Driving the motors - PlayStation 3 (Python)

To more easily control and drive around the BigTrak you can connect up a PlayStation 3 DualShock controller and use it as a joystick from inside a Python script.

To keep things easy the pygame library can be used to talk to the joystick, this is installed by default on the latest Raspberry Pi disk images, so all you should need to do is download and run the script.

#!/usr/bin/env python

import pygame
import time
import RPi.GPIO as GPIO

# Initialise the pygame library
pygame.init()

# Connect to the first JoyStick
j = pygame.joystick.Joystick(0)
j.init()

print 'Initialized Joystick : %s' % j.get_name()

# Setup the various GPIO values, using the BCM numbers for now
DRIVEA0 = 25
DRIVEA1 = 4
STANDBY = 17
DRIVEB0 = 18
DRIVEB1 = 21
A0 = False
A1 = False
B0 = False
B1 = False

GPIO.setmode(GPIO.BCM)
GPIO.setup(DRIVEA0, GPIO.OUT)
GPIO.setup(DRIVEA1, GPIO.OUT)
GPIO.setup(STANDBY, GPIO.OUT)
GPIO.setup(DRIVEB0, GPIO.OUT)
GPIO.setup(DRIVEB1, GPIO.OUT)

# Set all the drives to 'off'
GPIO.output(DRIVEA0, A0)
GPIO.output(DRIVEA1, A1)
GPIO.output(STANDBY, False)
GPIO.output(DRIVEB0, B0)
GPIO.output(DRIVEB1, B1)

# Only start the motors when the inputs go above the following threshold
threshold = 0.60


LeftTrack = 0
RightTrack = 0

# Configure the motors to match the current settings.
def setmotors():
        GPIO.output(DRIVEA0, A0)
        GPIO.output(DRIVEA1, A1)
        GPIO.output(STANDBY, True)
        GPIO.output(DRIVEB0, B0)
        GPIO.output(DRIVEB1, B1)

# Try and run the main code, and in case of failure we can stop the motors
try:
    # Turn on the motors
    GPIO.output(STANDBY, True)

    # This is the main loop
    while True:

        # Check for any queued events and then process each one
        events = pygame.event.get()
        for event in events:
          UpdateMotors = 0

          # Check if one of the joysticks has moved
          if event.type == pygame.JOYAXISMOTION:
            if event.axis == 1:
              LeftTrack = event.value
              UpdateMotors = 1
            elif event.axis == 3:
              RightTrack = event.value
              UpdateMotors = 1

            # Check if we need to update what the motors are doing
            if UpdateMotors:

              # Check how to configure the left motor

              # Move forwards
              if (RightTrack > threshold):
                  A0 = False
                  A1 = True
              # Move backwards
              elif (RightTrack < -threshold):
                  A0 = True
                  A1 = False
              # Stopping
              else:
                  A0 = False
                  A1 = False

              # And do the same for the right motor
              if (LeftTrack > threshold):
                  B0 = False
                  B1 = True
              # Move backwards
              elif (LeftTrack < -threshold):
                  B0 = True
                  B1 = False
              # Otherwise stop
              else:
                  B0 = False
                  B1 = False

              # Now we've worked out what is going on we can tell the
              # motors what they need to do
              setmotors()


except KeyboardInterrupt:
    # Turn off the motors
    GPIO.output(STANDBY, False)
    j.quit()