4. Safety & Operational Protocol

4.1 Sensors-Based Safety Layers

The Turtlebot 4 uses multiple redundant sensing layers to maintain safe operation in dynamic warehouse environments.

• Lidar Snesor: React to an obstacle detected within a specific range.
• Bump Sensor: Pause movement when hitting obstacles.
• Cliff Sensor: Prevent falling off a plane.
• Wheel-drop Sensor: Stop the wheel if the turtlebot is lifted.
• IMU: Monitors abnormal tilt, acceleration, or impacts.

4.2 Pysical Contraints

Physical contraints describe the non-negotiable real-world limits that the Turtlebots must abide to ensure safe and predictable behavior.

• Turtlebot Dimensions: The body frame size of the Turtlebot 4 and how the sensors are mounted have defines the safety distance to navigate without scraping pallets or shelving.
• Speed Limits: The robot must cap linear and angular velocity. The speed limits is directly tied to how fast the sensors can update and how far the robot need to stop.

4.3 Software Deadman Switch

The Deadman Switch ensures if the safety conditions are not met, the robot immediately halts all motion, cancels navigation goals, and requires manual reset.

• Message Timer: Missing /cmd_vel messages within 500ms halt the operation.
• Missing OOI: OOI is not detected beyond a threshold
• Battery Life Prediction: Halt the program when robots meet minimum battery threshold

4.4 Timeout Logic

Timeouts Logic decides when the robot must stop, slow down, or switch into a different mode because a critical subsystem no longer work reliably.

• Sensor Timeouts: Stop is missing Lidar/IMU/odom messages.
• Tracking Timeouts: Enters “search” or “safe fallback” mode when OOI lost beyond threshold.
• Planning Timeouts: Each operation is time-limited. Report the result(fail/succeed)
• Slow Update Speed: Low message/sensor update rate slows robot speed.

4.5 Emergency Stop(E-Stop) Conditions

The E-Stop defines the highest-priority safety mechanism. It forces irreversible motor shutdown until a human operator manually resets the system.

The E-Stop happens when:

• Wheel-drop triggered.
• Cliff sensor triggered.
• Bumper triggered.
• IMU tilted beyond safe limits.
• Extremely low battery level detected.
• Manual stop triggered by operators.

E-Stop behavior:

• Motors disabled
• Navigation goals canceled
• No autonomous recovery until manual reset