motor does not move without Serial.println

Question

having strange behavior with motor shield and steppers. when i'm trying to make onestep, motor just makes some high-frequent noise, but when i add Serial.println for debugging, it moves as intended.

what is going on here?

here is an example:

#include AFMotor.h //dunno how to put angle brackets here

AF_Stepper lrM(48, 1);

void rightStep() {  
  lrM.onestep(BACKWARD, INTERLEAVE);
}
void leftStep() {  
  lrM.onestep(FORWARD, INTERLEAVE);
}

void setup() {
  Serial.begin(9600);
  Serial.println("ready");
}

void loop() {
  rightStep();
//Serial.println("right");
}

Answer 1

My guess is Serial.println adds additional delay so stepper motor can react. Without it changes are way too fast (= high frequency noise) to do whole step.

Try to add delay(1); or more into the main loop.

Answer 2

When you have a Serial print statement running really quickly the output buffer will fill up and the print command will have to wait for there to be room; That causes the command to take a substantial amount of time to complete.

When the statement is missing, you loop probably runs a few hundred times faster than without it (depending on how long onestep takes), probably fast enough that the physical motor can not keep up.

Try adding a delay of a few milliseconds or some kind of rate limiting to the program and then see how much of a difference serial.println makes.