#include <Servo.h>

Servo servo1;
Servo servo2;

void setup() {
  servo1.attach(9);
  servo2.attach(10);
  Serial.begin(9600);
  Serial.print("format : [0-180][ab]");
}

void loop() {
  static int v = 0;

  if ( Serial.available() ) {
    char ch = Serial.read();

    switch(ch) {
      case '0'...'9':
        v = v * 10 + ch - '0';
        break;
      case 'a':
        servo1.write(v);
        v = 0;
        break;
      case 'b':
        servo2.write(v);
        v = 0;
        break;
    }
  }
}