// Section 01

Autonomous Failure Types

Every auton failure has a root cause. Identify the type first — then trace backward.

⚠️

Before touching code: Verify the robot is physically identical to when auton last worked. Loose screws, changed compression, or shifted sensors cause most failures.

The Four Failure Types

🚫 Does Nothing

Robot sits still. Wrong brain slot, compile error, or driver control is running. Check the brain slot selection screen.

🔄 Drifts Off Path

Robot moves but curves. IMU drift, wheel mismatch, or motor speed offset. Usually mechanical or calibration-related.

⏳ Stops Early

Completes some moves then freezes. Exit condition never triggers or motor stalls. Check timeouts and sensor readings.

🎯 Inconsistent

Works sometimes, fails others. Battery level, field variation, or starting position. Systematic — not random.

First-Check Checklist

Confirm the correct brain slot is selected

On competition day the most common "auton failure" is running the wrong slot. Select your auton routine explicitly before every match — do not assume it remembered from last time.

Check battery charge

Anything below 60% will cause undershooting on drive moves. Use a new or fully charged battery for every match. Log the battery percentage when issues occur.

Verify starting position

Place the robot in exactly the same position every run. A half-inch error at the start compounds through every subsequent move.

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// Section 02

Drift & Positioning Failures

Robot ends up in the wrong place. The most fixable category of auton failure.

Symptom	Likely Cause	Fix
Curves consistently left/right	Wheel diameter mismatch or motor offset	Check wheel sizes; add drive correction constant
Right direction, wrong distance	Track width incorrect in chassis config	Measure precisely: outside wheel edge to outside wheel edge
Fine at first, drifts later	IMU heading accumulation error	Add `chassis.turnToHeading(0)` between moves
Random drift each run	Battery variation or floor surface	Full battery; run on match-quality foam tiles
Spins instead of moving forward	Left/right motors swapped in port config	Verify port numbers and directions in EZ setup

IMU Heading Check

Let IMU fully calibrate — never move during this

Calibration takes 2–3 seconds at startup. Any vibration or movement during this window corrupts the heading reference for the entire match.

Print heading before first move

Add Brain.Screen.print(imu.heading()); before your first drive command. It should read 0.0 (or your defined start heading). Non-zero means calibration failed.

Verify less than 1 degree drift over 10 seconds

Let the robot sit still after calibration and watch the heading value. More than 1 degree of drift indicates a poorly mounted IMU or a defective sensor.

💡

Build a starting jig: Cut a C-channel piece to rest against the tile edge. Place the robot against it each run. Removes starting position variation in 2 seconds flat.

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// Section 03

Hangs & Timeouts

Auton starts correctly then stops mid-routine. An exit condition never fires, or a motor stalls.

Every movement in EZ Template waits for an exit condition — a threshold that signals arrival. If the robot is physically blocked or the motor stalls, it waits until a timeout fires. If no timeout is set, it waits forever.

⏳ No Timeout Set

chassis.set_drive_exit_conditions(1.5, 300, 0) — timeout of 0 means infinite wait. Always set a positive timeout in milliseconds.

🚫 Motor Stall

Motor reaches stall current pushing against an obstacle. Add stall detection or reduce the move distance. Check for mechanical binding.

🎯 Threshold Too Tight

Robot oscillates near target but never settles within 0.1 inches. Loosen: 0.5–1 inch for drive, 1–2 degrees for turns.

Setting Exit Conditions in EZ Template

Drive exit conditions

chassis.set_drive_exit_conditions(settle_error, settle_time_ms, timeout_ms);
Recommended start: chassis.set_drive_exit_conditions(1.5, 300, 2000);

Turn exit conditions

chassis.set_turn_exit_conditions(settle_error_deg, settle_time_ms, timeout_ms);
Recommended start: chassis.set_turn_exit_conditions(1, 300, 1500);

Detect when timeout fires

After a move completes, check chassis.drive_exit_output(). If it returns EXIT_OUTPUT::TIMEOUT, the robot did not reach its target — the next move may be in the wrong position.

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// Section 04

Consistency & Competition

Auton works in practice, fails at competition. The environment changed. Your auton needs to be robust to variation.

🔋 Battery Level

Low battery slows motors and shortens drive distances 5–10%. Run auton on below-70% battery in practice to verify it still works.

🗻 Tile Variation

Competition tiles may be worn or warped. PID-tuned closed-loop movements handle this. Open-loop timed movements do not.

🏛 Starting Position

Half an inch off compounds through every move. Use a physical jig or tile edge reference every single run without exception.

🏃 Opponent Interference

A robot or game piece blocking your path deflects auton. Design routes that avoid the center. Use timeouts to recover and continue.

Pre-Competition Auton Checklist

Test at 80% battery the night before

Discharge a battery to 80%, then run your full auton sequence. If it passes at 80%, it will pass at competition. If it fails, your PID needs tightening.

Run on a practice field at the venue before matches

If possible, request a practice field run before eliminations. One run on competition-specific tiles is worth more than 20 runs in your garage.

Log battery, slot, and result for every match

Have a teammate record: battery percentage, which slot ran, and what happened. After 3 matches of logging, patterns emerge and problems become obvious.

💡

The real fix for inconsistency is PID, not tweaking constants: If you are adjusting distances by hand for each competition, your drive train is not properly closed-loop. Invest in proper EZ Template PID tuning once — it pays off for the rest of the season.

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