void go(int m1, int m2){
  m1=constrain(m1,-255,255);
  m2=constrain(m2,-255,255);
  if(m1 >= 0){
    digitalWrite(4,1);
  }else{
    digitalWrite(4,0);
    m1*=-1;
  }
  analogWrite(5,m1);
  if(m2 >= 0){
    digitalWrite(7,1);
  }else{
    digitalWrite(7,0);
    m2*=-1;
  }
  analogWrite(6,m2);
}