Tutorial 2.3: Sensors Overview

Time: ~10 minutes Prerequisites: Tutorial 2.2: Motors and Gears

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What Are Sensors?

Sensors let your robot "see" and "feel" the world around it. Without sensors, your robot is blind - it just follows instructions without knowing what's actually happening.

    Without Sensors:              With Sensors:

    "Drive forward 1000mm"        "Drive until you see a wall"

    +--------+                    +--------+
    |  BLIND |  →→→→→ CRASH!      | SENSOR |  →→→→ STOP!
    +--[O][O]+                    +--[O][O]+
                                       ↑
                                  "I see something!"

Available VEX V5 Sensors

Inertial Sensor (IMU)

Like a compass + tilt sensor combined

    ┌─────────────┐
    │   INERTIAL  │
    │   SENSOR    │
    │             │
    │  Measures:  │
    │  - Heading  │  ← Which way you're pointing
    │  - Rotation │  ← How much you've turned
    │  - Tilt     │  ← Are you level?
    │  - Accel    │  ← Are you moving?
    └─────────────┘

Best for: Accurate turning in autonomous, detecting collisions

Distance Sensor

Like robot sonar - measures how far away things are

    +--------+
    |        |  →→→→→→→→→→→→→ WALL
    | DIST   |       ↑
    | SENSOR |   "Distance: 500mm"
    +--------+

Best for: Wall following, stopping before obstacles

Optical Sensor

Detects colors and light levels

    +--------+
    |OPTICAL | ↓ (points down at field)
    +--------+
        ↓
    ▓▓▓▓▓▓▓▓  ← Object color detected!

Best for: Detecting block colors, line following

GPS Sensor

Knows exactly where you are on the field

    FIELD MAP:

    +-----------------+
    |        N        |
    |                 |
    | W      📍     E |  ← "Position: (300mm, 450mm)"
    |                 |
    |        S        |
    +-----------------+

Best for: Precise autonomous navigation, returning to positions

Code Connection: Sensor Setup

Look at src/robot_config.py (lines 67-74):

# =============================================================================
# SENSORS (add as needed)
# =============================================================================
# Uncomment and configure sensors when you add them:
#
# inertial_sensor = Inertial(Ports.PORT5)
# distance_sensor = Distance(Ports.PORT6)
# optical_sensor = Optical(Ports.PORT7)
# gps_sensor = Gps(Ports.PORT8)

These are commented out because the basic robot doesn't have sensors installed yet. When you add a sensor, uncomment the line and update the port number.

Using the Inertial Sensor

The inertial sensor is the most useful for competition robots:

# Setup
inertial_sensor = Inertial(Ports.PORT5)

# IMPORTANT: Calibrate before use!
inertial_sensor.calibrate()
wait(3, SECONDS)  # Wait for calibration

# Read heading (0-360 degrees)
heading = inertial_sensor.heading()  # Returns 0-359.99

# Read rotation (continuous, can be negative)
rotation = inertial_sensor.rotation()  # Can be -999999 to +999999

flowchart LR
    subgraph HEADING["Heading (0-360)"]
        direction TB
        H1["Start: 0"]
        H2["Turn right 45: 45"]
        H3["Turn right 45: 90"]
        H4["Turn right 290: 20"]
        H5["Turn left 30: 350"]
        H1 --> H2 --> H3 --> H4 --> H5
    end
    subgraph ROTATION["Rotation (continuous)"]
        direction TB
        R1["Start: 0"]
        R2["Turn right 45: 45"]
        R3["Turn right 45: 90"]
        R4["Turn right 290: 380<br/>Keeps counting!"]
        R5["Turn left 30: 350"]
        R1 --> R2 --> R3 --> R4 --> R5
    end

SmartDrive: DriveTrain + Inertial

When you add an inertial sensor, you can upgrade to SmartDrive:

# From robot_config.py (commented):
# smart_drivetrain = SmartDrive(
#     left_motors,
#     right_motors,
#     inertial_sensor,       # ← The magic ingredient!
#     WHEEL_TRAVEL_MM,
#     TRACK_WIDTH_MM,
#     WHEEL_BASE_MM,
#     MM,
#     EXTERNAL_GEAR_RATIO
# )

SmartDrive automatically uses the inertial sensor for more accurate turns!

Using the Distance Sensor

# Setup
distance_sensor = Distance(Ports.PORT6)

# Read distance
dist = distance_sensor.object_distance(MM)  # Distance in mm

# Example: Stop before hitting a wall
while True:
    if distance_sensor.object_distance(MM) < 100:
        drivetrain.stop()
    else:
        drivetrain.drive(FORWARD)

    Distance Sensor Range:

    CLOSE            MEDIUM           FAR
    < 100mm          100-500mm        500-2000mm

    +--------+        +--------+      +--------+
    | DIST   |→       | DIST   |→→→   | DIST   |→→→→→→→
    +--------+        +--------+      +--------+

Using the Optical Sensor

# Setup
optical_sensor = Optical(Ports.PORT7)

# Turn on the light for color detection
optical_sensor.set_light_power(100)
optical_sensor.set_light(LedStateType.ON)

# Detect if object is present
if optical_sensor.is_near_object():
    # Read the color
    color = optical_sensor.color()

    if color == Color.RED:
        print("Red block detected!")
    elif color == Color.BLUE:
        print("Blue block detected!")

Sensor Comparison Table

Sensor	Measures	Best For	Ports Used
Inertial	Rotation, tilt, acceleration	Accurate turns	1
Distance	Distance to objects (mm)	Wall detection	1
Optical	Color, light level	Block detection	1
GPS	X, Y position on field	Field navigation	1
Limit Switch	Contact (pressed/not)	Arm limits	1 3-wire
Bumper	Contact (pressed/not)	Wall touch	1 3-wire

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Why Sensors Matter for Push Back

In Push Back, sensors can give you an edge:

    Without Inertial:               With Inertial:

    "Turn right 90°"                "Turn until heading = 90°"

    Might turn 85° or 95°           Always turns exactly 90°
    (motor slip, friction)          (sensor confirms angle)

Sensor Ideas for Push Back

Sensor	Competition Use
Inertial	Accurate autonomous turns, detect being pushed
Distance	Detect goals, detect blocks nearby
Optical	Know if block is your color or opponent's
GPS	Return to specific field positions

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Summary

Sensor	Setup Code	Main Method
Inertial	Inertial(Ports.PORT#)	.heading(), .rotation()
Distance	Distance(Ports.PORT#)	.object_distance(MM)
Optical	Optical(Ports.PORT#)	.color(), .is_near_object()
GPS	Gps(Ports.PORT#)	.x_position(), .y_position()

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Exercise: Add an Inertial Sensor

Goal: Modify robot_config.py to add an inertial sensor on Port 5.

Step 1: Find this line in robot_config.py:

# inertial_sensor = Inertial(Ports.PORT5)

Step 2: Uncomment it by removing the #:

inertial_sensor = Inertial(Ports.PORT5)

Step 3: Write code to display the heading on the brain screen:

# In main.py or a test file:
inertial_sensor.calibrate()
wait(3, SECONDS)

while True:
    brain.screen.clear_screen()
    brain.screen.set_cursor(1, 1)
    heading = inertial_sensor.heading()
    brain.screen.print("Heading: " + str(heading))
    wait(100, MSEC)

Question: What happens to the heading value when you rotate the robot?

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Answer

When you rotate the robot: - Clockwise (right): Heading increases (0 → 90 → 180 → 270 → 0) - Counter-clockwise (left): Heading decreases (0 → 270 → 180 → 90 → 0) - Heading always stays between 0 and 360 degrees

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