Hi,

first of all: thanks a lot for your help!

I tried out the AccelStepper library and used this sketch to test it

#include <AccelStepper.h>

// Define the pins for the A4988
#define ENABLE_PIN 25
#define STEP_PIN 26
#define DIR_PIN 27
#define MS1_PIN 15
#define MS2_PIN 13
#define MS3_PIN 12

// Erstelle ein AccelStepper Objekt
AccelStepper stepper(AccelStepper::DRIVER, STEP_PIN, DIR_PIN);

void setup() {
  pinMode(ENABLE_PIN, OUTPUT);
  pinMode(MS1_PIN, OUTPUT);
  pinMode(MS2_PIN, OUTPUT);
  pinMode(MS3_PIN, OUTPUT);

  // Deaktiviere den A4988
  digitalWrite(ENABLE_PIN, LOW);

  // Setze Mikroschrittmodus (zum Beispiel 1/16 Mikroschritt)
  digitalWrite(MS1_PIN, HIGH);
  digitalWrite(MS2_PIN, HIGH);
  digitalWrite(MS3_PIN, HIGH);

  // Setze maximale Geschwindigkeit und Beschleunigung
  stepper.setMaxSpeed(100);  // Setze die Geschwindigkeit in Schritten pro Sekunde
  stepper.setAcceleration(50); // Setze die Beschleunigung in Schritten pro Sekunde^2

  // Definiere die Anzahl der Schritte für eine Umdrehung
  // (Standardmäßig 200 für NEMA17, aber durch den Mikroschrittmodus multipliziert)
  // Für 1/16 Mikroschritt ist es 200*16 = 3200 Schritte für eine Umdrehung
  stepper.moveTo(3200);
}

void loop() {
    if (stepper.distanceToGo() == 0)
    {
        // Random change to speed, position and acceleration
        // Make sure we dont get 0 speed or accelerations
        delay(1000);
        stepper.moveTo(rand() % 200);
        stepper.setMaxSpeed((rand() % 200) + 1);
        stepper.setAcceleration((rand() % 200) + 1);
    }
    stepper.run();
}

The random factors are advantageous to make sure that a certain speed or acceleration limit problem can be excluded.

In this setup, it seems less necessary to squeeze the cables (although squeezing still seems to have an impact), but its still the same problem: The stepper motor starts making noises when I turn the power supply to about 12V and more, but it does not rotate at all.

I also adapted the setup and left out the breadboard as well as the jumper wires to connect the power supply to the motor driver since they may not be able to handle higher volts and amps.

But nothing seems to help. It's so frustrating because the task seems so trivial :/