There is no basic difference between the construction of DC motors and generators. Rotating machines of this type must have the following basic features.
1. A magnetic field system
2. A system of conductors
3. Provision for relative movement between the field and the conductors
In most DC machines the magnetic field is set up by the stationary part of the machine, which is called the field system. The commutator and the conductors which form the armature winding, are mounted on the rotating part of the machine.
The body of the machine is a hollow cylinder of cast steel called the yoke. Which forms the basis for construction of the machine and is part of the magnetic circuit. Fixed pole pieces made of solid steel or iron are fixed inside the yoke.
Each pole has one or more field windings placed over it to produce a magnetic field. There is always an even number of poles.
Then there are the armature windings of the DC machine which are often very complex, there are two basic types.
1. Wave windings – these tend to be high voltage, low current windings, and always have two conducting paths in parallel.
2. Lap windings – these tend to be low voltage high current windings, and have as man conducting paths in parallel as there are poles.
The ends of the winding are brought out of the slots at one end, where they are connected to the lugs on the commutator by welding or soldering. A typical commutator will be made up of many hard drawn copper segments each one insulated from the other with mica.
The completed armature is mounted on bearings, often supported by end plates mounted on the yoke. The carbon brushes are mounted so that the pressure exerted by them on the commutator can be adjusted, and so that the pressure will remain reasonably constant as the brushes wear.
Below is a picture of a DC motor with a spilt yoke, showing much of the above descriptions.