Help!

[Duman017]

Hi,I need to increase my robot’s speed.So,can you help me?
I added to your code time.After time is end,robot stopped.And now I want in order to robot in some point increase his speed.Can you help?

#include <ZumoReflectanceSensorArray.h>
#include <ZumoMotors.h>
#include <ZumoBuzzer.h>
#include <Time.h>
#include <Pushbutton.h>



ZumoBuzzer buzzer;
ZumoReflectanceSensorArray reflectanceSensors;
ZumoMotors motors;
Pushbutton button(ZUMO_BUTTON);
int lastError = 0;

const int MAX_SPEED = 600;


void setup()
{
  buzzer.play(">g32>>c32");

  reflectanceSensors.init();

  button.waitForButton();

  pinMode(13, OUTPUT);
  digitalWrite(13, HIGH);

  delay(1000);
  int i;
  for(i = 0; i < 80; i++)
  {
    if ((i > 10 && i <= 30) || (i > 50 && i <= 70))
      motors.setSpeeds(-200, 200);
    else
      motors.setSpeeds(200, -200);
    reflectanceSensors.calibrate();

    delay(20);
  }
  motors.setSpeeds(0,0);

  digitalWrite(13, LOW);
  buzzer.play(">g32>>c32");

  button.waitForButton();

  buzzer.play("L16 cdegreg4");
  while(buzzer.isPlaying());
}
time_t t = now();
void loop()
{
  if(second(now() - t) >= 20.0) {
    motors.setSpeeds(0, 0);
    return;
  }
  unsigned int sensors[6];

  int position = reflectanceSensors.readLine(sensors);

  int error = position - 2500;

  int speedDifference = error / 4 + 6 * (error - lastError);

  lastError = error;

  int m1Speed = MAX_SPEED + speedDifference;
  int m2Speed = MAX_SPEED - speedDifference;

  if (m1Speed < 0)
    m1Speed = 0;
  if (m2Speed < 0)
    m2Speed = 0;
  if (m1Speed > MAX_SPEED)
    m1Speed = MAX_SPEED;
  if (m2Speed > MAX_SPEED)
    m2Speed = MAX_SPEED;

  motors.setSpeeds(m1Speed, m2Speed);
}