Different A4988 stepper drivers give different results

Other Hardware General Electronics
1

Hello,

I use an Arduino Uno R3, a stepper motor and 2 different A4988 drivers. A Big Easy driver and a cheap driver that has GY-4988 written on it. The Big Easy works exactly how I want and the torque is very good.

My problem is with the GY-4988. It only works in full step resolution and the motor has almost no torque. If I wire the MS pins to the VDD, the motor stops and vibrates. It feels like it is going one step in one direction and the next one in the opposite direction. If I wire the MS pins to GND, nothing happens and the motor works at full step.

I would like to make the cheap driver work like the Big Easy. 1/16th with the torque the Big Easy has.

I am using this code for testing

void setup() {                

  pinMode(8, OUTPUT);     

  pinMode(9, OUTPUT);

  digitalWrite(8, LOW);

  digitalWrite(9, LOW);

}


void loop() {

  digitalWrite(9, HIGH);

  delay(1);          

  digitalWrite(9, LOW); 

  delay(1);          

}

If I press the arduino reset button with the Big Easy, the motor stops and if I release the reset button it starts spinning normally. With the GY-4988, when I press the reset button the motor stutters a bit and when I release it, it spins in the opposite direction. Also, with the GY-4988 I can change the spinning direction by simply turning the motor shaft with my hand.

Another difference is when I power the driver but don't power the Arduino. The Big Easy holds the shaft in place and I can't spin it with my hand. The GY-4988 does not. It's like the motor is not connected to anything.

I wired the GY-4988 like this:

Also, it seems that the step and dir pins have to be reversed with the 2 drivers. Step on the GY-4988 is dir on the Big Easy and Dir on the Gy-4988 is Step on the Big Easy (this info I am not 100% sure about).

2

Have you checked the windings are wired up correctly?

Setting the EasyDriver to whole-steps so it matches the GY-4988 should give
similar performance - if not something is up (perhaps the cheap driver
is a factory-reject? There's a lot of this about from china on eBay).

Oh yes, does the cheap board allow the current to be set - if the current
isn't set the same as the EasyDriver then it is clearly going to perform
differently.

3

use the onboard potmeter to adjust current (incr/decr. torqe)

4

Have you definitely got the motor coils wired up right?

Remember that on the easy driver, one coil connects to A and the other to B.
On the Pololu board, one coil connects to 1A/1B, the other connects to 2A/2B