Stepper setSpeed 120x slower than programmed

[Jordan Watkins]

Working on making a very simple micrometer driver. I need to start with an initial speed and accelerate over time. Ran into a problem with it decelerating after going half the distance, so I've added a check statement and doubled the distance.

But my problem is that the given initial speed that I thought I set with setSpeed is about 120 times lower than what my measured value was. Is there something I missing in my code or some math that I'm not thinking about? The speeds should all be in steps/second and the acceleration in steps/second^2.

Any help would be great!

#include <AccelStepper.h>

// create an instance of the stepper class, specifying

// the number of steps of the motor and the pins it's

// attached to

AccelStepper stepper(4, 4, 5, 6, 7);

long checkdist = stepper.currentPosition();

void setup()

{

  Serial.begin(9600);

  Serial.println("Stepper test!");

  

  stepper.setMaxSpeed(0.36666667);

  stepper.setSpeed(0.06087957);

  stepper.setAcceleration(0.00002231);

}

void loop()

{

  checkdist = stepper.currentPosition();

  if(checkdist >= 2921){

    stepper.stop();

  }

  else

  {

    stepper.moveTo(6000);

    stepper.run();

  }

}

[gregor]

Hi,

http://www.airspayce.com/mikem/arduino/AccelStepper/classAccelStepper.html#ace236ede35f87c63d18da25810ec9736

Set the target position. The run() function will try to move the motor (at most one step per call) from the current position to the target position set by the most recent call to this function. Caution: moveTo() also recalculates the speed for the next step. If you are trying to use constant speed movements, you should call setSpeed() after calling moveTo().

this may be the cause of your problem. try this:

void setup()

{

 Serial.begin(9600);

 Serial.println("Stepper test!");

 

 stepper.setMaxSpeed(0.36666667);

 stepper.setAcceleration(0.00002231);

 stepper.moveTo(6000);

 stepper.setSpeed(0.06087957);

}

void loop()

{
  //slightly changed loop(), because stop() does not work that way and
  //calling moveTo() and stop() very often is not necessary and/or may
  //cause problems

  checkdist = stepper.currentPosition();

 if(checkdist < 2921){

   stepper.run();

 }

}

 

[Jordan Watkins]

gregor,

Thanks for the speedy reply. I implemented these changes and added a toggle switch to the code. I changed the final velocity to match the velocity that the motor should move at at its declared final position. I took another set of data and found that it's now only 9 times slower than what it should be. I will now check if increasing the final position and final speed affects the initial speed. Maybe if I set the final position and max velocity at large values it will more closely approximate what I want. Dropping a copy of the new code.

#include <AccelStepper.h>

// create an instance of the stepper 

// class and the pins it's attached to

AccelStepper stepper(4, 4, 5, 6, 7);

// Declarations

long checkdist = stepper.currentPosition();

int TGLPIN = 3;

void setup()

{

  // Digital Input

  pinMode(TGLPIN, INPUT);

  

  Serial.begin(9600);

  Serial.println("AccelStepper Micrometer");

  

  // set Max Speed and Acceleration

  stepper.setMaxSpeed(0.53333333);

  stepper.setAcceleration(0.00002231);

  // set final position and initial speed

  stepper.moveTo(6009);

  stepper.setSpeed(0.06087460);

}

void loop()

{

  checkdist = stepper.currentPosition();

  while(digitalRead(TGLPIN)==LOW){

    if(checkdist < 2921){

      stepper.run();

    }

  }

}

[Jordan Watkins]

Update:

Changing the maxspeed and moveto did not change the value of initial velocity. Will now try multiplying the setspeed (what i supposed as the initial speed) to 9 times larger and see if the effect is matched even if I don't understand why.

Code has not changed from previous iteration besides specific values of above mentioned variables.

[Jordan Watkins]

Update

Still no solution from what I understand. Here's what I tried:

	maxspeed	maxspeed	maxspeed	maxspeed	maxspeed
	0.97968568	0.97968568	0.97968568	0.97968568	0.97968568
	moveto	moveto	moveto	moveto	moveto
	21460	21460	21460	21460	21460
	setspeed	setspeed	setspeed	setspeed	setspeed
	0.558603907	0	0.0608746	0.03043730	0.30973925
	checkdist	checkdist	checkdist	checkdist	checkdist
	364	364	364	364	364
a	2.22442E-05	0	2.23317E-05	2.22142E-05	2.2225E-05
v	0.006731645	0	0.006446182	0.006857827	0.0068081

Setting the setspeed as a new value had little effect on the acceleration or initial velocity except when I set it to 0 which makes it not move either at all or at an extremely slow speed. Makes sense that the acceleration didn't change, but I'm clueless as to why I can't seem to get the initial speed to change. 

Any suggestions would be appreciated.

[Jordan Watkins]

I have found out that the setAcceleration value has a large effect on the initial velocity of the motor. 

Set Values
v    0.0000    0.1000    0.1000    0.1000

a    0.0000    0.0100    0.1000    1.0000

Measured Values

v    0.0000    0.1444    0.4801    1.3782

a    0.0000    0.0100    0.0993    1.0350

I must be missing something about the way the code works.