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");
}

• KIIV: We need Minimal, Complete, and Verifiable example
• curly brace: ok. i've added one, but it is very common usage

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.

• curly brace: i thought that if onestep function is blocking, it would be ok, but it appeared that i need delay(10) so that motor can run. thank you!
• KIIV: Method step contains delays, but there are no delays in onestep (at least not obvious ones).

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.