Most off-board components are easy to identify what family they belong to. Sometimes you get through-hole components mounted off-board on flying leads. You should look these up in the through-hole section.
Motors[]
Motors are easy to identify as they have a spinning central spindle. When salvaged they often have cogs or pulleys attached to the spindle. Motors come in a few basic categories:
DC Brushed Motors[]
These are your normal DC motor. They usually have 2 connections, and applying a voltage across the pins in different directions makes the motor spin in different directions.
DC Brushless Motors[]
These are more complex than the normal DC motor. They will usually only spin in one direction when power is applied. They operate by means of multiple coils which are switched on in different combinations by internal electronics.
Stepper Motor[]
Stepper motors have multiple connections. When power is applied to certain combinations of connections the spindle turns a small amount. They come in two basic types:
Bipolar Stepper[]
These are the harder of the stepper motors to drive. Each coil within the motor is a separate entity, and to change the polarity of the coil you will have to change the polarity of the drive current. You can identify these with a multimeter because there is no common connection anywhere.
Unipolar Stepper[]
These are much easier to drive than bipolar steppers. The coils are grouped into pairs with a common centre tap. Alternating between the two sides of the coil anternates the polarity of the drive. The commons from each coil are sometimes all tied together into one main common. A multimeter can identify the common pins. From then it's just a matter of working out which order the coils should be activated in.
Servo Motor[]
A servo motor is a precision DC motor coupled with some form of feedback mechanism. Depending on the type of servo, this could be an optical encoder, or a resistive system like a potentiometer.
Transformers and Chokes.[]
Transformers and chokes are both big coils of wire. They are heavy, and typically bulky. A transformer has at least 2 coils of wire and are used to change AC voltages and currents from one level to another. Chokes only have one coil of wire and are used in filtering - typically in switched mode power supplies.