A direct-current motor is a device for converting dc electrical energy into rotating mechanical energy.
All motors have several basic characteristics in common. They include:
Basic Functionality
The starter motor converts electrical energy to mechanical energy and is mounted on the cylinder block in a position to engage a ring gear on the engine flywheel.
Starting is usually accomplished by the operator activating a starter switch as part of ignition key operation. This allows a relatively small current to flow to a starter solenoid relay and operate a plunger attached to a drive pinion engagement lever.
Plunger movement engages the drive pinion with the ring gear and closes a set of heavy duty contacts, allowing a large current to flow from the battery to the starter motor, rotating the armature and drive pinion, and causing the crankshaft to spin.
When the engine starts and is able to run on its own, the operator usually releases the key and this withdraws the pinion from the ring gear and brings the armature to a halt.
Principle of Operation
The basic principle that drives the starter motor, which is a DC motor, is Faraday’s Law; which states that electrical current is produced when there is relative motion between a conductor and magnetic field. Of course the law is stated for a generator, however the opposite is also true, motion is produced when a current carrying wire is in the presence of magnetic field. The motion is determined by two factors, the direction of the current and the direction of the magnetic field.
The right-hand rule for motors is used when determining the direction of the motion. To aide in understanding this principle:
If the forefinger is pointed in the direction of magnetic flux (north to south) and the middle finger is pointed in the direction of current flow in the conductor, the thumb will point in the direction the conductor will move.
The opposite is true for a generator. This can be confusing but if you remember the above sequence, you won't go wrong.
If the wire is moved up and down in the magnetic flux then a current is generated. The magnetic flux is provided by the by the housing, or the stator. The wire is represented by the rotor or armature, which has windings wrapped around it in a specified orientation.
The motor effect
If a current flows in a conductor, and the conductor sits in a magnetic field, then the conductor experiences a force on it in the direction as expect from the right-hand rule. The magnetic field bends the electron beam — thus using a current and a magnetic field to produce a change in motion.
A DC motor needs a commutator change or swap the direction of the current in the coil twice each rotation.
Source: CDX Global & Wikipedia
