Accelstepper.h library: 3 questions

Projects General Guidance
1

When reading the Accelstepper.h following lines appear (from 476 to 489):

    long    currentPosition();  

    /// Resets the current position of the motor, so that wherever the motor
    /// happens to be right now is considered to be the new 0 position. Useful
    /// for setting a zero position on a stepper after an initial hardware
    /// positioning move.
    /// Has the side effect of setting the current motor speed to 0.
    /// \param[in] position The position in steps of wherever the motor
    /// happens to be right now.
    void    setCurrentPosition(long position);  
    
    /// Moves the motor (with acceleration/deceleration)
    /// to the target position and blocks until it is at
    /// position. Dont use this in event loops, since it blocks.

However, in Accelstepper.cpp following shows (lines 82 to 95:

long AccelStepper::currentPosition()
{
    return _currentPos;
}

// Useful during initialisations or after initial positioning
// Sets speed to 0
void AccelStepper::setCurrentPosition(long position)
{
    _targetPos = _currentPos = position;
    _n = 0;
    _stepInterval = 0;
    _speed = 0.0;
}

  1. Rather than resetting the current position to the new 0 position, does currentPosition not return the actually stored current position?

  2. setCurrentPosition: can this not also be used to store a new value in setCurrentPosition? For example to assign a new value to currentPosition (without moving the stepper)

  3. If the latter is not true, how can (with this library) a new value be assigned the currentPosition? For example, on startup or reset of the program) to assign a value to the current position of the stepper. Such as if, before reset, a specific current stepper position needs to be restored after reset.

2

  1. mystepper.currentPosition() reports the current position, it might well have been named getCurrentPosition(), but was not. The get/set pair of accessor functions for the private variable _currentPos are currentPosition() and setCurrentPosition()

  2. is true. myStepper.setCurrentPosition(-1000); will change the current idea of its position to -1000. it can happen without stepper movement.

3 (2 is true) so you use setCurrentPosition to assign a new value.

3

Thanks f@DaveX or such a speedy reply!

"... it can happen without stepper movement..."

How to get the stepper not to move?

And what would make the stepper to move?

4

You get the stepper not to move by not telling it to move, or, if it is already in motion from a previous command, try .stop()

You make the stepper move by giving it a movement command.
https://www.airspayce.com/mikem/arduino/AccelStepper/classMultiStepper.html#a26c2f53b1e7ddf5d5dfb333f6fb7fb92

1 Like
5

Top! Thank you, understood.

6

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