Speed up and slow down motors, then reverse.

SketchExtra.ino

/*
 * Author: Ratchanan Srirattanamet
 */

int Menable = 6; //PWM capable
int MdriveA = 5;
int MdriveB = 4;
int delaytime = 300;

void setup() {
  pinMode(Menable, OUTPUT);
  pinMode(MdriveA, OUTPUT);
  pinMode(MdriveB, OUTPUT);
  Serial.begin(9600);
}

void DriveMotCW(int Mspeed) {
  analogWrite(Menable, Mspeed);
  digitalWrite(MdriveA, 0);
  digitalWrite(MdriveB, 1);
}

void DriveMotCCW(int Mspeed) {
  analogWrite(Menable, Mspeed);
  digitalWrite(MdriveA, 1);
  digitalWrite(MdriveB, 0);
}

void loop() {
  int Mspeed = 0;
  
  for (Mspeed = 5; Mspeed <= 250; Mspeed += 5) {
    DriveMotCW(Mspeed);
    Serial.println(Mspeed);
    delay(delaytime);
  }
  for (Mspeed = 245; Mspeed >= 5; Mspeed -= 5) {
    DriveMotCW(Mspeed);
    Serial.println(Mspeed);
    delay(delaytime);
  }
    
  for (Mspeed = 5; Mspeed <= 250; Mspeed += 5) {
    DriveMotCCW(Mspeed);
    Serial.println(-Mspeed);
    delay(delaytime);
  }
  for (Mspeed = 245; Mspeed >= 5; Mspeed -= 5) {
    DriveMotCCW(Mspeed);
    Serial.println(-Mspeed);
    delay(delaytime);
  }
}