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Robot Control
The Path Planning module generated a PLAN_ORIENTATION variable which tells us what direction the next
waypoint is from the current robot position. We need to approximately orient the robot to match that
direction.
Since we know the current robot orientation from the ANGLE variable which was renamed to robot_orientation
we can compare that variable with the PLAN_ORIENTATION variable to determine how to
turn the robot. Once the robot is in that general direction we can just move the robot
forward and repeat the checking process. This control logic is performed using a script entered in the VBScript module.
' define some constants to use for speed. Note that the boe-bot
' moves forward with left and right being opposite numbers (due
' to the flipping of the servos as part of the robot
' construction)
left_speed = 115
right_speed = 105
rev_left_speed = 105
rev_right_speed = 115
stopped = 110
' this is the orientation produced by the path_planning and the
' orientation we want the robot to be at
desiredOrientation = GetVariable("plan_orientation")
' but first check to see if we are running or have completed
' all waypoints.
' When all waypoints have been visited the plan_orientation
' becomes -1.
if GetVariable("interface_run") <> "1" or _
desiredOrientation = "-1" then
SetVariable "left_motor", stopped
SetVariable "right_motor", stopped
else
' get the current robot orientation
robotOrientation = GetVariable("robot_orientation")
' reduce the precision of each of the orientations to
' 20 degree increments otherwise the robot (not being
' perfect in its movements) will spend all its time aligning
' to a degree that it cannot achieve.
robotOrientation = CInt((robotOrientation / 20) ) * 20
desiredOrientation = CInt((desiredOrientation / 20) ) * 20
' calculate the different between the two angles
diff = abs(desiredOrientation - robotOrientation )
' if they are the same (within 20 degrees) just
' move forward
if desiredOrientation = robotOrientation then
SetVariable "left_motor", left_speed
SetVariable "right_motor", right_speed
' otherwise turn in the appropriate direction. Note the use of
' 180 testing to determine which turn direction would
'be fastest.
' This allows the robot to turn in the most efficient direction
elseif desiredOrientation > robotOrientation and diff < 180 or _
desiredOrientation < robotOrientation and diff >= 180 then
SetVariable "left_motor", rev_left_speed
SetVariable "right_motor", right_speed
else
' if we don't turn one way then default to the other
SetVariable "left_motor", left_speed
SetVariable "right_motor", rev_right_speed
end if
end if ' interface_pause
At the end of this script the variables left_motor and right_motor contain the appropriate values to
send to the Parallax Boe-Bot.
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