#include <Stepper.h>

const int stepsPerRevolution=200;

Stepper stepper1(stepsPerRevolution,18,19,21,22);
Stepper stepper2(stepsPerRevolution,13,122,14,27);

void setup(){
  stepper1.setSpeed(20);
  stepper2.setSpeed(20);

  Serial.begin(9600);
}

void loop(){
  if(Serial.available()>0){
    char direction=Serial.read();

    if(direction=='c'){
      stepper1.step(stepsPerRevolution);
      stepper2.step(stepsPerRevolution);
    }
    else if(direction='a'){
      stepper1.step(-stepsPerRevolution);
      stepper2.step(-stepsPerRevolution);
    }
  }
}