Cannot decelerate by lowering setMaxSpeed

[Michaël Bruneau]

I am trying to control the speed of a step motor using an acceleration and a Max Speed. 

If I increase the MaxSpeed, the motor accelerates smoothly, but if I lower the MaxSpeed, it does not decelerate, reaching right away the new lower speed.

If I Stop instead, the deceleration works normally to zero. Is there a way to decelerate without stopping?

Here is my test code:

#include <AccelStepper.h>
#include <elapsedMillis.h>

// Motor Connections (constant current, step/direction bipolar motor driver)
const int dirPin = 4;
const int stepPin = 3;

// Creates an instance
AccelStepper myStepper(AccelStepper::DRIVER, stepPin, dirPin);           // works for a4988 (Bipolar, constant current, step/direction driver)

elapsedMillis printTime;

void setup() {
  Serial.begin(115200);
  // set the maximum speed, acceleration factor, and the target position.
  myStepper.setMaxSpeed(0.0);   // the motor accelerates to this speed exactly without overshoot.
  myStepper.setAcceleration(4000.0);  
  myStepper.moveTo(48000);

}
int count = 0;    // tracks seconds to trigger an action if desired.
void loop() {
  float mSpeed;
  if (printTime >= 1000) {    
    printTime = 0;  

    switch (count++){
      case 1:
        myStepper.setMaxSpeed(4000.0);
        break;
      case 3:
        myStepper.setMaxSpeed(0.0);
        break;
      case 5:
        myStepper.setMaxSpeed(1500.0);
        break;
      case 7:
        myStepper.setMaxSpeed(4000.0);
        break;
      case 9:
        myStepper.stop();
        break;
    }
  }

Thanks in advance,

Michael

[gregor christandl]

Not in vanilla AccelStepper. But this is a common question, forks which support this should exist. 

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[Jim Larson]

Here is one way to do the requested action. Please note that I have provided code that uses speeds for my motor/driver combination. Also, the use of HardwareSerial won't be required for most Arduino or Arduino-like processors.

#include <AccelStepper.h>

#include <elapsedMillis.h>

// Motor Connections (constant current, step/direction bipolar motor driver)

const int dirPin = 16;

const int stepPin = 14;

AccelStepper myStepper(AccelStepper::DRIVER, stepPin, dirPin); // works for a4988 (Bipolar, constant current, step/direction driver)

HardwareSerial Serial(23, 24); // only needed for G431 // for G431

elapsedMillis printTime;

void setup() {

Serial.begin(115200);

myStepper.setMaxSpeed(0.0); // the motor accelerates to this speed exactly without overshoot.

myStepper.setAcceleration(400.0);

myStepper.moveTo(48000);

}

int count = 0; // tracks seconds to trigger an action if desired.

float targetSpeed = 0.0; // target speed to slow to.

bool slowing = false; // set this to do a slow down. Set targetSpeed first.

void loop() {

float mSpeed;

if (printTime >= 1000) {

printTime = 0;

switch (count++) {

case 1:

myStepper.setMaxSpeed(400.0);

break;

case 3:

targetSpeed = 100.0;

slowing = true;

myStepper.stop();

break;

case 5:

myStepper.setMaxSpeed(200.0);

break;

case 7:

myStepper.setMaxSpeed(400.0);

break;

case 9:

myStepper.stop();

break;

}

}

myStepper.run();

if (slowing) {

if (myStepper.speed() <= targetSpeed) {

myStepper.moveTo(48000);

myStepper.setMaxSpeed(targetSpeed);

slowing = false;

}

}

}

HTH

           -jim