PS3 Controller to move a USB Robot Arm

Guest Blogger Hiren Mistry, Nuffield Research Placement Student working at the University of Northampton.

How to use a PS3 Controller to move a USB Robot Arm on a Raspberry Pi

By Hiren Mistry

This program enables the user to control the robot arm via a PlayStation 3 Controller, through USB connection.

Requirements:

·       PyUSB- This must be installed so the Python Code can interact with the USB Robot Arm. It can be downloaded from https://sourceforge.net/projects/pyusb/files/PyUSB%201.0/1.0.0/pyusb-1.0.0.tar.gz/download

·       PyGame- This module is needed to receive input from the PS3 controller. It can be downloaded from http://www.pygame.org/download.shtml 

How does it Work?

To receive the input from the controller PyGame is used. PyGame is a set of modules used for writing games and contains the necessary modules need to receive the PlayStation controller input.

The input consists of 3 major parts of the controller:

·       Buttons- These have a Boolean on/off state

·       Hats- These are digital inputs and return a 1 or 0. Hats tilt left/right or up/down.

·       Axis- These are your standard joysticks and return a value between 1 and -1. One joystick has two axes- up/down and left/right.

For my input, I have decided to use a combination of Buttons and Axis (Joysticks) to control the Robot Arm.

Image: This image has been modified from http://www.console.maban.co.uk/device/ps3. License:https://creativecommons.org/licenses/by-sa/3.0/legalcode

Next, I found out which input is assigned to which number which will enable me to move the arm once I have mapped each input.

Here are some commands:

Command	Explanation
pygame.joystick.init()	Initialize pygame to read controllers
pygame.joystick.get_count()	Get 1 joystick, number 0
pygame.joystick.Joystick(0)	Assign the first controller
joystick.init()	Initialize the first controller for reading
joystick.get_numaxes()	Return the number of axes on the controller
joystick.get_axis(axis_number)	Get the analogue value (float) of the specified axis
pygame.joystick.Joystick.get_button(i)	Returns the current state of a joystick button.
pygame.joystick.Joystick.quit	This will uninitialize the Joystick.

Axis Number

0 = Left joystick left to right values -1.0 to 1

1 = Left joystick up to down values -1.0 to 1

2 = Right joystick left to right values -1.0 to 1

3 = Right joystick up to down values -1.0 to 1

The picture above illustrates the axis value for each axis number depending on the position of the joystick. For example, if the left joystick was in the bottom left direction, then the axis numbers and values would be ‘Axis Number 0 = -1, Axis Number 1 = 1’.

Button Number

Button	Number	Button	Number
SELECT	0	R2	9
L3	1	L1	10
R3	2	R1	11
START	3	TRIANGLE	12
D-PAD UP	4	CIRCLE	13
D-PAD RIGHT	5	CROSS	14
D-PAD DOWN	6	SQUARE	15
D-PAD LEFT	7	PLAYSTATION LOGO	16
L2	8

Axis numbers and Button numbers were both found using the code below. This code prints the axis values (from -1 to 1) and Button States (1 or 0) if they are pressed. I would then press a button/move an axis and analyse the numbers produced. These may be different depending on how your controller is setup so I would recommend running the code below and test which buttons are assigned to which numbers.

import pygame, sys, time    #Imports Modules

from pygame.locals import *

pygame.init()#Initializes Pygame

pygame.joystick.init()

joystick = pygame.joystick.Joystick(0)

joystick.init()#Initializes Joystick

# get count of joysticks=1, axes=27, buttons=19 for DualShock 3

joystick_count = pygame.joystick.get_count()

print("joystick_count")

print(joystick_count)

print("--------------")

numaxes = joystick.get_numaxes()

print("numaxes")

print(numaxes)

print("--------------")

numbuttons = joystick.get_numbuttons()

print("numbuttons")

print(numbuttons)

print("--------------")

loopQuit = False

while loopQuit == False:

    # test joystick axes and prints values

    outstr = ""

    for i in range(0,4):

        axis = joystick.get_axis(i)

        outstr = outstr + str(i) + ":" + str(axis) + "|"

        print(outstr)

