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 transistor array.

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:

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.

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:

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

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

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

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).
    '''

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:

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:

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
    '''

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:

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

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

Check out the repo

me

The world is a complex puzzle, and I love using data and code to decode it. Data scientist and developer by day, problem-solver always.

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