Troubleshooting Guide¶

Common problems and how to fix them.

"My Robot Won't Move!"¶

Checklist¶

flowchart TD
    Start["Robot Won't Move"] --> B{"Battery charged?"}
    B -->|No| BC["Charge battery"]
    B -->|Yes| C{"Code downloaded?"}
    C -->|No| CD["Download code from brain menu"]
    C -->|Yes| M{"Motors plugged in?"}
    M -->|No| MC["Check connections"]
    M -->|Yes| P{"Ports correct in code?"}
    P -->|No| PC["Match robot_config.py"]
    P -->|Yes| K{"Controller connected?"}
    K -->|No| KC["Check wireless link"]
    K -->|Yes| OK["All checks passed - investigate further"]

Port Mismatch¶

# If motors are on ports 1,2,3,4 but code says 5,6,7,8:
left_motor_front = Motor(Ports.PORT1, ...)  # ← Check this!

Motors Reversed Wrong¶

# If robot spins in circles instead of forward:
# Right motors should be reversed!
right_motor = Motor(Ports.PORT3, GearSetting.RATIO_18_1, True)
#                                                         ^^^^

"My Robot Moves Slowly"¶

Check Gear Setting¶

# Make sure code matches physical cartridge!
Motor(port, GearSetting.RATIO_18_1, ...)  # Green = 200 RPM
Motor(port, GearSetting.RATIO_36_1, ...)  # Red = 100 RPM

Check Velocity Setting¶

# Make sure velocity is high enough
motor.set_velocity(100, PERCENT)  # Not 10!

Battery Low¶

Check battery percentage on brain screen
Swap batteries if below 50%

"My Robot Drifts When Joystick Is Centered"¶

Add Deadband¶

def deadband(value, threshold=5):
    if abs(value) < threshold:
        return 0
    return value

speed = deadband(controller.axis3.position())

Increase Threshold¶

# If still drifting, increase threshold
speed = deadband(controller.axis3.position(), threshold=10)

"My Robot Overshoots When Turning"¶

Reduce Turn Velocity¶

drivetrain.set_turn_velocity(30, PERCENT)  # Lower = more accurate

Add Wait After Turn¶

drivetrain.turn_for(RIGHT, 90, DEGREES)
wait(200, MSEC)  # Let robot settle

Use Inertial Sensor¶

# For accurate turns, use inertial sensor + P control
# See Tutorial 7.1: PID Control

"Code Doesn't Download"¶

Check Connection¶

USB-C cable connected to Brain?
VEX Extension active in VS Code?
Brain powered on?

Try Restart¶

Power off brain
Disconnect USB
Power on brain
Reconnect USB
Try download again

Check File¶

Make sure you're downloading main.py
Check for syntax errors (red underlines)

"Controller Doesn't Work"¶

Check Pairing¶

Both brain and controller powered on?
Radio dongle plugged into brain?
Try re-pairing (hold power buttons on both)

Wired Test¶

Connect controller to brain with cable
If works wired but not wireless, battery issue

Replace Batteries¶

Controller takes AA batteries
Replace if older than a few months

Common Code Errors¶

IndentationError¶

# WRONG:
def my_function():
print("Hello")  # Not indented!

# RIGHT:
def my_function():
    print("Hello")  # 4 spaces

NameError¶

# WRONG:
print(Speed)  # Wrong capitalization

# RIGHT:
print(speed)  # Match variable name exactly

TypeError¶

# WRONG:
print("Speed: " + speed)  # Can't add string + number

# RIGHT:
print("Speed: " + str(speed))  # Convert to string

SyntaxError¶

# WRONG:
if speed > 50  # Missing colon
    print("Fast")

# RIGHT:
if speed > 50:  # Colon required!
    print("Fast")

Inertial Sensor Issues¶

Not Calibrated¶

inertial_sensor.calibrate()
wait(3, SECONDS)  # MUST WAIT for calibration!

Robot Moving During Calibration¶

Robot must be STILL during calibration
Place on flat surface
Don't touch for 3 seconds

Heading Drift¶

Normal over time
Re-calibrate between matches
Use inertial_sensor.set_heading(0) to reset

Distance Sensor Issues¶

Reading Zero¶

Object too far? (Max ~2000mm)
Object too close? (Min ~50mm)
Sensor blocked?

Inconsistent Readings¶

Shiny surfaces reflect poorly
Dark objects absorb light
Try different target surface

Competition Checklist¶

timeline
    title Competition Pre-Match Checklist
    section BEFORE MATCH
        Battery charged >70%
        : Controller batteries fresh
        : Code downloaded
        : Correct autonomous selected
        : Motors all working
        : Sensors calibrated
    section AT FIELD
        Controller paired
        : Alliance color set (if needed)
        : Starting position correct
        : Robot in legal position
    section AFTER AUTONOMOUS
        Ready to drive immediately
        : Know the game situation

Getting More Help¶

VEX Forum: www.vexforum.com
VEX Knowledge Base: kb.vex.com
Ask Your Mentor
Check the Glossary (next page)

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