Different motors:

DC motor: https://www.youtube.com/watch?v=LAtPHANEfQo

coil in magnetic field induced with current that flips when the motor turns (brushes connected to ends of the coils): 
add coils to make smoother motion (usually encased in  steel)
Magnetic current induced from other coils: 
-in parallel (shunt motor): good start, drops with load
-in series (series motor): low starting speed, but won't slow down
Also produce Back-EMF: voltage appears in opposite direction. Used by generators: they tap into this voltage
This makes heat: need a fan...

https://www.youtube.com/watch?v=0PDRJKz-mqE&feature=iv&src_vid=LAtPHANEfQo&annotation_id=annotation_145077053
Universal motor: special DC series motor that can also run on AC:
The magnetic field also reverts with AC, so the rotation induced is always in same direction
But need some extra: Eddy current is heavy, so need laminated layers / very resistant brush contact to the coils

https://www.youtube.com/watch?v=bCEiOnuODac
Brushless DC motors: brushes are noisy, wear out and make sparks
Close to Stepper motor (donkey following carrot) also coil behind can be energized in opposite polarity (BLDC)

Description of parts: https://www.youtube.com/watch?v=0hWe1oF5UBg
DC motor: axle, coil (copper wire), armature (on coil), commutator (split rings on axle, brushes (against commutator), 2 magnets inducing magnetic field, and cover/casting
Hooking up: right wire connection: clockwise rotation; switch up, anticlockwise

Geared DC motor: gearing attached to axle, slows down and more resistance offered. Rotation is in rotations of the shaft per minute (RPM)

Brushless DC motor: base, rotor with min 4 coils around, armature, magnets

Stepper motor: brushless DC motor dividing a rotation in number of steps. 3 classes:
- permanent magnet
- variable reluctance
- hybrid
1) Magnet rotates within coils that are energized as it goes around . increase resolution with increased number of coils 
2) Rotor has teeth that when aligned with one coil are misaligned with the next. Increase resolution with number of teeth and/or coils
3) Superimposed rotors with teeth and slight misalignment, one + other -. Coils around have teeth and use same principle

Servo motor: 
an actuator with precise control on angle; 
motor with sensor for feedback
3 wires: VCC, ground, and PWM signal; 
requires controller

H-bridge: "an electronic circuit that enables a voltage to be applied across a load in either direction. These circuits are often used in robotics and other applications to allow DC motors to run forwards and backwards.""