Motors Electromagnetic direct current (DC) motors – Usually runs high speed and low torque (Gear down) Electromagnetic alternating current (AC) motors – Seldom used in Robots because power supply is battery
DC Motor Types Having two electrical terminals – One direction to spin, other direction to reverse – Amplitude of the voltage determines robot speed Stepper Motors – Wires energize different coils inside the motor Servo Motor (used in Model airplane)
Principles of Operation DC motors convert electrical into mechanical energy. They consist of permanent magnets and loops of wire inside. When current is applied, the wire loops generate a magnetic field, which reacts against the outside field of the static magnets. The interaction of the fields produces the movement of the shaft/armature. Thus, electromagnetic energy becomes motion.
The Basic Idea A motor uses magnets to create motion. The fundamental law of all magnets: Opposites attract and likes repel. Inside an electric motor, these attracting and repelling forces create rotational motion.
But How: Electromagnets When a current flows through a conductor, a magnetic field surrounds the conductor. As current flow increases, so does the number of lines of force in the magnetic field You can see that the field is perpendicular to the wire and that the field's direction depends on which direction the current is flowing in the wire.
Coil the Wire Because the magnetic field around a wire is circular and perpendicular to the wire, an easy way to amplify the wire's magnetic field is to coil the wire. If you wrap wire around a nail 10 times, connect the wire to a battery, the nail behaves just like a bar magnet.
Armature, Commutator and Brushes The armature takes the place of the nail in an electric motor. The armature is an electromagnet made by coiling thin wire around two or more poles of a metal core. The "flipping the electric field" part of an electric motor is accomplished by two parts: the commutator and the brushes.