DC Motors

DC Motors

Goals

  1. Discuss the different types of motors used in small electronic devices

  2. Introduce DC motors

  3. DC motor power considerations

  4. DC motor applications

DC Motor Applications

  • Hobby motors
    • Small electronics
    • Low-torque applications
  • Large DC motors
    • Electric scooters
    • High-torque applications
  • Motors can also generate electricity (generators / alternators)

How Do Brushed Motors Work?

  • Electromagnetism!
  • VERY brief physics aside

Electromagnetism

  • The guiding principle behind electric motors is the Lorentz Force

  • Electrical current in a magnetic field produces a physical force
  • Force direction is given by the “right-hand rule”
    • Current direction along your index
    • Magnetic field along your middle
    • Force direction is along your thumb

Three Main Parts of DC Motor

  • Stator magnets (stationary)
  • Armature / Windings (rotating wire)
  • Commutator (supplies current to armature)

Inside Simple DC Motor

https://cdn.sparkfun.com/assets/a/1/6/0/2/524dcee9757b7f00478b4567.jpg Disected Motor!

DC Motor Construction

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Illustration

dc_motor_illustration

DC Motor Types

Brushed Brushless (synchronous or electronically commutated motor)
Physical contact points in the commutator to switch current direction Inverter to electrically switches the DC power supply to AC power supply
Pro: Relatively inexpensive Pro: Less wear on moving parts
Con: Parts wear out over time Con: More expensive

Exercise

  • Attach fan blade to motor
  • Connect red wire on motor to 3v3; connect black wire to ground
    • What happens?
  • Reverse the wires
    • What happens?
  • Was the speed the same in either case?

Motors

  • Spin is controlled by current direction
  • If direction is reversed, the motor spins in the opposite direction
  • It is not practical to have to reverse the wires to change motor direction
  • Also, we have no way to control speed

Motor Controller

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Motor Driver

  • Motor (motor controller) provide greater control over motors
  • Motor drivers don’t give a (+) or (-) connection
  • Just have an IN1 or IN2 because we can change polarity
  • Motor drivers also provide circuit protection
  • Motor drivers can control two different motors independently

Motor Controller Wiring Guide

Motor Controller Explanation
PWMA Motor A speed (PWM)
AI1, AI2 Motor A direction control (connect to Photon 2)
AO1, AO2 Motor A output (connect to motor)
PWMB, BI1, BI2, BO1, BO2 Controls for motor B
VCC Power for chip (3v3)
VM Power for motors (3v3, or higher for powerful motors)
STBY Enable motor (3v3)
GND Ground

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Controlling the Motor Direction

  • Setting the direction is done by changing the two input pins to HIGH and LOW separatel
    • Ex: AI1 = HIGH and AI2 = LOW is one direction
    • Ex: AI1 = LOW and AI2 = HIGH is other direction
  • Setting them both to LOW means stopping the motor
  • Setting them both to HIGH can damage the motor

Controlling the Motor Speed

  • The PWM method of controlling motor speed operates on this range: [0-255]
  • Typically the PWM must be somewhat greater than 0 before it starts to spin

Wiring Diagram

Screenshot 2024-06-19 at 1.36.01 PM

Wiring Guide

Motor Controller Photon 2
PWMA A5
AI2 D4
AI1 D3
AO1 Motor wire (either)
AO2 Motor wire (either)
VCC 3v3
GND GND
VM 3v3
STBY 3v3

Exercise

  • Attach the fan blade to the DC motor
  • The theoretical PWM values are 0 to 255. Write a sketch to determine the min and max values.
  • Write a sketch that powers up the fan from the practical minimum (the value we established in the previous exercise) to the maximum
  • There should be a ramp up in speed, getting progressively faster until it maxes out

Credits

  • Images created with Fritzing
  • Original slides created by Ray Kim
  • Sparkfun
  • For more in-depth discussion of motors, see this page

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