DC Motor
A brushed DC motor converts DC electrical energy into rotary mechanical energy. Current through the armature winding produces a torque against the stator's permanent-magnet field; a mechanical commutator and carbon brushes flip the armature current twice per turn so torque always drives the same direction.
The rotor (armature) carries multiple winding loops connected to a split copper commutator. Stationary spring-loaded carbon brushes ride on the commutator, feeding current to whichever winding is currently aligned to produce maximum torque. As the rotor turns, the commutator switches the current to the next winding, maintaining torque. The stator is a permanent magnet (small motors) or wound field (large motors).
In plain terms
An electromagnet that flips its own polarity twice per turn so it keeps chasing the permanent magnets around it.
Why designers use it
- A selected brushed DC motor can provide rotation with a relatively simple power stage.
- Speed, direction and braking can be controlled with a suitable driver and control strategy.
Best for
- Toys & tools
- Cordless drills
- Auto window motors
Key specifications
- Voltage: 1.5 – 48 V common
- No-load speed: 3,000 – 30,000 RPM
- Stall current: 5 – 50× no-load
- Efficiency: 40 – 80 %
- Brush life: 100 – 5,000 hours
When not to use it
- When brush wear, acoustic noise, electrical noise or maintenance requirements make the selected motor unsuitable.
- When accurate position control is needed but the system has no suitable feedback and controller.
Common mistakes
- Connecting a motor directly to a GPIO without checking current and voltage limits. Use an appropriate power driver.
- Ignoring the driver's recirculation paths, transient protection and layout requirements.
- Sizing the supply and driver only for normal running current rather than checking starting, stall and thermal conditions.
Where you will find it
- An illustrative low-voltage brushed-motor system uses a controller for commands and a power stage for winding current.
- A blocked rotor is a fault condition to assess, not an inherently safe operating mode. Current limiting, timeout and thermal protection must be designed for the motor and load.
A short history
The first practical commutated DC motor was demonstrated by William Sturgeon in 1832 and turned into a commercial product by Thomas Davenport (US patent 132 in 1837 — the very first US patent for an electric motor). DC motors dominated industrial electrification through the late 19th century until Tesla's AC induction motor displaced them for fixed-speed loads. Permanent-magnet brushed DC motors (cheap ferrite, then neodymium) became ubiquitous in 20th-century consumer goods.
Good to know
- Brushed DC motors emit a characteristic 'EMF crackle' on the supply rail — every commutation arc generates broadband RFI.
- A motor's 'KV rating' (RPM per volt) is just 1/Ke (back-EMF constant) flipped — they describe the same physics.
- The carbon brush wears out first; replacing brushes restores the motor in industrial DC drives that have been running 30+ years.