Motors and Arduino for Robotics

Week 2 • CMPSC 304 Robotic Agents

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Today's Agenda

  • Arduino Uno basics and power flow
  • Digital vs. Analog signals
  • Pulse Width Modulation (PWM)
  • Battery voltage calculations
  • Why we need motor drivers
  • DC motors for Project 1
  • Motor types overview

Arduino Uno Overview

USB Connection

Arduino USB Port
  • Used to upload code to the Arduino microcontroller
  • Powers the Arduino during programming
  • Enables serial communication for debugging

Digital Input/Output Pins (0-13)

Arduino Digital Pins
  • Pins can be HIGH (5V) or LOW (0V)
  • Outputs: Turn on an LED every 10 seconds to make it blink
  • Inputs: Read sensor data (e.g., is surface wet or dry?)
  • Pins with ~ symbol: Support PWM (Pulse Width Modulation)
  • PWM pins: 3, 5, 6, 9, 10, 11

Analog Input Pins (A0-A5)

Arduino Analog Pins
  • Can read a range of values (0-1023)
  • Perfect for sensors with continuous output
  • Examples: Distance sensors, light sensors, temperature sensors, potentiometers

Power and Ground Connections

Arduino Power Pins
  • 5V pin: Provides 5 volts (HIGH)
  • 3.3V pin: Provides 3.3 volts (for sensitive components)
  • GND pins: Ground/reference voltage (LOW, 0V)
  • Vin: Input voltage (7-12V recommended)
  • Circuits flow from GND to HIGH to complete the circuit

Digital vs. Analog Signals

Digital

HIGH (5V) or LOW (0V)
  • ON or OFF (like light switch)
  • Pins 0-13
  • digitalWrite(13, HIGH)

Analog

Range: 0V to 5V
  • Continuous values (like dimmer)
  • Reads 0-1023 (Pins A0-A5)
  • analogRead(A0)

Pulse Width Modulation (PWM)

Problem: Arduino digital pins are only HIGH or LOW

Question: How do we get "in-between" voltages?

Answer: PWM = rapidly switching between HIGH and LOW!

How PWM Works

Rapidly switch HIGH/LOW → Motor sees average voltage

Duty Cycle Examples:

  • 25% duty cycle: 0.25 × 5V = 1.25V
  • 50% duty cycle: 0.50 × 5V = 2.5V
  • 75% duty cycle: 0.75 × 5V = 3.75V
  • 100% duty cycle: 1.00 × 5V = 5V

PWM on Arduino

PWM pins (marked with ~): 3, 5, 6, 9, 10, 11

analogWrite(9, 0);    // 0% duty cycle = 0V (motor stopped)
analogWrite(9, 64);   // 25% duty cycle = 1.25V (slow)
analogWrite(9, 128);  // 50% duty cycle = 2.5V (medium)
analogWrite(9, 191);  // 75% duty cycle = 3.75V (fast)
analogWrite(9, 255);  // 100% duty cycle = 5V (full speed)
PWM values: 0-255 (not 0-1023 like analogRead!)

Why PWM for Motors?

  • ✓ Efficient: Minimal heat
  • ✓ Simple: No voltage regulation
  • ✓ Precise: 256 speed levels (0-255)
  • ✓ Digital pins: No analog output needed
Motor inertia smooths pulses → steady voltage

Battery Voltage: 4 AA Batteries

Question: Yellow DC motor kit comes with 4 AA battery holder. What voltage is this?

Answer: 6 volts

How Do We Know?

AA battery = 1.5V (1.2V rechargeable)

Series connection: Voltages ADD

4 × 1.5V = 6V total

Series vs. Parallel Batteries

Series: Voltages ADD

  • End-to-end: 1.5V + 1.5V + 1.5V + 1.5V = 6V
  • Capacity: Same (2000 mAh)

Parallel: Capacity ADDS

  • Side-by-side: Voltage stays 1.5V
  • Capacity: 4 × 2000 = 8000 mAh

Battery Voltage Over Time

Battery State Alkaline AA Your 4× AA Pack
Fresh 1.5V - 1.6V 6.0V - 6.4V
Nominal 1.5V 6.0V
50% used 1.3V 5.2V
Depleted 1.0V 4.0V
⚠️ Motors slow down as batteries drain!

