DC Motor Basics: How a DC Motor Works – Stator, Rotor, Windings, and Commutation Explained

This video from Engineering Mindset explains the basics of a DC motor. It covers the main components—the stator with permanent magnets, the laminated rotor with windings, the commutator, and brushes—and shows how current through the windings creates magnetic fields that interact with the magnets to produce rotation. The presentation also introduces Fleming's left-hand rule to determine the direction of force and rotation, explains why rotor laminations reduce eddy currents, and describes how the commutator and brushes create the necessary electrical connections to the windings. The video concludes with a review of the rotation mechanism and examples of common applications such as power tools, toy cars, and cooling fans.

Introduction

The video provides a practical exploration of the DC motor, a device that converts electrical energy into mechanical energy. It begins by highlighting typical applications such as power tools, toy cars, and cooling fans, then outlines the basic architecture: a stationary stator housing permanent magnets, and a rotating assembly (the rotor or armature) containing windings. The purpose of the design is to generate a controlled electromagnetic torque that turns the shaft to which gears, fans, or pulleys can be attached.

DC Motor Anatomy

When the casing is opened, two permanent magnets sit inside the stator to form a north and south pole. A central shaft passes through the motor, and the rotor is composed of laminated discs with T-shaped arms. Winding around these arms carries current from the battery, producing an electromagnetic field. The ends of the windings connect to a commutator, a segmented ring that sits around the shaft. The plastic back cover houses the brushes and brush arms, which press against the commutator segments to complete the circuit. This arrangement allows current to flow from the battery, through the terminal, into the windings, and back through the opposite brush to the battery, forming a working electrical path that energizes the coils.

Magnetic Interaction and Rotation

Electrons flowing through the windings generate magnetic fields. By controlling the timing and polarity of these fields, the rotor experiences torques that cause rotation. The permanent magnets establish a static magnetic field through the rotor. The windings are arranged so that, as the current alternates with the commutator, the magnetic forces on opposite sides of the rotor create a rotating motion. The video emphasizes the importance of the coil arrangement: even a single coil can cause jamming if not properly coordinated, so motors typically use at least three coils positioned 120 degrees apart to ensure smooth rotation.

Commutator, Brushes, and Arc Phenomena

The commutator plates connect to the ends of the windings, switching the connection as the rotor turns. The brushes ride against these plates, providing the electrical path. As the rotor moves, the contact points shift, producing small arcs and occasional light flashes where the brushes cross segments. These arcing events, along with mechanical friction, contribute to brush wear and can limit motor life if not managed.

Fleming's Left-Hand Rule and Coil Forces

The video introduces Fleming's left-hand rule as a practical tool to determine the direction of force on a current-carrying conductor in a magnetic field. By aligning the left hand so the second finger points in the direction of conventional current, the first finger in the direction of the magnetic field, and the thumb in the direction of the resulting force, the viewer can predict the motion of each coil. An animated example demonstrates how the left and right sides of a coil experience opposite forces, generating a net rotational torque. A PDF guide is mentioned to help learners memorize the rule and work through examples.

Rotor Design and Eddy Current Reduction

To improve efficiency, the rotor is constructed from laminated discs separated by insulating lacquer. This segmentation minimizes eddy currents that would otherwise circulate within a solid metal armature and waste energy. The thinner the laminations, the smaller the eddy currents, enhancing motor efficiency and reducing heat buildup. The commutator itself is composed of copper plates mounted to the shaft, isolated from one another and from the shaft, with each plate connected to a different winding end.

Operation Cycle and Direction Control

The video walks through a slow-motion view of motor operation, labeling coils and commutator plates (A, B, C) and showing the path of current through different plates. The sequence illustrates how the contact pattern energizes different coils to maintain rotation. It also notes that reversing the power supply reverses the current, which in turn reverses the magnetic forces and the direction of rotation. The explanation highlights how the arrangement of multiple coils and commutator plates enables continuous torque generation rather than stalling at a single orientation.

Applications and Takeaways

In summary, the DC motor is driven by the interaction between current-induced magnetic fields in the windings and the static magnetic field from the permanent magnets. The rotor carries windings and a commutator, while stationary brushes provide the electrical connection. The design choices, such as using multiple windings at 120-degree intervals and laminating the rotor, are geared toward achieving smoother rotation and higher efficiency. The video closes by inviting viewers to consider where DC motors are used and to share project ideas in the comments, reinforcing the practical engineering value of understanding motor operation.