from machine import Pin, PWM
from time import sleep_ms

m1A = PWM(Pin(18), freq=100)
m1B = PWM(Pin(19), freq=100)

m2A = PWM(Pin(21), freq=100)
m2B = PWM(Pin(22), freq=100)

d = 65000

while True:
    m1A.duty_u16(d)
    m1B.duty_u16(0)

    m2A.duty_u16(d)
    m2B.duty_u16(0)
    sleep_ms(2000)

    m1A.duty_u16(0)
    m1B.duty_u16(d)

    m2A.duty_u16(0)
    m2B.duty_u16(d)
    sleep_ms(2000)