I’ve ran into a problem with a pid loop where I can set the requested value in the debugger window and it works just fine. However when I connect my vex joystick to it it drives for ever in one direction, until I input the opposite direction for twice as long as it has been driving in that direction… the code I use is below

```
float pid_Kp = 2.0;
float pid_Ki = 0.04;
float pid_Kd = 0.0;
#define PID_SENSOR_INDEX I2C_1
#define PID_SENSOR_SCALE 1
#define PID_MOTOR_INDEX port9
#define PID_MOTOR_SCALE -1/2.5
#define PID_DRIVE_MAX 63
#define PID_DRIVE_MIN (-63)
#define PID_INTEGRAL_LIMIT 50
static int pidRunning = 1;
static float pidRequestedValue;
/*-----------------------------------------------------------------------------*/
/* */
/* pid control task */
/* */
/*-----------------------------------------------------------------------------*/
task pidController()
{
float pidSensorCurrentValue;
float pidError;
float pidLastError;
float pidIntegral;
float pidDerivative;
float pidDrive;
// If we are using an encoder then clear it
if( SensorType PID_SENSOR_INDEX ] == sensorQuadEncoder )
SensorValue PID_SENSOR_INDEX ] = 0;
// Init the variables - thanks Glenn :)
pidLastError = 0;
pidIntegral = 0;
while( true )
{
// Is PID control active ?
if( pidRunning )
{
// Read the sensor value and scale
pidSensorCurrentValue = SensorValue PID_SENSOR_INDEX ] * PID_SENSOR_SCALE;
// calculate error
pidError = pidSensorCurrentValue - pidRequestedValue;
// integral - if Ki is not 0
if( pid_Ki != 0 )
{
// If we are inside controlable window then integrate the error
if( abs(pidError) < PID_INTEGRAL_LIMIT )
pidIntegral = pidIntegral + pidError;
else
pidIntegral = 0;
}
else
pidIntegral = 0;
// calculate the derivative
pidDerivative = pidError - pidLastError;
pidLastError = pidError;
// calculate drive
pidDrive = (pid_Kp * pidError) + (pid_Ki * pidIntegral) + (pid_Kd * pidDerivative);
// limit drive
if( pidDrive > PID_DRIVE_MAX )
pidDrive = PID_DRIVE_MAX;
if( pidDrive < PID_DRIVE_MIN )
pidDrive = PID_DRIVE_MIN;
// send to motor
motor PID_MOTOR_INDEX] = pidDrive * PID_MOTOR_SCALE;
}
else
{
// clear all
pidError = 0;
pidLastError = 0;
pidIntegral = 0;
pidDerivative = 0;
motor PID_MOTOR_INDEX] = 0;
}
// Run at 50Hz
wait1Msec( 25 );
}
}
/*-----------------------------------------------------------------------------*/
/* */
/* main task */
/* */
/*-----------------------------------------------------------------------------*/
task main()
{
// send the motor off somewhere
nMotorEncoder[port9]= 0;
// start the PID task
startTask( pidController); // use joystick to modify the requested position
wait1Msec(35);
while( true )
{
while (SensorValue[dgtl1])//<---- is for a button so that if it is not pressed the code will not run.
{
// maximum change for pidRequestedValue will be 127/4*20, around 640 counts per second
// free spinning motor is 100rmp so 1.67 rotations per second
// 1.67 * 360 counts is 600
pidRequestedValue = pidRequestedValue + (vexRT(Ch1)/4);
}
motor[port9] = 0;
}
wait1Msec(35);
}
```