A gebürsteter Gleichstrommotor converts direct-current electrical energy into rotary mechanical motion. It uses stationary brushes and a segmented commutator to switch current through the rotating armature windings, allowing the motor to produce continuous torque without electronic commutation.

Its operation is simple to understand, but its actual performance depends on the interaction between supply voltage, back electromotive force, winding resistance, armature current and mechanical load. At startup or stall, back EMF is absent and the current can rise far above the normal running value. During continuous operation, winding temperature, brush wear, duty cycle and heat dissipation determine whether the motor can operate reliably.

This article explains the construction and working principle of a brushed DC motor, then examines the electrical, thermal and mechanical limits that matter in practical applications.

Wichtigste Erkenntnisse

• Brushes and a segmented commutator mechanically switch the armature current, allowing the rotor to produce continuous torque.
• Motor speed depends mainly on applied voltage, back EMF and load, while torque is approximately proportional to armature current.
• At startup or stall, back EMF is near zero, so current can be several times higher than the normal running current.
• Continuous torque is limited by winding temperature and heat dissipation; stall torque is a short-term limit, not a continuous rating.
• Brush life depends on current, speed, temperature, duty cycle, commutation quality and the frequency of starting and reversing.

What is A Brushed DC Motor？

A brushed DC motor is an electromechanical device that converts DC electrical power into rotary motion through mechanical commutation. In the permanent-magnet designs commonly used for small motors, magnets in the stator create a stationary magnetic field, while current flows through the brushes and commutator into the rotating armature windings.

The interaction between the armature current and the stator magnetic field produces torque. As the rotor turns, the segmented commutator changes the electrical connection to the armature windings at the appropriate rotor position, helping the motor continue rotating in the same direction. A basic brushed motor can therefore operate from a suitable DC supply without requiring electronic commutation.

Brushed DC Motor Structure

Most small permanent-magnet brushed DC motors can be explained through four functional assemblies: the stator, rotor or armature, commutator and brushes. A complete motor also includes the shaft, bearings, housing and end cap, which affect alignment, vibration, mechanical load capacity and service life.

Stator

The stator provides the stationary magnetic field. In a permanent-magnet DC motor, magnets are fixed inside the steel housing, which also forms part of the magnetic return path. Wound-field motors use energized field windings instead of permanent magnets.

Magnet strength, air-gap uniformity and magnet alignment affect the torque constant and the current required at a given load. An uneven air gap can also contribute to noise, vibration and inconsistent performance between samples.

Rotor

The rotor is the rotating assembly and normally includes the shaft, armature windings, commutator and, in a conventional design, a laminated iron core. Current flowing through the windings interacts with the stator field to produce torque.

The winding design determines resistance, inductance and the motor’s torque and speed constants. In production, winding consistency, insulation quality, commutator connection and rotor balance directly affect current, temperature rise, vibration and reliability.

Windings/Coils: Copper wires wound around an iron core. The number of coils and their winding configuration determine the motor’s performance.

Iron Core: The coils are typically wound on a laminated iron core, which not only provides sturdy support for the coils but also helps concentrate the magnetic field and dissipate heat.

Kommutator

The commutator is a cylindrical assembly of mutually insulated conductive segments mounted on the rotor shaft. Each segment is connected to part of the armature winding.

As the rotor turns, the brushes transfer contact from one segment to the next, changing the current path through the windings. This process is known as mechanical commutation. Segment geometry, surface finish, concentricity and commutation timing influence sparking, electrical noise, torque ripple and brush wear.

Pinsel

The brushes are stationary electrical contacts that transfer current from the external circuit to the rotating commutator. Depending on motor size, current and operating conditions, they may use carbon-graphite, metal-graphite or precious-metal contact systems.

Brush spring force must maintain stable contact without producing excessive friction. Insufficient contact pressure can cause bouncing and arcing, while excessive pressure increases mechanical loss and wear. Brush material therefore cannot be evaluated independently of current, speed, PWM drive conditions and commutator design.

Mechanical commutation is the main structural difference between brushed and brushless motors. For a concise system-level comparison, see Brushless DC vs Brushed Motor: Making the Right Choice.

For available motor sizes, voltages and winding options, visit our brushed DC motor product range.

How Does a Brushed DC Motor Work?

When DC voltage is applied to the motor terminals, current flows through one brush, across the commutator, through the selected armature windings and back through the opposite brush. The energized windings create a magnetic field that interacts with the stator field and produces torque on the rotor.

The brushes and commutator then switch the current path mechanically as the rotor changes position. This keeps the electromagnetic torque acting in the required rotational direction. Unlike a brushless motor, the switching sequence does not require an external rotor-position sensor or electronic commutation circuit.

The Mechanical Commutation Cycle

1. Current enters the armature. The brushes contact specific commutator segments and energize the connected windings.
2. Electromagnetic torque rotates the rotor. The magnetic field produced by the armature interacts with the stationary stator field.
3. The current path changes. As the rotor passes through the commutation region, the brushes move from one commutator segment to the next, changing the current direction in the relevant winding.
4. Torque continues in the same rotational direction. The cycle repeats as additional windings are energized and commutated.

