Watchdog timer
A hardware or software timer that resets or triggers a safe-state action if not periodically refreshed by the running program. In the co-processor architecture, the microcontroller implements a watchdog on the SBC communication link: if no setpoint is received within the timeout window, the MCU enters a safe state and waits. Three safe-state patterns are in common use, and the correct choice depends on the robot's physical dynamics: (1) Torque-off / coast: the MCU disables motor driver enable signals, removing drive current and allowing the mechanism to coast to rest; appropriate for wheeled mobile robots on flat ground where coasting to a stop is safe. (2) Active braking: the MCU commands zero velocity to the motor driver while keeping the driver enabled, actively decelerating the mechanism; appropriate when a coasting mobile robot could roll into a hazard or when a moving arm must decelerate under control. (3) Hold-last-safe position: the MCU freezes its output at the last known-safe setpoint, keeping a joint or end-effector stationary; appropriate for collaborative arms holding a part, where dropping the load is more dangerous than remaining stationary. After the watchdog fires, the MCU must also implement a re-arm handshake before accepting new setpoints: it should require at least one valid setpoint message from the SBC (confirming the SBC has recovered) before exiting the safe state, rather than automatically resuming motion the moment any message arrives. A common pattern is to require a specific "resume" command or a sequence of zero-velocity setpoints before restoring normal motion, preventing a half-initialized SBC from issuing stale high-speed commands on first reconnect.
Defined in 2 GAGE programs, which carry 4 distinct definitions of it. The wording above is taught in Foundations of Robotics and Physical AI.
How each discipline defines it
The same term does different work depending on who is using it. These are the definitions as each program teaches them, unedited.
A hardware or software timer that resets or triggers a safe-state action if not periodically refreshed by the running program. In the co-processor architecture, the microcontroller implements a watchdog on the SBC communication link: if no setpoint is received within the timeout window, the MCU enters a safe state and waits. Three safe-state patterns are in common use, and the correct choice depends on the robot's physical dynamics: (1) Torque-off / coast: the MCU disables motor driver enable signals, removing drive current and allowing the mechanism to coast to rest; appropriate for wheeled mobile robots on flat ground where coasting to a stop is safe. (2) Active braking: the MCU commands zero velocity to the motor driver while keeping the driver enabled, actively decelerating the mechanism; appropriate when a coasting mobile robot could roll into a hazard or when a moving arm must decelerate under control. (3) Hold-last-safe position: the MCU freezes its output at the last known-safe setpoint, keeping a joint or end-effector stationary; appropriate for collaborative arms holding a part, where dropping the load is more dangerous than remaining stationary. After the watchdog fires, the MCU must also implement a re-arm handshake before accepting new setpoints: it should require at least one valid setpoint message from the SBC (confirming the SBC has recovered) before exiting the safe state, rather than automatically resuming motion the moment any message arrives. A common pattern is to require a specific "resume" command or a sequence of zero-velocity setpoints before restoring normal motion, preventing a half-initialized SBC from issuing stale high-speed commands on first reconnect.
An independent hardware or software mechanism that monitors whether a system is behaving as expected (for example, whether a compute subsystem is still responding) and takes a defined safe action, such as a reset or a controlled stop, if it is not. A watchdog timer is a common engineering response to a tightly coupled interface where one subsystem's failure could otherwise propagate silently into another.
A hardware or software timer that triggers a safety action, typically an emergency stop, if it is not reset within a specified period. Used to detect controller failures. A watchdog timer set at 5 milliseconds will trigger if no control command arrives within 5 milliseconds of the previous one.
A hardware or software mechanism that expects periodic confirmation signals ("heartbeats") from a monitored process or circuit; if the expected signal fails to arrive within a set time window, the watchdog assumes a fault has occurred and triggers a defined safe response.
Terms it appears with
Not an alphabetical neighbourhood: these are the terms taught in the same lessons, ranked by how often they appear together.