MODULE 8 — Special Purpose Machines
8.1 Stepper Motor
Step Angle ($\theta_s$)
$$ \theta_s = \frac{360^\circ}{m \times N_r} $$
Alternative Form
$$ \theta_s = 360^\circ \times \frac{N_s - N_r}{N_s \times N_r}
$$
Stepping Rate ($f$)
$$ n = \frac{\theta_s \times f}{360} \quad \text{(RPS)} $$
8.2 Brushless DC (BLDC) Motor
- Commutation: Electronic (Inverter)
- Rotor: Permanent Magnets
- Stator: 3-Phase Windings
- Sensors: Hall-effect (detects rotor position)
8.3 Switched Reluctance Motor (SRM)
$$ T = \frac{1}{2} i^2 \frac{dL}{d\theta} $$
Torque is produced by the tendency of the rotor to align with the stator poles, maximizing inductance ($L$). No rotor windings or magnets.