Real motors normally use several coils and commutator segments rather than a single coil. More winding sections can reduce torque variation and help the motor start from different rotor positions.

The brushes do not actively measure rotor position. Commutation timing is determined by the mechanical relationship between the brushes, commutator segments and magnetic neutral region. Incorrect brush alignment, commutator eccentricity, surface contamination or excessive current during switching can increase arcing, heat, electrical noise and brush wear.

What Determines Brushed DC Motor Speed, Torque, and Current?

A brushed DC motor does not have one fixed speed or current. Its operating point is established by the supply voltage, winding resistance, back electromotive force, motor constants and mechanical load.

Under steady-state operation, the main electrical relationships can be simplified as:

V = E + I × R + Vbrush

E = kE × ω

T = kT × I

Where:

• V is the voltage measured at the motor terminals;
• E is the back EMF generated by rotation;
• I is the armature current;
• R is the armature winding resistance;
• Vbrush represents the voltage drop across the brush and commutator contacts;
• ω is the rotational speed;
• kE is the back-EMF constant;
• kT is the torque constant.

The torque produced by the motor is approximately proportional to armature current, while back EMF increases with rotational speed. These relationships are also explained in maxon’s motor data reference.

What Happens When the Load Changes?

• At light load, the motor accelerates, back EMF increases and armature current falls to the level needed to overcome friction and the external load.
• When the load increases, speed decreases and back EMF falls. This allows more current to flow, producing additional torque.
• At startup or stall, rotational speed and back EMF are approximately zero. Current is then limited mainly by winding resistance, brush contact drop, wiring and driver impedance.

Winding inductance prevents current from rising instantaneously, but this electrical transient is usually brief in a small motor. If the rotor cannot accelerate, the current approaches the stall-current level:

Istall ≈ (V − Vbrush) / R

Nidec’s explanation of DC motor speed and counter-electromotive force shows the same sequence: higher load reduces speed and back EMF, causing current and torque to increase until a new operating balance is reached.

Practical Engineering Implications

Do not use no-load speed alone to predict performance under load. Two motors with the same rated voltage and external dimensions may use different windings and therefore have different resistance, speed constants, current and torque characteristics.

The driver, power supply, connectors and wiring must tolerate startup and transient current without excessive voltage drop. Actual voltage should be checked at the motor terminals while the motor is loaded, rather than assumed from the power-supply label.

Stall torque represents a zero-speed limit and should not be treated as a continuous operating point. For a detailed explanation, see Nenndrehmoment vs. Haltemoment: Welchen Wert sollten Ingenieure verwenden?.

Types of Brushed DC Motors

Brushed DC motors can be classified based on the stator excitation method and the rotor structure.

Classification by Stator Excitation Method

Permanent Magnet (PMDC) Motors

The stator magnetic field is generated by permanent magnets. This is the most common type for small applications, known for its compact structure, reliability, and energy efficiency, as the stator field does not consume electrical power.

Wound-Field Motors

The stator magnetic field is generated by electromagnets (field coils). Based on how the field windings are connected to the armature windings, they are divided into three main subtypes:

• Series-Wound: The field coil is connected in series with the armature. This motor provides very high starting torque, but its speed varies greatly with the load. It is ideal for heavy-duty applications like cranes and winches.
• Shunt-Wound: The field coil is connected in parallel (shunt) with the armature. This motor has good speed regulation, running at a relatively constant speed regardless of load changes.
• Compound-Wound: Combines the characteristics of both series and shunt windings. It offers both high starting torque and good speed stability, suitable for applications requiring both.

Classification by Rotor Structure

Based on the classification by rotor structure, brushed DC motors are categorized into two types: iron-core motors and coreless motors.

Iron-core Motors

This is the standard design, where the coils are wound on a laminated iron core. The structure is robust and produces high torque, but the mass of the iron core results in high rotational inertia and can cause “cogging effect” (a slight jerkiness) at low speeds.

Coreless Motors

The rotor winding is a self-supporting, hollow structure, and the stator magnet is usually located inside the hollow rotor. This design has extremely low rotational inertia, allowing for extremely fast acceleration and deceleration. It is also more efficient (no iron losses) and generates less electromagnetic interference. It is an ideal choice for high-performance applications such as robotics and medical devices.

Table 1: Brushed DC Motor Type Comparison (by Stator Excitation)

Table 2: Coreless Brushed Motor vs. Cored Brushed Motor Performance Comparison

Brushed Electric Motor Controls

For simple unidirectional operation, a brushed motor may not even require any external controller—just a DC power source and a switch. This is a major advantage. Below we discuss the speed control and direction control of brushed motors.

How to Control Speed of Brushed DC Motor？

There are two methods for motor speed control: variable voltage and Pulse Width Modulation (PWM).

Variable Voltage: This is the simplest method. Motor speed is proportional to the applied voltage; lowering the voltage lowers the speed. However, using a resistive divider to lower the voltage is very inefficient.

