Arduio + Pololu A4988 error???

Hi All

I have 2 Pololu A4988 and two NEMA17 (Spec: 5V, 1.2A) but i can’t control them with 5V only with 6V but the motors are shaking…

What can i do?
I hava a RAMS 1.4 can it solve the problem and it would be enough 5V, 2A as power supply for the board?

Circuit:
https://drive.google.com/file/d/0B8pthQnh7lw5UGNzUGpvZFRqY2s/edit?usp=sharing

Arduino Code:

// MultiStepper.pde
// -- mode: C++ --
//
// Shows how to multiple simultaneous steppers
// Runs one stepper forwards and backwards, accelerating and decelerating
// at the limits. Runs other steppers at the same time
//
// Copyright (C) 2009 Mike McCauley
// $Id: MultiStepper.pde,v 1.1 2011/01/05 01:51:01 mikem Exp mikem $

#include <AccelStepper.h>

// Define some steppers and the pins the will use
AccelStepper stepper1; // Defaults to AccelStepper::FULL4WIRE (4 pins) on 2, 3, 4, 5
AccelStepper stepper2(AccelStepper::FULL4WIRE, 6, 7, 8, 9);
AccelStepper stepper3(AccelStepper::FULL2WIRE, 10, 11);

void setup()
{
stepper1.setMaxSpeed(200.0);
stepper1.setAcceleration(100.0);
stepper1.moveTo(24);

stepper2.setMaxSpeed(300.0);
stepper2.setAcceleration(100.0);
stepper2.moveTo(1000000);

stepper3.setMaxSpeed(300.0);
stepper3.setAcceleration(100.0);
stepper3.moveTo(1000000);
}

void loop()
{
// Change direction at the limits
if (stepper1.distanceToGo() == 0)
stepper1.moveTo(-stepper1.currentPosition());
stepper1.run();
stepper2.run();
stepper3.run();

See my response on the Pololu forum: http://forum.pololu.com/viewtopic.php?f=15&t=8597