RPistepper

RPistepper

RPistepper is a library containing: * A class to control a stepper motor with a RPi. * A function to execute a zig-zag motion with two motors. * A function to execute a square_spiral motion with two motors.

Wiring

In our setup, the power to the motors (Vm) is supplied with the 5V pins of the RPi, the grounding of the coils is controlled with a ULN2803A <http://www.ti.com/lit/ds/symlink/uln2803a.pdf>__ transistor array.

.. figure:: pinout.png :alt: Example setup

Alt text

Conections RPi - ULN2803A: ^^^^^^^^^^^^^^^^^^^^^^^^^^

+-----------------+------------+ | RPi Pin (BCM) | ULN2803A | +=================+============+ | 17 | 1B | +-----------------+------------+ | 27 | 2B | +-----------------+------------+ | 10 | 3B | +-----------------+------------+ | 9 | 4B | +-----------------+------------+ | 14 | 5B | +-----------------+------------+ | 15 | 6B | +-----------------+------------+ | 23 | 7B | +-----------------+------------+ | 24 | 8B | +-----------------+------------+

Conections ULN2803A - Motors: ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

+------------+---------------------+ | ULN2803A | Motors | +============+=====================+ | 1C | Motor_1 Coil_A1 | +------------+---------------------+ | 2C | Motor_1 Coil_A2 | +------------+---------------------+ | 3C | Motor_1 Coil_B1 | +------------+---------------------+ | 4C | Motor_1 Coil_B2 | +------------+---------------------+ | 5C | Motor_2 Coil_A1 | +------------+---------------------+ | 6C | Motor_2 Coil_A2 | +------------+---------------------+ | 7C | Motor_2 Coil_B1 | +------------+---------------------+ | 8C | Motor_2 Coil_B2 | +------------+---------------------+

In this case, two motors were attached to the ULN2803A.

Usage

class Motor ^^^^^^^^^^^

This class allows the user to control a 6 pin stepper motor using 4 GPIO pins of a RPi.

Software uses BCM mode for pin indexing.

This class is best used with the 'with' statement to properly handle the cleanup of the GPIOs.

self.steps is a property of this class that will get the number of steps taken from the initial position or set to a specific step, similar to self.move.

In order to save power, it's advised to call self.release() when the motor is idle.

Arguments are a list with the 4 pins (Coil_A1, Coil_A2, Coil_B1, Coil_B2), the delay between steps (default = 20ms) and verbose to display reports on the motor movements, the last two are optional. e.g:

.. code:: python

import RPistepper as stp
M1_pins = [17, 27, 10, 9]
with stp.Motor(M1_pins) as M1:
    for i in range(10):               # moves 20 steps,release and wait
        print M1
        M1.move(20)
        M1.release()
        raw_input('enter to execute next step')

If the class is instantiated normally, use the method cleanup prior to closing the application to close the GPIO resources. Also, if it's important to go back to the initial position when finishing the routine, use the method reset.

.. code:: python

import RPistepper as stp
M1_pins = [17, 27, 10, 9]
M1 = stp.Motor(M1_pins)
for i in range(10):               # moves 20 steps,release and wait
    print M1
    M1.move(20)
    M1.release()
    raw_input('enter to execute next step')
M1.reset()
M1.cleanup()

Methods ^^^^^^^

Currently there are five implemented methods:

.. code:: python

def move(self, steps):
    '''
    Moves the motor 'steps' steps. Negative steps moves the motor backwards
    '''

.. code:: python

def release(self):
    '''
    Sets all pins low. Power saving mode
    '''

.. code:: python

def reset(self):
    '''
    Returns the motor to it's initial position
    '''

.. code:: python

def zero(self):
    '''
    Sets the motor to the next position which Coil_A1 and Coil_A2
    are on. Sets this position as the reference (steps = 0).
    '''

.. code:: python

def cleanup(self):
    '''
    Cleans the GPIO resources
    '''

The main method is move, which moves the motor the desired number of steps

steps property ^^^^^^^^^^^^^^

It's possible to check the motor position or manually set the desired step using the steps property:

.. code:: python

import RPistepper as stp
M1_pins = [17, 27, 10, 9]
with stp.Motor(M1_pins) as M1:
    for i in range(10):               # moves 20 steps,release and wait
        print M1.steps
        M1.steps = 20*i
        M1.release()
        raw_input('enter to execute next step')
    M1.reset()

Attributes ^^^^^^^^^^

This class haves the following attributes:

+-----------------+------------------------------------------------+ | Attribute | Data | +=================+================================================+ | DELAY | Time between steps | +-----------------+------------------------------------------------+ | VERBOSE | Display motor data on screen | +-----------------+------------------------------------------------+ | PINS | GPIOs used by the instance | +-----------------+------------------------------------------------+ | actual_state | A list with the status of the coils (on/off) | +-----------------+------------------------------------------------+

functions

These two functions executes pre determined movements and requires two
stepper motor objects:

.. code:: python

    def zig_zag(motor1, motor2, amp1, amp2, delay=None):
        '''
        Executes a zig-zag movement with two RPistepper objects.
        Arguments are: motor1 and motor2 objects and amp1, amp2, the amplitude
        of movement, a tuple (step, rep) representing the number of steps per
        iteration and the number of iterations of the following algorithm:
            Repeat rep1 times:
                1. Moves motor 2 step2*rep2 steps forward
                2. Moves motor 1 step1 steps forward
                3. Moves motor 2 step2*rep2 steps backwards
                4. Moves motor 1 step1 steps forward
            Reset to initial state
            Release the motors
        It's possible to change the delay between steps with the 'delay' argument
        '''

.. code:: python

    def square_spiral(motor1, motor2, amplitude, delay=None):
        '''
        Executes a square spiral movement with two RPistepper objects.
        Arguments are: motor1 and motor2 objects and the amplitude of movement,
        a tuple (step, rep) representing the number of steps per iteration and
        the number of iterations of the following algorithm:
            for i in range(rep):
                1. Moves motor 2 to position i
                2. Moves motor 1 to position i
                3. Moves motor 1 to position -i
                4. Moves motor 2 to position -i
            Reset to initial state
            Release the motors
        It's possible to change the delay between steps with the 'delay' argument
        '''

/bin/rpistepper
---------------

``rpistepper`` is a shell for controlling the motors. It provides all
the methods in the ``Motor`` class. All the commands are documented in
the shell. It's possible to pipe a list of commands to the shell:

.. code:: bash

    rpistepper < sample.stp
            or
    cat sample.stp | rpistepper

Invoking ``rpistepper`` with ``-g`` flag will open a GUI application
with similar functionality