Overview

The null primitive does not perform any motion.  It enables the monitor to keep track of obstructions, edges, stalls, and other boundary conditions.  While this primitive is running, a user may update the speed via the damped-speed-left and damped-speed-right properties to drive the robot.  This primitive uses the velocity damping feature to make smooth transitions between different velocity settings.

If the null primitive detects a zero speed input, it will not check any sensors for boundary conditions.  When it detects a speed input that would create a net forward velocity, it checks the front rangers for collisions and checks the downward-looking edge sensors for dropoffs.  When it detects a speed input that would create a net reverse velocity, it checks the rear rangers for collisions.  Thresholds for front and rear obstacle detection may be adjusted by modifying the front-ranger-threshold and rear-ranger-threshold properties of the Garcia object.  These properties may also be set within an XML script by using a global primitive.

The null primitive terminates when it detects an end condition.  It overrides any additional speed commands and stops the motors.  It is up to the user to re-launch the primitive and provide a speed input that will make the robot move out of the situation that caused the end condition.

Return Status

This primitive exits when it detects a boundary condition that requires the robot to stop.  It returns an error value that indicates which sensor detected an end condition.

Property Inheritance

null inherits Behavior inherits Object properties.