Page 280 ·
Robotics with the Boe-Bot
System
Error = -2
Kp X error
-35 X -2
Center pulse width
750
Output
adjust
+70
Left servo
output
820
Measured left
distance = 4
-
+
+
+
Figure 8-5
Proportional
Control Block
Diagram for
Left Servo and
IR LED and
Detector Pair
Programming the Boe-Bot Shadow Vehicle
Remember that the equation for the right servo’s output was:
Right servo output
=
(Right distance set point – Measured right distance)
×
Kp
+ Center pulse width
Here is an example of solving this same equation in PBASIC. The right distance set
point is 2, the measured distance is a variable named
distanceRight
that will store the
IR distance measurement, Kp is 35, and the center pulse width is 750:
pulseRight = 2 - distanceRight * 35 + 750
Remember that in PBASIC math expressions are executed from left to right.
First,
distanceRight
is subtracted from
2
. The result of this subtraction is then multiplied by
Kpr
, and after that, the product is added to the center pulse width.
You can use parentheses to force a calculation that is further to the right in a line of
PBASIC code to be completed first.
Recall this example: you can rewrite this line of
PBASIC code:
pulseRight = 2 - distanceRight * 35 + 750
like this:
pulseRight = 35 * (2 – distanceRight) + 750
In this expression, 35 is multiplied by the result of (
2 – distanceRight
), then the product is
added to 750.
