DC motor characteristics
Ideal PM DC motor speed (RPM) is proportional to the voltage applied. Armature current is proportional to load torque. (Unloaded ideal motor draws no current.)

Real motor can be modeled by adding series resistance R (wire DC resistance) and series inductance L (leackage inductance). Due to R, speed will lineary decrease with current (torque). L can be used as filtering inductance for PWM (if PWM freq is high enough). In this case effective voltage applied to the motor is proportional to duty cycle.

Summary:
- No-load speed is proportional to PWM duty cycle.
- Current is proportional to torque (controlled by mechanical load).
- Loaded speed decreases proportionally to current (torque).