Troubleshooting Guide

Common problems and solutions for robotics projects. When something isn’t working, start here to diagnose and fix issues quickly.

Hardware Issues
Programming Issues
Electronics Issues
1. LED Strip Not Working
2. Breadboard Circuits
Competition Robot Issues
1. Sumo Robot Problems
  1. Edge Detection Issues
  2. Movement Problems
2. Freeze Tag Robot Problems
  1. Control Responsiveness
Debugging Strategies
1. Systematic Approach
2. Useful Debug Techniques
Getting Help
Prevention Tips
1. Best Practices
2. Common Mistakes to Avoid

Hardware Issues

Robot Won’t Turn On

Symptoms: No lights, no response to buttons

Check battery: Is it charged? Properly connected?
Check power switch: Is it in the ON position?
Check connections: Are all cables firmly seated?
Try different battery: Batteries can fail suddenly

Motors Not Working

Symptoms: Robot doesn’t move despite code running

Check motor connections: Red to positive, black to negative
Verify ports: Motors connected to correct brain ports?
Test motor power: Try a simple test program
Check for binding: Can wheels turn freely by hand?

Sensors Not Responding

Symptoms: Sensor readings are always 0 or max value

Check wiring: 3-wire sensors need power, ground, and signal
Verify port assignment: Code matches physical connection?
Test sensor isolation: Disconnect and test individually
Check for interference: Keep sensor wires away from motors

Programming Issues

Code Won’t Download

Symptoms: Error messages during download process

Check USB connection: Try different cable or port
Brain connection: Is the brain icon green in VEXcode?
Restart software: Close and reopen VEXcode
Update firmware: Brain and controller may need updates

Robot Behaves Erratically

Symptoms: Unpredictable movement or sensor readings

Add delays: wait(20) between loop iterations
Check variable scope: Are variables initialized properly?
Debug with print: Add screen output to see values
Simplify code: Test one feature at a time

Infinite Loops or Freezing

Symptoms: Robot stops responding, code doesn’t advance

Add exit conditions: Every loop needs a way out
Check while conditions: Do they actually change?
Use print statements: Track where code gets stuck
Add timeout limits: Prevent endless waiting

Electronics Issues

LED Strip Not Working

Symptoms: No colors, wrong colors, or flickering

Check power: LEDs need adequate current supply
Verify connections: Data pin to correct micro:bit pin
Test simple pattern: Start with solid colors
Check LED count: Code matches actual LED quantity?

Breadboard Circuits

Symptoms: Components don’t work as expected

Check power rails: Are positive/negative connected?
Verify connections: Components share rows correctly?
Look for loose wires: Push all connections firmly
Check component orientation: LEDs, diodes have polarity

Competition Robot Issues

Sumo Robot Problems

Symptoms: Falls off platform, doesn’t find opponents

Edge Detection Issues

Sensor height: Too high/low to detect white line?
Ambient light: Room lighting affects sensors
Calibration: Run sensor calibration routine
Threshold values: Adjust light/dark detection levels

Movement Problems

Speed too fast: Robot can’t react to sensors quickly
Turning radius: Adjust to stay within ring boundaries
Weight distribution: Heavy front helps with pushing
Wheel traction: Clean wheels, check for wear

Freeze Tag Robot Problems

Symptoms: Poor maneuvering, can’t avoid obstacles

Control Responsiveness

Smoothing factor: Balance stability vs. responsiveness
Speed limits: Too fast = hard to control precisely
Controller deadzone: Small joystick movements ignored
Battery level: Low power affects motor performance

Debugging Strategies

Systematic Approach

Isolate the problem: What specific part isn’t working?
Start simple: Test basic functionality first
Change one thing: Don’t modify multiple things at once
Document changes: Keep track of what you’ve tried
Ask for help: Get fresh eyes on the problem

Useful Debug Techniques

Visual Feedback

# Add to your code to see variable values
brain.screen.clear_screen()
brain.screen.print("Sensor: {}".format(sensor_value))
brain.screen.print("Motor: {}".format(motor_speed))

Step-by-Step Testing

# Test components individually
motor_left.set_velocity(50)
wait(1000)  # Run for 1 second
motor_left.stop()

Boundary Checking

# Ensure values stay within expected ranges
if sensor_value < 0:
    sensor_value = 0
elif sensor_value > 100:
    sensor_value = 100

Getting Help

Self-Help Checklist

Read error messages carefully
Check physical connections
Try a simpler version of your code
Look for similar problems in documentation
Test individual components separately

When to Ask for Help

After trying basics: Don’t give up too quickly, but don’t waste hours either
With specific questions: “My motor won’t turn” vs “nothing works”
With error messages: Copy exact error text
During peer review: Sometimes a teammate spots the issue immediately

How to Ask for Help

Describe the expected behavior: What should happen?
Explain the actual behavior: What actually happens?
List what you’ve tried: Shows your problem-solving effort
Share relevant code: Only the part that’s not working
Mention recent changes: What was the last thing that worked?

Prevention Tips

Best Practices

Save working versions: Before making big changes
Test incrementally: Add one feature at a time
Use clear variable names: left_motor_speed vs x
Comment your code: Explain complex logic
Keep backups: Save multiple versions of working code

Common Mistakes to Avoid

Forgetting to download: Code changes don’t apply until downloaded
Wrong port assignments: Double-check physical vs. code connections
Missing delays: Real-time systems need time between operations
Assuming sensors work: Always test and calibrate sensors first
Ignoring battery level: Low batteries cause mysterious problems

Remember: Every expert was once a beginner who encountered these same problems. Debugging skills improve with practice, and every problem solved makes you a better roboticist!