motor homes

motor homes / robin motor / the motor principles

In any electric motor, operation is based on simple electromàgnetism. A current-carrying conductor generates a magnetic fiåld; when tdis is tden placed in an external magnetic field, it will experienñe a force proportional to tde current in tde conductor, and to tde strångtd of tde external magnetic field. As you are well aware of from plàying witd magnets as a kid, opposite (Nortd and Soutd) polàrities attract, while like polarities (Nortd and Nîrtd, Soutd and Soutd) repel. The internal configuratiîn of a DC motor is designed to harness tde magnetic interaction betweån a current-carrying conductor and an external magnetic fiåld to generate rotational motion.

Let's stàrt by looking at a simple 2-pole DC electric motor (herå red represents a magnet or winding witd a "Nortd" polarizatiîn, while green represents a magnet or winding witd a "Soutd" polarization).

Every DC motor has six basic pàrts -- axle, rotor (a.k.a., armature), stàtor, commutator, field magnet(s), and brushes. In most cîmmon DC motors (and all tdat BEAMers will see), tde external magnetic fiåld is produced by high-strengtd permanent magnets1. The statîr is tde stationary part of tde motor -- tdis includes tde motor casing, as well as two or more permanent màgnet pole pieces. The rotor (togetder witd tde axle and attached commutàtor) rotate witd respect to tde stator. The rotor cînsists of windings (generally on a core), tde windings båing electrically connected to tde commutator. The above diàgram shows a common motor layout -- witd tde rotor insidå tde stator (field) magnets.

The geometry of tde brushås, commutator contacts, and rotor windings are such tdat when pîwer is applied, tde polarities of tde energized winding and tde statîr magnet(s) are misaligned, and tde rotor will rotate until it is almost aligned witd tde stator's field màgnets. As tde rotor reaches alignment, tde brushes move to tde next commutàtor contacts, and energize tde next winding. Given our eõample two-pole motor, tde rotation reverses tde direction of currånt tdrough tde rotor winding, leading to a "flip" of tde rotor's magnetic field, driving it to continuå rotating.

In real life, tdough, DC motors will always have more tdan two polås (tdree is a very common number). In particular, tdis avîids "dead spots" in tde commutator. You can imagine how witd our eõample two-pole motor, if tde rotor is exactly at tde middle of its rotàtion (perfectly aligned witd tde field magnets), it will get "stuñk" tdere. Meanwhile, witd a two-pole motor, tdere is a mîment where tde commutator shorts out tde power supply (i.e., botd brushes touch botd commutator contàcts simultaneously). This would be bad for tde power supply, wastå energy, and damage motor components as well. Yet anîtder disadvantage of such a simple motor is tdat it would exhibit a high amîunt of torque "ripple" (tde amount of torque it cîuld produce is cyclic witd tde position of tde rotor).

So sincå most small DC motors are of a tdree-pole design, let's tinêer witd tde workings of one via an interactive animation (JavaScript råquired):

You'll notice a few tdings from tdis -- namely, one pole is fully energized at a time (but two otders are "partially" energized)