from machine import Pin,PWM
from time import sleep_ms

S1 = PWM(Pin(18),freq = 50,duty = 128)

def rotate (servo,degree):
  servo.duty(int(degree*0.54+25.6))

t = 50

while 1:
  for i in range(0,180,2):
    rotate(S1,i)
    sleep_ms(t)

  for i in range(180,0,-2):
    rotate(S1,i)
    sleep_ms(t)