Traditional brushed DC motors (commonly used in electric toys and fans) rely on the mechanical sliding contact between stationary brushes and a rotating commutator. This automatically switches the current direction in the rotor windings as they turn, generating continuous electromagnetic torque.
The stator is stationary. In a simple DC motor, it consists of permanent magnets on both sides of the casing (N-pole/red on the left, S-pole/blue on the right), producing a horizontal magnetic field pointing from left to right.
The rotor is the spinning assembly in the center, wrapped with copper wire windings. When energized, these windings act as an electromagnet. Their magnetic poles interact with the stator magnets ("like poles repel, opposite poles attract"), driving the rotor to spin.
Two semi-circular copper commutator segments on the shaft connect to the coil ends. Two stationary carbon brushes on either side connect to the DC power source. As the rotor turns, the commutator segments alternately contact the brushes, automatically reversing the coil's current direction as it passes the vertical dead center to maintain continuous rotation!
In this interactive model, the left side displays the physical cross-section of the brushed DC motor, and the right side shows its connection circuit. When the motor is connected to DC power, current flows through the stationary brushes into the rotor windings, creating electromagnetic torque. The rotor rotates under magnetic attraction. Every time the rotor rotates 180° and passes the center line, the gaps between the commutator segments cross the brushes, reversing the polarity of the current flowing into the windings. This ensures the torque direction remains consistent throughout the rotation.
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| Step | Rotor Angle | Brush (+) Contact | Brush (-) Contact | Electromagnetic Torque | Coil Current |
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The commutator is a set of copper contact segments (two segments in this simplified model) mounted on the rotor shaft, rotating with it. The brushes are stationary carbon blocks held against the commutator by springs. As the rotor turns, the brushes contact different segments in turn. Since one brush is positive and the other is negative, the current direction through the windings reverses mechanically every time the rotor passes the vertical midpoint. This ensures the rotor's magnetic poles always repel and attract the stator magnets in a way that generates continuous clockwise torque.
This is the biggest advantage of brushed DC motors! Commutation is handled entirely mechanically by the brush-commutator interface acting as a physical switch. Simply applying DC voltage to the terminals makes the motor run continuously. It requires no microcontrollers (MCUs), driver chips (MOSFETs), or rotor position sensing algorithms, making the system extremely cheap and simple.
There are three main disadvantages:
• Brush wear and short lifespan: The constant sliding friction between the brushes and commutator wears the carbon brushes down over time, requiring regular maintenance or replacement.
• Arcing and electromagnetic interference (EMI): As the brushes switch contacts, electrical arcing occurs due to coil inductance. This creates tiny sparks (unsuited for explosive environments) and generates significant electrical noise that interferes with nearby electronics.
• Poor thermal dissipation and efficiency: The heat-generating windings are on the spinning rotor, making it difficult to transfer heat directly to the outer casing, which limits the motor's power density.
The fundamental principle is identical. However, to prevent the motor from getting stuck at the 90° vertical dead center (where it cannot start from a standstill), practical toy motors typically use a 3-pole rotor (three core teeth and three commutator segments). This design ensures that at least two phases are always energized at any given angle, enabling the motor to self-start reliably from any static position and run with smoother, more even torque.