The way that most porcupines defend themselves from predators is by hiding its bare face from an attacker and keeping its bare belly to the ground.
If that is not enough for the porcupine to defend itself the porcupine will swat it's tail at whatever is trying to attack it.
The porcupines quails are not poisonous nor do they shoot out by the porcupines quails are helpful in defense as it makes it harder for predators to try and get near it or eat it.
The quails do however detach from the porcupine easily though and sometimes a porcupine may fall on it's own quails.
The porcupine rarely gets attacked or eaten because most predators would prefer to stay away from due to the quails.