    # test controller buttons

    outstr = ""

    for i in range(0,numbuttons):

           button = joystick.get_button(i)

           outstr = outstr + str(i) + ":" + str(button) + "|"

    print(outstr)

    for event in pygame.event.get():

       if event.type == QUIT:

           loopQuit = True

       elif event.type == pygame.KEYDOWN:

           if event.key == pygame.K_ESCAPE:

               loopQuit = True

             

       # Returns Joystick Button Motion

       if event.type == pygame.JOYBUTTONDOWN:

        print("joy button down")

       if event.type == pygame.JOYBUTTONUP:

        print("joy button up")

       if event.type == pygame.JOYBALLMOTION:

        print("joy ball motion")

       # axis motion is movement of controller

       # dominates events when used

       if event.type == pygame.JOYAXISMOTION:

           # print("joy axis motion")

    time.sleep(0.01)

pygame.quit()

sys.exit()

When running this testing code, I would test each part of the remote separately so detecting the inputs is easier. For example to test the axis, I would comment out everything from '#test controller buttons' to '#print ("joy axis motion")' and run the program.

Building the program

I will require multiple commands to happen at the same time but only one command will be sent to the Robot Arm at once. Therefore, the python file will need to build the command, detecting a range of inputs and compile one output command. To build one command, the commands need to be combined from their binary format into one integer command (See ‘Basic Commands using a USB Robotic Arm with a Raspberry Pi’)

Here is the final program, ps3controller.py with explanations on each line.

import pygame #Import Modules

import usb.core

import time

pygame.init()#Initialize pygame

# Wait for a joystick

while pygame.joystick.get_count() == 0:

  print 'waiting for joystick count = %i' % pygame.joystick.get_count()

  time.sleep(10)

  pygame.joystick.quit()

  pygame.joystick.init()

j = pygame.joystick.Joystick(0)

j.init()#Initialize Joystick

print 'Initialized Joystick : %s' % j.get_name()#Print joystick if present

armFound = False

while not armFound: #Find Robot Arm

  dev = usb.core.find(idVendor=0x1267, idProduct=0x0000)

  if dev is None:#If Robot Arm not found, alert user

    print 'Arm not found. Waiting'

    time.sleep(10)

  else:

    armFound = True

#this arm should just have one configuration

dev.set_configuration()

#Print Controls to user

print("")

print("Joysticks:")

print("LEFT JOY UP/DOWN:    SHOULDER UP/DOWN")

print("LEFT JOY LEFT/RIGHT: BASE CLOCKWISE/ANTICLOCKWISE")

print("RIGHT JOY UP/DOWN:   ELBOW UP/DOWN")

print("R1: WRIST UP")

print("R2: WRIST DOWN")

print("X:  GRIP OPEN")

print("O:  GRIP CLOSE")

print("SELECT: TOGGLE LIGHT ON/OFF")

print("")

print("To Close, press 'Ctrl + C'")

# How far to move the JoyStick before it has an effect (0.60 = 60%)

threshold = 0.50#Sensitivity

# Key mappings

PS3_BUTTON_SELECT = 0

PS3_AXIS_LEFT_HORIZONTAL = 0

PS3_AXIS_LEFT_VERTICAL = 1

PS3_AXIS_RIGHT_HORIZONTAL = 2

PS3_AXIS_RIGHT_VERTICAL = 3

PS3_AXIS_X = 17

PS3_AXIS_CIRCLE = 18

PS3_AXIS_R1 = 15

PS3_AXIS_R2 = 13

# Robot Arm  defaults

Command = (0,0,0)

lightonoff = 0

shoulder = 0

base = 0

elbow = 0

wristup = 0

wristdown = 0

grip_open = 0

grip_close = 0

grip_command = 0

wrist_command = 0

shoulder_command = 0

base_command = 0

elbow_command = 0

           

 # ARM control

def SetCommand(axis_val):#Returns number depending on axis value

    if axis_val > threshold:

        return 1

    elif axis_val < -threshold:

        return 2

    elif abs(axis_val) < threshold:

        return 0

def BuildCommand(shoulc,basec,elbowc,wristc,gripc,lightc):#Builds Command

    byte1 = shoulc + elbowc +  wristc + gripc#Combines instructions for byte1

    list1 = [str(shoulc), str(elbowc), str(wristc), str(gripc), str(basec), str(lightc)]#Compiles commands into 1 command

