Relay: control larger power
Transistors:
Screw terminal: will not be conductive, safer
The current will go to relay
Solenoids: motor, a set of magnetic, when the circuit is energized, the magnetic will be closed, vice versa, it will release
DC motor: two side magnetic, rotating magnetic, ring mechanism, ca n not have precise control
Stepper Motor: can control precisely, direction, angle, very powerful, large
Servo motor: there is a DC Motor inside, Cooper union building behind has large stepper motor