Tutorial 5.1: Basic Autonomous Movements

Time: ~15 minutes Prerequisites: Tutorial 4: Drive Control

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What is Autonomous?

During the first 15 seconds of a VEX match, no human control is allowed. Your robot must execute pre-programmed movements on its own!

flowchart LR
    subgraph Autonomous ["Autonomous (0-15s)"]
        A1[Programmed code runs]
        A2[No human control]
    end
    subgraph Driver ["Driver Control (15s-2min)"]
        D1[Human driver takes over]
        D2[Full controller access]
    end
    Autonomous --> Driver

The DriveTrain Commands

drive_for() - Move Forward/Backward

# Drive forward 500mm
drivetrain.drive_for(FORWARD, 500, MM)

# Drive backward 300mm
drivetrain.drive_for(REVERSE, 300, MM)

# Drive forward 12 inches
drivetrain.drive_for(FORWARD, 12, INCHES)

Parameters:

Parameter	Options	What It Does
Direction	FORWARD, REVERSE	Which way to move
Distance	Number	How far to travel
Units	MM, INCHES	What unit for distance

turn_for() - Rotate in Place

# Turn right 90 degrees
drivetrain.turn_for(RIGHT, 90, DEGREES)

# Turn left 45 degrees
drivetrain.turn_for(LEFT, 45, DEGREES)

# Full 180° turn
drivetrain.turn_for(RIGHT, 180, DEGREES)

    TURNING VISUALIZED:

    Before:                After turn_for(RIGHT, 90):

       ↑                          →
    +-----+                    +-----+
    |     |                    |     |
    +-----+                    +-----+

Code Walkthrough: autonomous.py

def setup_autonomous():
    """Configure drivetrain settings for autonomous mode."""
    drivetrain.set_drive_velocity(50, PERCENT)  # Movement speed
    drivetrain.set_turn_velocity(30, PERCENT)   # Turn speed
    drivetrain.set_stopping(BRAKE)               # How to stop
    drivetrain.set_timeout(3, SECONDS)           # Max time per move

def autonomous_routine():
    """Main 15-second autonomous routine."""
    brain.screen.print("Autonomous Started")

    setup_autonomous()

    # Example moves (replace with your strategy):
    drivetrain.drive_for(FORWARD, 500, MM)
    wait(200, MSEC)

    drivetrain.turn_for(RIGHT, 90, DEGREES)
    wait(200, MSEC)

    drivetrain.drive_for(FORWARD, 300, MM)
    wait(200, MSEC)

    brain.screen.print("Autonomous Complete")

Understanding set_timeout()

What if your robot gets stuck? set_timeout() prevents infinite waiting:

drivetrain.set_timeout(3, SECONDS)  # Max 3 seconds per move

# If drive_for takes longer than 3 seconds,
# the robot gives up and moves to the next command
drivetrain.drive_for(FORWARD, 1000, MM)  # Will stop after 3 sec if stuck

flowchart TD
    subgraph without["Without Timeout"]
        A1["drive_for(1000mm)"] --> B1["Robot stuck!"]
        B1 --> C1["Waits forever..."]
        C1 --> D1["NEVER CONTINUES"]
    end

    subgraph with["With Timeout (3 seconds)"]
        A2["drive_for(1000mm)"] --> B2["Robot stuck!"]
        B2 --> C2{"3 seconds pass"}
        C2 --> D2["Continues to next command!"]
    end

Stopping Modes

drivetrain.set_stopping(COAST)  # Free-spin to stop
drivetrain.set_stopping(BRAKE)  # Active braking (recommended)
drivetrain.set_stopping(HOLD)   # Hold position firmly

    COAST                BRAKE                HOLD

    ⟳ → ⟳ → ⟳ → stop     ⟳ → ⟳ → X           ⟳ → X (locked!)
    Slowly coasts        Quick stop           Resists movement
    Good for: speed      Good for: accuracy   Good for: holding

Driving a Square Pattern

Here's how to drive a square:

def drive_square():
    setup_autonomous()

    for i in range(4):  # Repeat 4 times
        drivetrain.drive_for(FORWARD, 500, MM)
        wait(200, MSEC)
        drivetrain.turn_for(RIGHT, 90, DEGREES)
        wait(200, MSEC)

    Square Pattern:

    START/END
        ●━━━━━━━━━●
        │         │
        │         │   Each side: 500mm
        │         │   Each turn: 90°
        ●━━━━━━━━━●

Why wait() Between Moves?

Without wait(), the robot might not fully stop before starting the next move:

# WITHOUT wait - robot might drift
drivetrain.drive_for(FORWARD, 500, MM)
drivetrain.turn_for(RIGHT, 90, DEGREES)  # Might start before fully stopped!

# WITH wait - robot stabilizes
drivetrain.drive_for(FORWARD, 500, MM)
wait(200, MSEC)  # 0.2 seconds to settle
drivetrain.turn_for(RIGHT, 90, DEGREES)

Velocity Settings

# Slow but accurate
drivetrain.set_drive_velocity(30, PERCENT)
drivetrain.set_turn_velocity(20, PERCENT)

# Fast but might overshoot
drivetrain.set_drive_velocity(80, PERCENT)
drivetrain.set_turn_velocity(50, PERCENT)

# Balanced (recommended starting point)
drivetrain.set_drive_velocity(50, PERCENT)
drivetrain.set_turn_velocity(30, PERCENT)

Trade-off: | Speed | Accuracy | Battery | Best For | |-------|----------|---------|----------| | Low | High | Lower use | Precise movements | | High | Lower | Higher use | Distance coverage |

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Exercise: Drive a Triangle

Goal: Program the robot to drive a triangle pattern.

Hint: A triangle has: - 3 sides (each needs drive_for) - 3 corners (each needs turn_for) - Each turn is 120° (360° ÷ 3 = 120°)

def drive_triangle():
    setup_autonomous()

    for i in range(3):
        drivetrain.drive_for(FORWARD, _____, MM)
        wait(200, MSEC)
        drivetrain.turn_for(RIGHT, _____, DEGREES)
        wait(200, MSEC)

Fill in the blanks!

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Answer

def drive_triangle():
    setup_autonomous()

    for i in range(3):
        drivetrain.drive_for(FORWARD, 400, MM)  # Any distance works
        wait(200, MSEC)
        drivetrain.turn_for(RIGHT, 120, DEGREES)  # 360/3 = 120
        wait(200, MSEC)

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