Types of DC Electric Motors: Brushed, Brushless, and Stepper Compared

A DC electric motor is an electromechanical actuator that converts direct current electrical energy into continuous or indexed mechanical rotation via interacting magnetic fields. When you introduce one of these motors into a real circuit, it fundamentally changes the electrical environment: it acts as a highly inductive load that demands massive inrush current (often 5x to 10x its continuous rating), generates reverse voltage (back-EMF) when spinning down, and requires flyback diodes or specialized H-bridge drivers to prevent voltage spikes from frying your microcontroller. Hobbyists frequently confuse Brushless DC (BLDC) motors with AC synchronous motors because they share similar 3-phase stator designs, and they routinely mistake a motor's advertised stall torque (the maximum force before it stops moving) for its continuous rated torque (what it can handle indefinitely without melting).

The Core Types of DC Electric Motors Compared

The term 'DC motor' covers three distinct architectures, each requiring entirely different drive circuitry and offering unique torque curves. Understanding the commutation method—how the current is switched to keep the rotor turning—is the key to selecting the right type.

Worked Example: Sizing a Motor for a 12V Linear Actuator

Let’s look at how motor type changes your electrical and mechanical design when building a 12V motorized heavy-duty curtain track. You need to pull a 40 Newton load at a linear speed of 0.05 meters per second using a spool with a 0.02-meter radius.

1. Calculate Required Mechanical Power:
Required Torque = Force × Radius = 40 N × 0.02 m = 0.8 Nm.
Target Speed = 60 RPM (which is 1 revolution per second, or 6.28 rad/s).
Mechanical Power = Torque × Angular Velocity = 0.8 Nm × 6.28 rad/s = 5.02 Watts.

2. Sizing a Brushed Motor (e.g., RS-775):
A standard 12V 775 brushed motor operates at roughly 75% efficiency at this load. Electrical Power Required = 5.02 W / 0.75 = 6.7 W. At 12V, the continuous current draw is a manageable 0.56A. However, you must size your wiring and fuse for the inrush current. When the 775 motor starts from a dead stop, it acts like a short circuit until back-EMF builds up. Inrush current on a 775 brushed motor can spike to 15A for 200ms. You need a 5A slow-blow fuse and an H-bridge driver like the DRV8871 rated for at least 3.6A continuous to handle the thermal load safely.

3. Sizing a Stepper Motor (e.g., NEMA 23):
Stepper efficiency drops significantly at higher speeds; at 60 RPM, expect about 60% efficiency. Electrical Power = 5.02 W / 0.60 = 8.36 W. But here is the catch: a typical NEMA 23 stepper (like the LDO-57STH76-2804A) is rated at 2.8A per phase. Stepper drivers (like the TMC2209) supply this current constantly to maintain the magnetic field, even when the motor is stalled or moving slowly. Running at 24V, your power supply must be sized for 24V × 2.8A = 78W capacity per motor, and the driver will dissipate massive amounts of heat. For a simple curtain puller, the stepper is a highly inefficient, overheating choice compared to the brushed alternative.

4. Sizing a BLDC (e.g., 2212 Outrunner):
A BLDC motor will achieve 90% efficiency here, requiring only 5.5W of electrical power. It runs cool and draws minimal current. However, you must add a 3-phase Electronic Speed Controller (ESC) and a microcontroller to handle the commutation logic, adding $20-$40 in BOM (Bill of Materials) cost and PCB space. Choose BLDC only if the curtain track runs continuously or battery life (in a solar/off-grid setup) is the primary constraint.

Where You Meet This in Practice

You interact with all three types of DC electric motors daily, often without realizing the distinct engineering trade-offs inside the housings.

• Home Automation & Appliances: Modern ceiling fans and high-end HVAC blowers use BLDC motors for their high efficiency and quiet operation at low RPMs. Conversely, cheap smart locks and motorized deadbolts rely on small brushed coreless DC motors because they only run for two seconds a day, making brush wear irrelevant while keeping the BOM cost under $2.
• 3D Printing & CNC Routing: NEMA 17 stepper motors (typically 1.8° per step, 1.5A to 2.0A) dominate the 3D printing space. They provide open-loop positional accuracy without needing expensive optical encoders. According to Oriental Motor's technical guides, the holding torque of a stepper is highest at zero speed, making them perfect for holding a Z-axis leadscrew against gravity when the printer is idle.
• Automotive Systems: Your car’s windshield wipers and power windows use high-torque brushed DC motors with integrated gearboxes. Meanwhile, the main water coolant pumps in modern EVs and the traction motors themselves are BLDC, managed by complex Texas Instruments gate drivers that handle hundreds of amps and regenerative braking logic.
• Robotics & Gimbals: Camera gimbals use specialized direct-drive BLDC motors with hollow shafts. They operate in a micro-stepping mode to provide ultra-smooth torque ripple correction, relying on IMU (Inertial Measurement Unit) feedback rather than Hall sensors for commutation timing.