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ExcelStepper

An excellent Arduino library for stepper motor control, offering simplicity, speed, and precise acceleration for smooth movement.

Features

  • Acceleration between speeds within a given distance
  • Jump between speeds
  • Faster speeds thanks to low computations
  • Non-blocking for multitasking
  • Multiple steppers

Usage

#include <ExcelStepper.h>

ExcelStepper stepper(2, 5);  // Create a new stepper motor on pins 2 and 5.

void setup() {
    Serial.begin(115200);

    stepper.begin();                                       // Set up the stepper motor.
    stepper.setDirection(ExcelStepper::COUNTERCLOCKWISE);  // Set the direction of the motor.
}

void loop() {
    stepper.accelerate(800, 500);  // Accelerates from 0 to 800 steps per second in 500 steps.
    stepper.runToTarget();         // Waits for the motor to reach 500 steps.

    stepper.move(500);  // Moves 500 steps at 800 steps per second.

    while (!stepper.run()) {                      // Loops until the motor has reached the target position.
        Serial.println(stepper.currentSpeed());  // Large computations like serial prints may slow down the motor.
    }

    // Accelerate from 800 to 1600 steps per second in 500 steps.
    stepper.accelerate(1600, 500);
    stepper.runToTarget();

    // Jump from 1600 to 800 steps per second.
    stepper.jumpToSpeed(800);
    stepper.move(500);
    stepper.runToTarget();

    // Decelerate to 0 steps per second in 1000 steps.
    stepper.decelerate(0, 1000);
    stepper.runToTarget();

    delay(1000);
}

Limitations

  • To improve speed, ExcelStepper only checks for existing PWM timers on the step pin in begin(). Use with caution!
  • Jumping to high speeds may not work due to physics. Use acceleration in such cases.
  • Slow accelerations from standstill may not work due to physics. Here are possible solutions:
    • Set a higher minumum speed. 
      ExcelStepper stepper(2, 5, YOUR_MIN_SPEED);
    • Split your sequence into multiple accelerations where the first is the highest.
    • A mixture of both.
  • In order to reduce computation time, changes in acceleration are not smooth. But see for yourself in the charts below.
  • ExcelStepper uses micros() for exact timing. micros() resets after about 70 minutes which may cause a step to trigger too soon.

Charts

The following charts were created using this demo sequence and a minimum speed of 100 steps/s:

#include "ExcelStepper.h"

ExcelStepper stepper(2, 5, 100);

void setup() {
    stepper.begin();

    stepper.accelerate(500, 500);
    stepper.runToTarget();

    stepper.move(500);
    stepper.runToTarget();

    stepper.decelerate(0, 500);
    stepper.runToTarget();
}

Velocity over distance

Stepper Motor Control Chart

Velocity over time

Stepper Motor Control Chart

Details

Minimum Speed Constraints

At very low speeds, intervals between steps become long. For instance, a speed of 0 steps per second would require an infinite interval. Additionally, motors have a minimum operational speed below which they cannot function properly. To ensure reliability, we calculate speed such that it never drops below this minimum threshold. To stop the motor, we simply stop triggering steps.

You can set the minSpeed in the constructor:

ExcelStepper stepper(2, 5, YOUR_MIN_SPEED);

How We Increased Speed Efficiency

Minimizing Float Usage

Floating-point operations are computationally expensive. By limiting precision to two decimal places, we can multiply values by 100 and work with integers, significantly improving performance.

Reducing Computation in run()

To streamline run(), we calculate acceleration only once, when accelerate() is called. In run(), speed is updated using a straightforward formula:

speed = targetSpeed - (acceleration x stepsRemaining) / 100

(where all variables are integers)

This ensures the target speed is achieved within the specified number of steps, even if step intervals are slightly imprecise. Although this approach appears to implement constant acceleration, intervals between steps naturally decrease as speed increases.

Optimizing digitalWrite() by Eliminating Redundant Checks

The Arduino digitalWrite() function includes several safety checks that ensure versatility but can slow down execution. By carefully removing certain checks that aren't essential for our specific application, we can improve performance.

For instance, digitalWrite() includes a check to determine if the pin is configured for PWM. Since we assume the user will not enable PWM on a motor control pin, this check can be moved to the begin() function. By handling it once during initialization, we can safely bypass it in digitalWrite(), significantly improving the function's execution speed.

Additionally, digitalWrite() repeatedly fetches the port and bit for the pin on each call. To streamline this, we can retrieve and store these values in the begin() function, reducing repetitive lookups and further optimizing execution speed.

We wrote another library to achieve this called FastPin.

Contributions Welcome

We're open to contributions, especially for improvements in speed and efficiency. Feel free to open issues or pull requests with optimizations, feature requests, or bug reports to help make this project even better. Your input is valuable and appreciated!