🧯 Common Errors

This page catalogs the most frequent failures in the LIMO system, how to recognize them (by logs or symptoms), step-by-step fixes, and how to prevent them next time.

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🪵 Most Common Errors — By Log Message

❌ Nav2 server not ready!

Where it appears: mission_manager.py

Why it happens: Nav2 is still starting when Mission Manager tries to send a goal.

Fix (step-by-step):

1. Stop everything (Ctrl+C).
2. Start Nav2 alone and wait for "Lifecycle nodes are active."

   ros2 launch limo_bringup limo_nav2.launch.py map:=/path/to/map.yaml

3. If stable, re-run full launch. If using full_system.launch.py, increase the TimerAction delay for Mission Manager by +3–5s.

Prevention:

• Keep Mission Manager start ≥ 10s after Nav2 (TimerAction).
• Avoid CPU spikes (close browsers/RViz while starting).

❌ Goal rejected.

Where: mission_manager.py during navigate_to_pose

Causes: invalid frame, unreachable goal, AMCL not localized, or costmap thinks the goal is in an obstacle.

Fix:

1. Confirm frames:

   ros2 run tf2_tools view_frames.py && evince frames.pdf

2. Check goal is in map:
   • RViz → "2D Pose Estimate" → confirm robot is roughly correct.
3. Try a nearby reachable goal (clear of obstacles).
4. Clear costmaps:

   ros2 service call /global_costmap/clear_entirely_std_srvs/Empty {}
   ros2 service call /local_costmap/clear_entirely_std_srvs/Empty {}

Prevention:

• Use valid map + correct origin/resolution in .yaml.
• Run pose_setter.py only after Nav2 + map server are up.

YOLO: no frames / depth invalid

Where: object_detector.py

Symptoms/logs: No /yolo/annotated, warnings like [SKIP] No valid depth at (cx,cy).

Fix:

1. Verify topics exist:

   ros2 topic list | grep -E "camera|image|depth"

2. Ensure depth encoding is 16UC1; reconfigure camera if needed.
3. Confirm intrinsics publishing:

   ros2 topic echo /camera/color/camera_info -n1

4. If depth alignment is off, re-seat camera or adjust static TF (camera→base_link).

Prevention:

• Keep camera TF fixed and correct (static_transform_publisher).
• Clean lens; avoid reflective floors (depth dropouts).

[❌ TF FAIL] Even 'now' failed

Where: object_detector.py (map transform)

Why: TF tree incomplete or wrong frame names; timestamp mismatch.

Fix:

1. Inspect TF:

   ros2 run tf2_tools view_frames.py && evince frames.pdf

2. Ensure depth_msg.header.frame_id equals your camera link (e.g., camera_link).
3. Start the static_transform_publisher before YOLO node.
4. Retry with reduced transform timeout (already handled in code) after frames are steady.

Prevention:

• Launch the static TF node early (TimerAction before detector).

MyCobot: connection / no motion

Where: pick_node.py / drop_node.py

Symptoms: No movement, or socket error.

Fix:

1. Ensure hotspot MyCobotWiFi2.4G / pass mycobt123 is ON.
2. Ping detected IP (from auto-scan) or fallback:

   ping 192.168.137.75

3. Run arm node directly with IP:

   ros2 run mycobot_arm pick_node --ros-args -p m5_ip:=192.168.137.75

4. Power-cycle the arm; re-run.

Prevention:

• Keep the arm on stable power; avoid sharing the 2.4GHz band with heavy traffic.

No initial pose set

Where: Nav2/AMCL feels "lost"

Logs: Goals fail or robot spins in place.

Fix:

1. Confirm pose_setter log:

   ✅ Initial pose published at (...)

2. In RViz, manually use "2D Pose Estimate" once, then retry goals.

Prevention:

• Delay pose_setter.py ~2–3s after Nav2 + map server (already in launch).

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🧭 Most Common Errors — By Symptom

Robot doesn't move

Likely causes: Nav2 not ready, invalid goal, emergency stop.

Checklist:

1. /navigate_to_pose exists?

   ros2 action list | grep navigate

2. Costmaps valid?
3. Battery > 50%?
4. Try a short 0.5m forward goal in free space.

Robot drifts / wrong localization

Likely causes: bad map origin/resolution, initial pose error, wheel slip.

Fix:

1. Re-publish initial pose (RViz).
2. Verify map YAML resolution & origin.
3. Remap space if environment changed substantially.

No detections

Likely causes: wrong model path, too-high confidence, poor lighting.

Fix:

1. Confirm model path in object_detector.py.
2. Lower conf to 0.4–0.5.
3. Improve lighting; ensure object is within 0.3–3.5m.

Robot stops too far/close to object

Likely causes: camera→base_link offset incorrect.

Fix:

1. Adjust CAMERA_TO_BASE_LINK in detector (e.g., 0.10–0.18m).
2. Recalibrate static TF and re-test.

Arm misses object / bad grip

Likely causes: pose mismatch vs. gripper reach, wrong pickup pose.

Fix:

1. Tweak pickup angles in pick_node.py (pickup joints).
2. Ensure approach leaves clearance (no base collision).
3. Slow joint speed a bit for accuracy (e.g., 30–40).

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🧰 Step‑by‑Step Solutions (Triage Playbooks)

1) Nav2 Fail → Fast Recovery

1. Ctrl+C all nodes.
2. Start map + Nav2 only; wait stable.
3. Publish initial pose (RViz or pose_setter.py).
4. Send a tiny test goal near the robot.
5. If OK, launch full stack.

2) YOLO/Depth Fail → Fast Recovery

1. Check topics exist (/camera/color/image_raw, /camera/depth/image_raw, /camera/color/camera_info).
2. Validate TF: camera_link → base_link exists.
3. Restart camera node; then restart detector.
4. If still flaky, reduce conf, verify exposure/lighting.

3) Arm Not Responding

1. Verify Wi‑Fi connection; ping IP.
2. Run pick_node standalone with m5_ip param.
3. Power-cycle arm; re-run launch.

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🛡 Prevention Strategies

• Staggered Launch: Use TimerAction gaps (Camera → Nav2 → Pose Setter → Mission Manager → RQT).
• Map Hygiene: Remap after hardware changes (camera height, LiDAR swap, furniture move).
• Stable TFs: Keep a single source of truth for camera_link ↔ base_link (static publisher), launched early.
• Resource Headroom: Avoid starting RViz, Foxglove, and heavy terminals all at once on the robot; use a remote machine when possible.
• Battery & Space: >50% charge; ensure clear space for 270° scans and arm motions.
• Model Management: Store trained weights with versioned folders; update object_detector.py path intentionally.

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🧪 Quick Health Commands

# Topics & rates
ros2 topic list
ros2 topic hz /camera/color/image_raw
ros2 topic echo /amcl_pose -n1

# Actions & services
ros2 action list | grep navigate
ros2 service list | grep costmap

# TF sanity check
ros2 run tf2_tools view_frames.py

# Logs with highlighting
ros2 launch nav_handler full_system.launch.py | grep -E "WARN|ERROR|FAIL|❌|🛑|❌|⚠️"

Tip

Keep a known-good mission.log from a successful run. Diff against it when things break to spot regressions fast.

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Next: 🧑‍💻 Developer's Corner