What is the difference between brushed and brushless motors?

Brushed motors use mechanical carbon brushes to alternate current, leading to friction and wear over time. brushless-bldc motors use electronic controllers to switch current across stationary stator coils, delivering superior efficiency.

How does back-EMF affect motor speed?

As the rotor spins, its coils generate a counter-electromotive voltage ( back-emf ) opposing the supply voltage. As speed increases, back-EMF rises until it balances supply voltage, establishing the motor maximum unloaded RPM.

When should I choose a stepper motor over a servo?

Choose a stepper-motor for open-loop precision positioning at low speeds like 3D printers. Choose a closed-loop servo-motor when high speed, smooth continuous torque, and dynamic error correction are needed.

Build / Mechanics / Motors

Electric Motors 101

A primer on DC and AC electric motors, electromagnetic induction, torque curves, and motor control circuits.

TL;DR

Generate magnetic rotational force using stator-coils and rotor magnets.
Control motor speed dynamically using pulse width modulation pwm-signals.
Calculate mechanical power output from torque multiplied by angular speed.

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Motor Operating Principles
Motor Typologies
Drive Electronics and Control

Motor Operating Principles

Lorentz Force Law

Calculates electromagnetic force exerted on current-carrying wire in magnetic field.

force = current * wire_length * magnetic_flux

Torque and Power

Quantifies rotational torque and converted mechanical shaft horsepower.

power_watts = torque_nm * angular_velocity_rad_s

Motor Constant (Kv)

Specifies rotational RPM generated per volt of applied unloaded voltage.

rpm = applied_voltage * motor_kv_rating

Stall Current

Maximum current draw when rotor is completely locked at zero RPM.

stall_current = supply_voltage / winding_resistance

Motor Typologies

Brushless DC (BLDC)

Permanent magnet rotor driven by three-phase electronic commutation.

commutation: 3_phase_trapezoidal_or_sinusoidal

Stepper Motor

Divides full 360-degree rotation into discrete fractional step angles.

step_angle: 1.8_deg // 200 full steps per revolution

AC Induction Motor

Stator magnetic field induces current into squirrel cage rotor conductors.

slip: synchronous_speed - actual_rotor_speed

Drive Electronics and Control

H-Bridge Circuit

Arrangement of four transistors enabling bidirectional motor rotation.

state: [Q1_Q4_forward, Q2_Q3_reverse, all_off]

PWM Speed Control

Varies average voltage delivered to windings by modulating duty cycle.

effective_v = supply_v * (duty_cycle_ms / period_ms)

Hall Effect Sensors

Detects rotor magnetic pole positions to coordinate phase switching.

feedback: 3_digital_sensors_spaced_120_deg

Tips

Select a brushless-bldc motor whenever high efficiency, long bearing life, and low maintenance are required.
Add a flyback freewheeling-diode across DC motor terminals to suppress destructive inductive voltage spikes.

Warnings

Never stall an electric motor under full voltage to prevent rapid thermal winding insulation-burnout.
Avoid exceeding rated continuous current to maintain neodymium rotor magnet demagnetization limits.

In Practice

Calculate throttle duty cycle from desired motor RPM and voltage.

Measure input battery pack supply voltage.
Query motor Kv rating from manufacturer specification.
Calculate theoretical maximum unloaded rotation speed.
Output corresponding PWM duty cycle percentage to ESC.

def compute_esc_throttle(target_rpm, supply_v, motor_kv):
    max_rpm = supply_v * motor_kv
    if target_rpm >= max_rpm:
        return 1.0  # 100% duty cycle
    throttle = target_rpm / max_rpm
    return round(throttle, 3)