DC Motor
Motor
A rotary electromechanical device that converts electrical energy into mechanical energy using direct current. The most common type of motor in hobby and industrial applications.
Schematic symbol
Motor
How dc motor appears in a circuit diagram.
Types & variants
Key specs
Voltage
Volt (V)Operating voltage range. Exceeding voltage can damage the motor.
No-load speed
RPMSpeed when running without any load. Higher voltage = higher speed.
No-load current
Ampere (A)Current drawn when running without any load. Indicates efficiency.
Stall current
Ampere (A)Current when motor is stopped but powered. Very high - can damage driver.
Torque
N⋅m or kg⋅cmRotational force the motor can produce. Higher = stronger motor.
Power
Watt (W)Mechanical output power. P = Torque × Angular velocity.
Markings
Usually printed on the motor body: voltage, current, RPM, model number. Gear motors often show gear ratio.
Standard values
Common voltages: 3V, 6V, 12V, 24V. Common sizes: N20, N30, TT, FA-130, 130-size. Power ranges: 0.1W to 100W+.
How to choose
1) Determine required voltage for your project. 2) Calculate needed torque/speed for your application. 3) Consider current requirements (driver must handle stall current). 4) Choose brushed for simplicity, brushless for efficiency/longevity. 5) Add gearbox if high torque at low speed is needed.
Pinout & package
2 terminals for power (polarized + and -). Brushless motors have 3 wires for phases. Packages: cylindrical with shaft, rectangular with gearbox. Larger motors have mounting holes.
Example circuits
- Direct drive with battery and switch
- PWM speed control with transistor/MOSFET
- H-bridge for bidirectional control
- Encoder position feedback system
- Robot wheel drive mechanism
Common failures
Brushes wear out (reduced power, sparking). Bearings wear (noise, wobble shaft). Overheating from excessive current/duty cycle. Gearbox damage (stripped teeth, noise). Open or short windings.
How to test
1) Check continuity between terminals with multimeter (should show low resistance). 2) Apply appropriate voltage briefly - motor should spin. 3) Measure current draw at no-load (should match specs). 4) Check for unusual noise or vibration when running.
Substitutes
Use same voltage and similar torque/speed. Brushless motors can replace brushed with proper controller. Larger motor can replace smaller if power requirements allow. Gearbox can be added to standard motor for more torque.