Motors (work in progress)

  • What are the different types of common motors
  • What are their strengths and weaknesses
  • How to choose them
  • How to control them

Motor Types

  1. Permanent Magnet DC (PMDC) or Brushed DC (BDC) motor:
    1. Identification: 2 wires
    2. Control: Apply power, motor turns. Very simple if only one direction is needed (reverse requires H-bridge of some sort)
    3. Cost: Very inexpensive (starts at $ 0.50)
    4. Speed and torque: High speed, low torque
    5. Position control: None
    6. Feedback (position, speed): None
  2. Hobby Servo Motor
    1. Can provide either
      1. Continuous rotation with reverse, but no position control
      2. Moderately accurate absolute position control limited to 180 degrees
    2. Identification: 3 wires
    3. Control: Essentially no circuit but requires specific waveform to control position or speed. Easy with Arduino, tricky to generate otherwise
    4. Cost: Medium (starts at $10)
    5. Speed and torque: Medium speed, moderate torque
    6. Position control depends on type:
      1. Continuous rotation type: Some speed control, no position control
      2. 180 degree type: Moderately accurate absolute position control
    7. Feedback (position, speed): Some have position feedback (Adafruit)
  3. Stepper Motor
    1. Identification: 4, 6, or 8 wires
    2. Control: Requires H-bridge and sequencing. Easy with Arduino, tricky to generate otherwise. Easily reversed.
    3. Cost: higher (starts at $20), plus requires H-Bridge
    4. Speed and torque: Medium speed, low torque
    5. Feedback (position, speed): None
    6. Extremely accurate relative position control

Changing speed and torque

Adding feedback: where am I?

  • Absolute: limit switches

    • Home
    • End Of Travel
    • Intelligent vs. dumb
  • Relative continuous: encoders


  1. Power supply issues, especially with Hobby Servos
  2. Beware of cautious of published H-bridge capabilities and published motor specifications. Motors can generate extremely short peaks that are much higher than the continuous values which will far exceed and damage the expensive H-Bridge. It is best to be extremely conservative.
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