Claire Fredrickson
Motor Design, Construction, Troubleshooting, and Testing Lab Report 1.
Motor Theory: How our Motor Works
An el ectric motor is all about magnets and magnetism: A motor uses magnets to create motion. The fundamental law of all magnets states: Opposites attract and likes repel. So if you have two bar magnets with their ends marked "north" and "south," then the north end of one magnet will attract the south end of the other. On the other hand, the north end of one magnet will repel the north end of the other and similarly, south will repel south. In an electric motor, these attracting and repelling forces create a magnetic field which can be used to drive an electric motor.
To understand how an electric motor works, the key is to understand how the electromagnet works. An electromagnet is the basis of an electric motor. You can understand how things work in the motor by observing the field of the electromagnet flips. The flip causes the electromagnet to complete another halfturn of motion. You flip the magnetic field just by changing the direction of the electrons flowing in the wire. If the field of the electromagnet were flipped at precisely the right moment at the end of each halfturn of motion, the electric motor would spin freely. The "flipping the electric field" part of an electric motor is accomplished by closed electric circuit completed by two parts of the motor: the commutator or armature and the brushes. An electric circuit is a path where electrons from a source flow
.
Current flows in a closed circuit but there will be no current flow in an open circuit. The point where the electrons enter the circuit is called the source of electrons. The exit point of these electrons is called the return, because electrons end up at the source when they complete the path of the electric circuit. The part of an electrical circuit that is between the electrons starting point, and the return point is called the load.
In an electric motor, an electric circuit is created by using a power source, in this case a power box, to send a current through a stationary brush to a rotating commutator or armature then to a secondary brush on the opposite side of the commutator and back to the power box
completing the circuit. The commutator is a barrel with one end of the wire coiled on top of the barrel and the other end of the wire coiled on the bottom of the barrel. The center section of the wire is wound to form the electromagnetic core. Current transferred to one end of the wire on one half of the barrel causes the current to flow through the electromagnetic core in one direct resulting in a half turn or flip, then the current is transferred to the other end of the wire on the other half of the barrel causing the current to flow in the opposite direction resulting in another half turn or flip, thus creating continuous rotation and converting electrical power into mechanical power or torque.
Electromagnetic induction is the production of electromotive forces across the conductor when it is exposed to a varying magnetic field described by Faraday's law dφb/dt.
Electric current is the flow of electric charge, in an electric circuit charge is often carried by moving electrons in a wire. Torque is a twisting force that tends to cause rotation. The load and torque are measured in Ncm. If the motor output torque is greater than the load then the motor will spin faster. Resistance is the ratio of the voltage applied to the electric current as described in Ohms law I=V/R. Polarity is the property of having poles like the magnets have north and south poles. Force= mg, force strength or energy as an attribute of physical action or movement.
Back Emf is the counterelectromotive force. It is the voltage, or electromotive force, that pushes against the current which induces it. Power is a supply with mechanical or electrical energy.
P=vi, Pin= Es x i, Pr= Vr x i,