Why We Need Motor Drivers

Critical Problem: Arduino pins cannot directly power motors!

Arduino Pin Limitations

Arduino Pin

  • Max: 20-40 mA

DC Motor

  • Needs: 150-300 mA
  • Stall: 1-2 A
Motor draws 10× more than Arduino!

What Happens Without a Driver?

✗ Direct connection

  • Pin tries to supply 150+ mA
  • Rated for only 20-40 mA
  • → Damaged Arduino!

✗ Motor stalls

  • Current spikes to 1-2 A
  • → Permanent damage!

Motor Driver to the Rescue!

Power bridge controlled by low-current signals

  1. Arduino: LOW current control (< 20 mA)
  2. Driver: HIGH current from battery (1-2 A)
  3. Motor powered by battery, not Arduino
  4. Arduino stays safe!

Motor Driver Functions

  • ✓ Current amplification
  • ✓ Direction control (H-bridge)
  • ✓ Speed control (PWM)
  • ✓ Protection (overcurrent)
  • ✓ Isolation (reduces noise)

Breadboard Basics

Breadboard
  • Solderless prototyping
  • Horizontal rows: Connected
  • Vertical rails: Power/GND
  • Red: + voltage (5V)
  • Blue/Black: Ground (GND)

DC Motors for Project 1

Yellow Geared DC Motors

  • Type: Brushed DC with gears
  • Voltage range: 3-6V (motor's operating range)
  • Your power: 4× AA = 6V (at upper limit)
  • Application: Wheeled robot
  • Features:
    • Gears reduce speed, increase torque
    • Two-wire control (polarity = direction)
    • Current: 150-300 mA (1-2A stall)

Motor Driver: L298N

  • Controls: Speed & direction
  • H-Bridge: Bidirectional control
  • Specs:
    • 2 motors, up to 2A each
    • Logic: 5V, Motor: 5-35V
  • Pins:
    • IN1/IN2: Motor A direction
    • IN3/IN4: Motor B direction
    • ENA/ENB: Speed (PWM)

Alternative Motor Drivers

TB6612FNG

  • More efficient
  • Up to 1.2A/channel

WWZMDiB

  • Compact design
  • Space-saving
Any driver works for Project 1!

Next Steps for Project 1

  1. Mechanical build, wiring, power
  2. Install fresh batteries (6V)
  3. Test motors before mounting
  4. Verify driver connections
  5. Start with low PWM (50-100)
  6. Document your wiring

Types of Electric Motors

  • Brushed DC Motors (what you're using)
  • Brushless DC Motors
  • Stepper Motors
  • Servo Motors

Brushed DC Motors

Pros

  • Simple control
  • Inexpensive
  • Widely available

Cons

  • Brush wear
  • Lower efficiency
  • Needs maintenance

Brushless DC Motors

Pros

  • Higher efficiency
  • Longer lifespan
  • More torque/weight

Cons

  • Needs ESC
  • More expensive
  • Complex control

Use: Drones, RC cars

Stepper Motors

Pros

  • Precise positioning
  • Holds position
  • No encoder needed

Cons

  • Lower speed
  • Can lose steps
  • Needs driver

Use: 3D printers, CNC

Servo Motors

Types

  • Standard: 0-180°
  • Continuous: 360° speed control
  • Digital: Faster, stronger
Built-in control, easy to use, compact

Use: RC vehicles, arms

Other Actuation Technologies

Hydraulic

  • Pressurized liquid
  • Very high force
  • Large, expensive
  • Use: Construction

Pneumatic

  • Compressed air
  • Lightweight, safe
  • Lower force
  • Use: Soft robotics

Safety Considerations

Active

  • Torque limiting
  • Collision detection
  • Emergency stop

Passive

  • Mechanical limits
  • Compliant materials
  • Fail-safe brakes
  • Fuses/breakers

Key Takeaways

  • Digital = ON/OFF; Analog = range; PWM = fast switching
  • 4× AA = 6V (series)
  • Arduino pins cannot power motors directly
  • Motor drivers amplify & protect
  • PWM controls speed (0-255)
  • Motor types: trade-offs in precision, force, speed, cost

Questions?