Lesson-4.markdown

@@ -61,12 +61,22 @@ The program for this exercise implements a standard PID controller in the follow
 			
 // Apply the PID regulation
 controlledValue = (kp * error) + (ki * integral) + (kd * derivative);		
-			
 controlSignal(controlledValue);
 			
 lastError = error;			
-			
 Delay.msDelay(dt);
+````
+where the function controlSignal controls the power of the two motors in the following way
+```java
+protected void controlSignal(float controlledValue) {
+    leftMotor.controlMotor((int)(Tp + controlledValue),1);
+    rightMotor.controlMotor((int)(Tp - controlledValue),1);
+}
+````
+
+In order to avoid a bang-bang control mechanism the two motors are applied a standard power `Tp`.
+
+The control algorithm is wrapped in an LeJOS NXT application that is able to communicate with a PC running a LeJOS GUI application letting us choose values for `kp`,`ki`,`kd` and `Tp` remotely. Due to the complexity of the physical world many factors affect the controlling of the Lego car and it is therefore beneficial to modify control parameters on the fly.
 
 ### Exercise 6, Color Sensor