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1  Forum 2005-2010 (read only) / Interfacing / S-Curve for EasyDriver v3 Stepper Motor Driver on: January 13, 2009, 11:59:40 pm
I have an Arduino project where I'd like to control a stepper motor.  Unfortunately, the Arduino library for stepper motors is very limited.  I'd like to define parameters for the acceleration, deceleration, and total displacement and have the Arduino take care of the rest.  Poking around on this forum, I surprised that no one seems to have posted anything relating to this - so I figured it was incumbent on me to get something started.  I've attached my first iteration.  Seems to be working well in my tests.  Comments and suggestions will be greatly appreciated.

In my current setup, I'm using the EasyDriver stepper driver from sparkfun Electronics - though any driver that used pulse and direction should work fine.


=       Project: S curve
=      Language: Arduiino r12
=          Date: January 2008
=        Author: C. Eckert

// Givens
long ta = 3e6;     // acceleration time (microsec)
long td = 3e6;     // decelleration time (microsec)
long Vm = 3200;    // steady state velocity (pulse/sec)
long Pt = 12800;    // total number of pulses for move (1600 steps per rev)

// Other variables
long dly;           // stepper pulse delay (microsec)
long t = td/9;      // current time (microsec)  -  You need to seed the initial time with something > 0
                    //                             so you don't calculate to long of a delay
long t12;           // time during constant velocity (microsec)

int count = 0;      // count the number of pulses
int Perr = 0;       // error in position

// Arduino pins
#define dirPin 3
#define stepPin 12

void setup() {
  pinMode(dirPin, OUTPUT);
  pinMode(stepPin, OUTPUT);
  // Calculate the time at constant velocity
  t12 = (Pt/(Vm/1e6))-0.5*(ta+td);
  Serial.println(); Serial.println();

  Serial.println("Setup Done");
void loop()
  digitalWrite(dirPin, LOW);  // Set the stepper direction

  // Decide which part of the velocity curve your at
  if (t<ta) {                                       // Acceleration
    //Serial.println ("Acceleration Curve");
    dly = (ta)/(2*(Vm/1e6)*t);
  else if (t>=ta && t<(ta+t12)){                    // Constant velocity
    //Serial.println ("Constant Velocity");
    dly = 1/(2*(Vm/1e6));
  else if (t>=(ta+t12) && t<(ta+t12+td)){          // Deceleration
    //Serial.println ("Deceleration Curve");
    dly = 1/(2*((Vm/1e6)-(Vm/(1e6*td))*(t-ta-t12)));
  t = t+2*dly; // update the current time
  //Serial.print("dly: "); Serial.print (dly); Serial.println(" microsec");
  //Serial.print ("Current time: "); Serial.print(t); Serial.println(" microsec");
  // Move stepper one pulse using delay just calculated
  digitalWrite(stepPin, HIGH);
  digitalWrite(stepPin, LOW);
  count ++;
  // The move is finished
  if (t>(ta+t12+td)){
    Serial.println ("Move Complete");
    Serial.print ("Total steps indexed: "); Serial.println (count);
    // Correct for any position error due to rounding
    Perr = Pt-count;
    if (Perr < 0) {
      digitalWrite(dirPin, 1^digitalRead(dirPin));  // reverse the stepper direction
      Perr = -1*Perr;
    for (;Perr>0;){
      digitalWrite(stepPin, HIGH);
      digitalWrite(stepPin, LOW);
    delay (1000);

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