as encoders, resolvers, potentiometers. Some of them will be needed depending on the motor we select for our application. In the simpler scenario of choosing servomotors, position sensors will only be needed as a backup sensing method. Other types of sensors very common are: temperature sensors, force sensors, velocity sensors (tachometers), linear displacement, light sensors, etc. It is very important to measure distance, in order to map the environment or to avoid obstacles. The most common sensors to measure distance are: infrared sensors (relatively inexpensive), ultrasonic sensors (inexpensive as well), lasers and depth cameras. These can measure the distance on a large interval to which they have been calibrated for. For an accurate distance detection, there are switches based on capacitive and inductive technology, very reliable but only available for fixed distances. Other common sensors that are used during the electronic control are current sensors and voltage meters.