As far as I know:

DC motors draw maximum current, and produce maximum shaft torque, at minimum speed. Current and torque is proportional to applied voltage. More voltage = more current.

Field winding(s) control strength of rotor's magnetic field, armature windings control strength of the static field. Torque is produced by the angle between the amature and rotor magnetic fields acting on the shaft. The commutator 're-aligns' the rotor field so that it can continue to produce torque, otherwise the rotor would turn through 180 degrees until the fields aligned, and then stop. Not too useful without commutation.

DC motors have series, shunt or compound field windings. Shunt or compound are most common. Series-wound have a nasty habit of trying to overspeed to destruction if the field current is too low.

Back EMF drops the armature current as rotational speed increases.

AC induction motors work differently. The armature windings produce a rotating magnetic field.

The rotating field induces current in the field windings, which produces a magnetic field. Again, the angle between fields produces torque, but no commutator is required because the field is rotating. The rotor fields 'chases' but never 'catches' the armature field.

AC inductons motors also draw maximum current at minimum speed (Locked Rotor) and back EMF reduces current when they are spinning.

Within their design range, lower voltage will raise current to maintain torque (power). When stalled, AC induction motors do not produce much torque, so they have a second set of rotor windings, or sometimes a second armature winding with a phase shift, produced by a capacitor, to help starting.

Many household AC induction motors are either "capacitor-start" or "capacitor-run" design.


For further reading and enjoyment,

http://www.engin.umich.edu/labs/csdl/ME350/motors/

Best Regards,
Jim