Sensor disconnects intermittently

1. Symptoms

• The sensor disappears from the device list and comes back.
• The driver reports a timeout or an I/O error and stops publishing.
• It happens when motors start or the robot moves.

2. Possible causes

• Brown-out of the sensor’s supply when motors start.
• A loose or damaged connector or cable, or strain at a moving joint.
• An unpowered or overloaded USB hub or too many devices on one controller.
• Electrical interference on the cable.
• The device renumbering after a reset so the driver opens the wrong path.
• A driver that does not reopen after the device returns.

3. Measurements to collect

• Kernel log around each disconnect.
• Supply voltage at the sensor during an event.
• The device path before and after.

4. Diagnostic commands

Commands are not executed by the site’s automated tests (they need a ROS 2 Jazzy installation or the robot).

dmesg -w | grep -i -E "usb|disconnect|reset|ttyUSB|eth"
ls -l /dev/serial/by-id/
ros2 topic hz /scan

5. Step-by-step investigation

1. Read the kernel log at the disconnect time.
2. Correlate with events (motors starting, movement, temperature).
3. Measure the supply voltage during an event.
4. Swap the cable, port and hub one at a time.
5. Check the device name is stable and the driver reopens it.

6. Corrective actions

• Give the sensor a stable, separate supply; use a powered hub.
• Replace or re-route the cable; add strain relief.
• Use stable device names (by-id or udev rules).
• Make the driver detect silence and reopen with back-off (see the reliable driver guide).

7. Validation after the fix

• No disconnects in a long run with the motors active and the cable flexed as in service.

References

• See the reliable driver guide, the sensor connection guide and the data-drop page.