        

def ProcessArm(event):#Detects input and processes

      global Command, lightonoff, shoulder, base, elbow, wristup, wristdown, grip_open, grip_close, grip_command, wrist_command, shoulder_command, base_command, elbow_command

     

      if event.type == pygame.JOYBUTTONDOWN:

          if event.button == PS3_BUTTON_SELECT:

            if lightonoff == 0:

              lightonoff = 1

            else:

              lightonoff = 0

      elif event.type == pygame.JOYAXISMOTION:

        if event.axis == PS3_AXIS_LEFT_VERTICAL:

          shoulder = event.value

        elif event.axis == PS3_AXIS_LEFT_HORIZONTAL:

          base = event.value

        elif event.axis == PS3_AXIS_RIGHT_VERTICAL:         

          elbow = event.value

        elif event.axis == PS3_AXIS_R1:   

          wristup = event.value

        elif event.axis == PS3_AXIS_R2:

          wristdown = event.value

        elif event.axis == PS3_AXIS_X:         

          grip_open = event.value

        elif event.axis == PS3_AXIS_CIRCLE:         

          grip_close = event.value

        # Open/Close Gripper?

        if grip_open > threshold:

            grip_command = 1

        elif grip_close > threshold:

            grip_command = 2

        else:

            grip_command = 0

       

       

        # Wrist Up/Down?

        if wristup > threshold:

            wrist_command = 1*4

        elif wristdown > threshold:

            wrist_command = 2*4

        else:

            wrist_command = 0

        #Produces final command for each 'body' part

        shoulder_command = SetCommand(shoulder)*64

        base_command = SetCommand(base)

        elbow_command = SetCommand(elbow)*16

       

        # Work out what to send out to the robot

        NewCommand = BuildCommand(shoulder_command,base_command,

                                  elbow_command, wrist_command, grip_command,lightonoff)

                                 

        # If the command has changed, send out the new one

        if NewCommand != Command:

            dev.ctrl_transfer(0x40, 6, 0x100, 0, NewCommand, 1000)

            Command = NewCommand

try:

    # Loop forever

    while True:

        time.sleep(0.1)#time.sleep(0.1)

       

        # read in events

        events = pygame.event.get()

              

        # and process them

        for event in events:

            ProcessArm(event)

except KeyboardInterrupt:

    j.quit()#End joystick input

For more information on the project above, go to:

https://www.pygame.org/docs/ref/joystick.html

https://theraspberryblonde.wordpress.com/2016/06/29/ps3-joystick-control-with-pygame/

Acknowledgements
Hiren's time was funded through Nuffield Foundation's Research Placement Scheme. The robot arm is part of Santander UK funding for Robots in Schools.

All opinions in this blog are the Author's and should not in any way be seen as reflecting the views of any organisation the Author has any association with. Twitter @scottturneruon

kitronik :Move mini buggy (Python control of LEDs)

In two previous posts I looked at control the :Move buggy using JavaScript Blocks or Python. In this post we are going to look at controlling the LEDs using Python (or more accurately micropython).

Pin 0 controls the LEDs, they are based on5  NeoPixel compatible, RGB, addressable LEDs; so the Neopixel protocols (and library for Neopixels) can be used. 

Code First five colours of the rainbow. The array lig holds the RGB settings for the rainbow colours (more details on the RGB colours can be found at Lorraine Underwood's Halloween Cloud project). In the code below, the five LEDs have a different colour allocated to them.

from microbit import *
import neopixel

np = neopixel.NeoPixel(pin0, 5)
lig=[[255,0,0],[255,127,0],[255,255,0],[0,255,0],[0,0,255],[75,0,136],[139,0,255]]
while True:
    np[0] = lig[0]
    np[1] = lig[1]
    np[2] = lig[2]
    np[3] = lig[3]
    np[4] = lig[4]

    np.show()