Pulse Width Modulation (PWM): This is the modern, efficient control method. By rapidly switching the voltage on and off at a very high frequency, the speed is controlled by changing the ratio of the “ON” time to the total time (i.e., the duty cycle), which effectively changes the “average” voltage applied to the motor. This method is highly efficient because the switching device (transistor) is either fully on or fully off, minimizing energy loss.

How to Reverse Brushed Electric Motor Direction？

Motor direction control can be achieved in two ways: reversing polarity or using an H-Bridge circuit

• Reversing Polarity: Simply reversing the polarity of the DC voltage applied to the brushes changes the motor’s direction of rotation.
• H-Bridge Circuit: In electronic control, this is typically achieved through a circuit consisting of four transistors (usually MOSFETs), named for its resemblance to the letter “H.” By switching the two diagonal pairs of transistors (e.g., Q1 and Q4, or Q2 and Q3), the current can be controlled to flow through the motor in either direction, enabling both forward and reverse control.

DC Brushless VS Brushed Motor

The core of the brushed motor is the physical brush-commutator system. The Brushless DC (BLDC) motor, however, is a “flipped” design: the permanent magnets are on the rotor, and the electromagnetic coils are on the stator.

In a bürstenloser Gleichstrommotor, there are no brushes.

The switching (commutation) of the current in a brushless motor is performed by an external electronic circuit—the Electronic Speed Controller (ESC). The ESC uses transistors to energize the stator coils in a precise sequence, creating a rotating magnetic field that “drags” the permanent magnet rotor to spin.

If you want a comprehensive comparison between Brushless DC Motors (BLDC) and Brushed DC Motors, please click here to read this article：Brushless DC Motors Explained: What They Are, How They Work

Table 3: Brushed DC Motor vs. Brushless DC Motor

Applications of Brushed DC Motors

Despite the challenges from new technologies, the brushed DC motor still holds its ground in many fields due to its unique advantages.

Low-Cost Consumer Goods

Due to their low cost and simple structure, brushed motors are ubiquitous in applications where performance and lifespan are not critical, such as inexpensive toys, electric toothbrushes, fans, and small kitchen appliances.

Automotive Systems

They are widely used for intermittent functions in cars, such as electric windows, power seats, windshield wipers, and starter motors.

Heavy Industry

Their rugged and durable nature is still favored in some high-power, high-torque applications, such as cranes, rolling mills, and paper machines.

Robotics and Automation

In robotics, especially where high starting torque is needed, brushed motors still find use. High-performance coreless brushed motors are used in fields like humanoid robots and medical prosthetics due to their fast response capability.

Power Tools

Although the power tool industry is gradually shifting to brushless motors, brushed motors are still widely used in many corded and cordless tools.

All this suggests that the value of the brushed DC motor has shifted from purely performance-based considerations to an economic and engineering trade-off. In almost all performance metrics, the brushless motor is superior.

However, brushed motors are still being mass-produced and used. The fundamental reason is that for a massive number of applications, the combination of the brushed motor’s “good enough” performance and its low cost makes it the optimal engineering choice.

A toy car does not need 90% efficiency or a lifespan of tens of thousands of hours. The enduring success of the brushed motor is a classic lesson in pragmatic engineering economics.

Fazit

The brushed DC motor defined an era with its elegant mechanical commutation, simple control, high starting torque, and low cost. While newer technologies like the brushless motor have surpassed it in performance, the brushed motor’s unparalleled simplicity and cost-effectiveness ensure it firmly holds its place in the engineering world.

Today, innovations like integrating Artificial Intelligence (AI) and the Internet of Things (IoT) for predictive maintenance in industrial settings are further extending the lifespan and practicality of these classic machines. Therefore, the brushed DC motor should not be viewed as an outdated relic but as a foundational technology. Its basic principles remain relevant today, and its design is itself a masterclass in clever electromechanical problem-solving.

Frequently Asked Questions (FAQ)

Q1: What exactly is a Brushed DC Motor?

A Brushed DC motor is a device that converts DC electrical energy into mechanical energy. It gets its name from its core structure—the “brushes” and the “commutator”—which together are responsible for periodically changing the direction of the current flowing through the rotor coils to produce continuous rotational torque.

Q2: What are the four main components of a Brushed DC Motor?

Stator: The stationary part that produces the fixed magnetic field (usually permanent magnets or field windings).

Rotor/Armature: The rotating part, consisting of winding coils.

Commutator: A mechanical switch mounted on the rotor that periodically reverses the current direction.

Brushes: Stationary conductive contacts that connect the external power source to the rotating commutator.

Q3: What is the main difference between Cored and Coreless motors?

Coreless/Hollow-Cup Motors: Have extremely low rotational inertia, fast response speed, high efficiency, and excellent low-speed smoothness (no cogging torque). However, they have relatively smaller torque and poorer heat dissipation. Suitable for high-precision, fast-response applications (e.g., medical devices, drones).

Cored Motors: Have high rotational inertia and can generate high torque. They have a robust structure and low cost. Suitable for general industrial and household appliance applications.

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Tsinglin Motor’s Relevant Brushed DC Motor Series