Problem Description:
I'm controlling two NEMA 17 stepper motors with A4988 drivers and an Arduino Uno. I'm experiencing a peculiar issue where one motor runs perfectly smooth during code upload but becomes erratic afterward, while the second motor works correctly in both scenarios.
The Specific Problem:
During upload: Both motors run smoothly
After upload:
Motor #1: Jerky, inconsistent movement, sometimes stalling or missing steps
Motor #2: Continues to work perfectly
The same code produces different behaviors between the two motors
Hardware Setup:
- Arduino Uno
- Two A4988 drivers (one for each motor)
- Two NEMA 17 stepper motors (identical models)
- Power Supply: 19V, 3.42A (both motors connected in parallel)
- USB power from computer during programming
Circuit Configuration:
- 19V, 3.42A Power Supply
- A4988 #1 ── NEMA 17 #1 (problematic)
- A4988 #2 ── NEMA 17 #2 (working correctly)
What I've Tried:
-
Verified power supply - 19V, 3.42A should be sufficient for both motors
-
Added decoupling capacitors (470µF) near each A4988
-
Verified all connections - No loose wires or poor connections
-
Added proper initialization in setup()
Current Code:
#include <Arduino.h>
#include <AccelStepper.h>
const int STEPA = 3;
const int DIRA = 4;
const int ENA = 2;
const int STEPB = 13;
const int DIRB = 8;
const int ENB = 12;
// const int EM = 8;
#define motorInterfaceType 1
AccelStepper StepperA(motorInterfaceType, STEPA, DIRA);
AccelStepper StepperB(motorInterfaceType, STEPB, DIRB);
void setup() {
Serial.begin(115200);
//pinMode(EM, OUTPUT);
pinMode(ENA, OUTPUT);
pinMode(ENB, OUTPUT);
StepperA.setMaxSpeed(2500);
StepperA.setAcceleration(100);
StepperA.setSpeed(2000);
StepperB.setMaxSpeed(2000);
StepperB.setAcceleration(100);
StepperB.setSpeed(2500);
digitalWrite(ENA, HIGH);
digitalWrite(ENB, HIGH);
}
int prev_place[] = {0, 0};
bool running = true;
void loop() {
// ALWAYS RUN THE MOTORS
StepperA.run();
StepperB.run();
// Only read commands when motors are idle
if (StepperA.distanceToGo() == 0 && StepperB.distanceToGo() == 0) {
digitalWrite(ENA, HIGH);
digitalWrite(ENB, HIGH);
if (Serial.available() > 0) {
String cmd = Serial.readStringUntil('\n');
cmd.trim();
int dx = 0;
int dy = 0;
if (cmd == "F") { dx = 0; dy = 200; }
else if (cmd == "B") { dx = 0; dy = -200; }
else if (cmd == "R") { dx = 200; dy = 0; }
else if (cmd == "L") { dx = -200;dy = 0; }
else if (cmd == "D1") { dx = -100;dy = 100; }
else if (cmd == "D2") { dx = 1000;dy = 1000; }
else if (cmd == "Q") { StepperA.stop(); StepperB.stop();}
int da = dx + dy;
int db = dx - dy;
// Serial.write);
if(da>0 || da<0){
digitalWrite(ENA, LOW);
}
if(db>0 || db<0){
digitalWrite(ENB, LOW);
}
int dadeg = (36 * da) / (10 * PI);
int dbdeg = (36 * db) / (10 * PI);
Serial.print(dadeg*10000);
StepperA.move(dadeg / 1.8);
StepperB.move(dbdeg / 1.8);
}
}
}
Key Observations:
Power: 19V should be within A4988 specs (8-35V), 3.42A should be enough for two motors
During upload: Both motors work perfectly (as a matter of fact, i don't why they move while code is being uploaded)
After upload: Only one motor becomes problematic
The problematic motor/driver combination is consistent (problem follows the specific A4988)
Current sharing: Both VREF pots set to same voltage
Heating: Neither A4988 gets excessively hot
What is the issue and how to solve?
I am new to this forum and any advice would be appreciated!
BONUS CLUE: If I hold the reset button on the Arduino, for as long as I hold it, it keeps rotating the motors perfectly, when i leave it they stop. Also, they were working perfectly 3 days ago. We just plugged them in today and this problem occured.