Update stepper library: High-speed stepping mod and timer rollover fix

When using the stepper library with a 1.8 degrees per step motor, and at high angular speeds, the current Stepper library leads to really loud and jittery rotation. This is due to the fact that the timing is calculated in milliseconds, and the delay length between steps is only 2.5 milliseconds when trying to spin at 120 rpm. Since only integer math is performed, you end up actually bouncing between different step delays, and thus speeds, from step to step instead of giving the motor a constant input.  Which causes the motor to freak out.

Changing the library to calculate the step delays in micros() solves that problem for any speed you can reasonably demand from your stepper motor. The down side is that the micros() counter rolls over every hour or so, and any move you perform after that point will hang your code. Easy fix for that is to add an || micros() - this->last_step_time < 0 to the while loop if statement in Stepper.cpp.

Author: ekozlenko

libraries/Stepper/src/Stepper.cpp

@@ -5,6 +5,7 @@
   Two-wire modifications   (0.2) by Sebastian Gassner
   Combination version   (0.3) by Tom Igoe and David Mellis
   Bug fix for four-wire   (0.4) by Tom Igoe, bug fix from Noah Shibley  
+  High-speed stepping mod and timer rollover fix   (0.5) by Eugene Kozlenko
 
   Drives a unipolar or bipolar stepper motor using  2 wires or 4 wires
 
@@ -18,7 +19,8 @@
   A slightly modified circuit around a Darlington transistor array or an L293 H-bridge
   connects to only 2 microcontroler pins, inverts the signals received,
   and delivers the 4 (2 plus 2 inverted ones) output signals required
-  for driving a stepper motor.
+  for driving a stepper motor. Similarly the Arduino motor shields 2 direction pins
+  may be used.
 
   The sequence of control signals for 4 control wires is as follows:
 
@@ -70,7 +72,7 @@ Stepper::Stepper(int number_of_steps, int motor_pin_1, int motor_pin_2)
   this->step_number = 0;      // which step the motor is on
   this->speed = 0;        // the motor speed, in revolutions per minute
   this->direction = 0;      // motor direction
-  this->last_step_time = 0;    // time stamp in ms of the last step taken
+  this->last_step_time = 0;    // time stamp in us of the last step taken
   this->number_of_steps = number_of_steps;    // total number of steps for this motor
 
   // Arduino pins for the motor control connection:
@@ -100,7 +102,7 @@ Stepper::Stepper(int number_of_steps, int motor_pin_1, int motor_pin_2, int moto
   this->step_number = 0;      // which step the motor is on
   this->speed = 0;        // the motor speed, in revolutions per minute
   this->direction = 0;      // motor direction
-  this->last_step_time = 0;    // time stamp in ms of the last step taken
+  this->last_step_time = 0;    // time stamp in us of the last step taken
   this->number_of_steps = number_of_steps;    // total number of steps for this motor
 
   // Arduino pins for the motor control connection:
@@ -125,7 +127,7 @@ Stepper::Stepper(int number_of_steps, int motor_pin_1, int motor_pin_2, int moto
 */
 void Stepper::setSpeed(long whatSpeed)
 {
-  this->step_delay = 60L * 1000L / this->number_of_steps / whatSpeed;
+  this->step_delay = 60L * 1000L * 1000L / this->number_of_steps / whatSpeed;
 }
 
 /*
@@ -144,9 +146,9 @@ void Stepper::step(int steps_to_move)
   // decrement the number of steps, moving one step each time:
   while(steps_left > 0) {
   // move only if the appropriate delay has passed:
-  if (millis() - this->last_step_time >= this->step_delay) {
+  if (micros() - this->last_step_time >= this->step_delay || micros() - this->last_step_time < 0) {
       // get the timeStamp of when you stepped:
-      this->last_step_time = millis();
+      this->last_step_time = micros();
       // increment or decrement the step number,
       // depending on direction:
       if (this->direction == 1) {
@@ -229,5 +231,5 @@ void Stepper::stepMotor(int thisStep)
 */
 int Stepper::version(void)
 {
-  return 4;
+  return 5;
 }