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            Yoke (outer frame)
        +---------------------------+
        |   N pole core + field coil |
        |      \_pole shoe_/         |
        |    .-----------------.     |
        |   /  armature core    \    |
   Yoke |  |  with slots and     |   | Yoke
        |  |  conductors (x / .) |   |
        |   \   [commutator]    /    |
        |    '------|shaft|----'     |
        |      /  pole shoe  \       |
        |   S pole core + field coil |
        +---------------------------+
   Brushes (carbon) press on the commutator; bearings support the shaft.

Parts and functions:

PartFunction
Yoke (frame)Outer cast-iron/steel frame; gives mechanical support and protection, and carries the magnetic flux (return path) between poles.
Poles and pole shoesPole core carries the field winding; pole shoe spreads the flux uniformly in the air gap and supports the field coils.
Field windingCopper coils on the poles; when excited by DC they produce the main magnetic flux.
Armature coreLaminated silicon-steel cylinder with slots; houses armature conductors and provides low-reluctance path; laminations reduce eddy-current loss.
Armature windingCopper conductors in slots; carry current and experience force (F = BIl) to produce torque.
CommutatorCopper segments insulated by mica; reverses current in armature conductors as they pass from one pole to the next so that torque is unidirectional; connects armature to external circuit.
BrushesCarbon/graphite blocks pressed on the commutator by springs; conduct current between external supply and rotating commutator.
Shaft and bearingsShaft transmits mechanical power to the load; bearings give friction-free rotation.

Types of DC motors (according to field excitation):

  1. Separately excited DC motor — field winding supplied from an independent DC source.
  2. Self-excited DC motors:
    • Shunt motor — field winding (many turns of thin wire) in parallel with armature; nearly constant speed (lathes, fans, blowers).
    • Series motor — field winding (few turns of thick wire) in series with armature; very high starting torque (traction, cranes, hoists); never started on no load.
    • Compound motor — both shunt and series fields: long-shunt or short-shunt; cumulative or differential compound (presses, shears, rolling mills).
  3. Permanent magnet DC (PMDC) motor — field produced by permanent magnets (toys, wipers, small appliances).
Doubtly AI · 25 Oct 2026 AI-verified · Oct 2026 Report
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