Code to cycle through the rainbow
from microbit import *
import neopixel

np = neopixel.NeoPixel(pin0, 5)
lig=[[255,0,0],[255,127,0],[255,255,0],[0,255,0],[0,0,255],[75,0,136],[139,0,255]]
count1=1
count0=0
count2=2
count3=3
count4=4
while True:
        np[0] = lig[count0]
        if count0>=6:
            count0=0;
        else:
            count0=count0+1
        np[1] = lig[count1]
        if count1>=6:
            count1=0;
        else:
            count1=count1+1
        np[2] = lig[count2]
        if count2>=6:
            count2=0;
        else:
            count2=count2+1
        np[3] = lig[count3]
        if count3>=6:
            count3=0;
        else:
            count3=count3+1
        np[4] = lig[count4]
        if count4>=6:
            count4=0;
        else:
            count4=count4+1
        np.show()

        sleep(500)


All opinions in this blog are the Author's and should not in any way be seen as reflecting the views of any organisation the Author has any association with. Twitter @scottturneruon

kitronik :Move buggy (Python controlled servos)

In a previous post I looked at controlling the Kitronik :Move buggy using Javascript based blocks. In this short post I will show controlling the servos of the micro:bit based :Move buggy with Python.

Control is via pin1(left motor) and pin2 (right motor) and the motors have to be driven in opposite directions to move forward or backwards. The direction of the motors is controlled by the analogue value written to the pins; pinX.write_analog(180) - anticlockwise or pinX.write_analog(1) - clockwise (pinX.write_analog(0) - stops the motor). Setting the analog_period seems to work at 20ms; this was found by experiment, discussed in a previous post.

So the initial code below sets up the moves for forward, backward, turn left, turn right all controlled with a move for so many milliseconds.

Code 
from microbit import *

pin1.set_analog_period(20)
pin2.set_analog_period(20)

def forward(N):
    pin1.write_analog(180)
    pin2.write_analog(1)
    sleep(N)
    
def backward(N):
    pin1.write_analog(1)
    pin2.write_analog(180)
    sleep(N)

def turnLeft(N):
    pin1.write_analog(1)
    pin2.write_analog(1)
    sleep(N)

def turnRight(N):
    pin1.write_analog(180)
    pin2.write_analog(180)
    sleep(N)

while True:
    forward(1500)
    backward(1500)
    turnLeft(1500)
    turnRight(1500)   

I would recommend running the :Move buggy on a surface that isn't smooth, I found the wheels slipping on a smooth surface. This is a really nice little robot to play with.

All opinions in this blog are the Author's and should not in any way be seen as reflecting the views of any organisation the Author has any association with. Twitter @scottturneruon

kitronik :Move mini buggy (JavaScript blocks)

Finally got around to building add playing with the Kitronik :Move https://www.kitronik.co.uk/5624-move-mini-buggy-kit-excl-microbit.html (see below - I decided to put the green sides on the outside - just to be different). One of its features is a vertical set of holes for a pen to be placed in.

Add the blocks (found at https://github.com/KitronikLtd/pxt-kitronik-servo-lite) in blocks editor (https://makecode.microbit.org/) to control the motors. You can do the same thing with writing to the pins, those instructions come with the build instructions, but using the extra blocks  is a little easier to understand. Also add the package for neopixels (type in neopixels in the search box to find them). Two very good tutorials I found useful to start with can be found at:

• Neopixels on the robot  in blocks - https://www.kitronik.co.uk/blog/using-kitronik-zip-leds-bbc-microbit/
• Servos on the robot in blocks - https://www.kitronik.co.uk/blog/kitronik-custom-pxt-editor-servo-blocks/

1. Motor example
I wanted it so that press A on the Micro:bit the robot goes turns right, goes forward, goes back and turns left. 

A stop block does need to be included, without it the :Move will continue moving. The wheels I found can slip on some surfaces reducing the precision, but still fun to play with.

2. At the start and stopping.
I want to use the motors and the 'pixels', but I want to have a known starting position for the motors and set the turning speed; this was possible using the blocks (see below). The pixels are set at this point on pin P0 (see below) as well. 

To stop both the motors and cycling of the pixels - pressing buttons A+B together was set up to this.

3. Rainbow on the pixels.

On pressing button B the pixels rotate through a range of colours.

4. Summary
This is great fun. Having the set of blocks adding for the servos means it is a bit simpler to work with. 

All opinions in this blog are the Author's and should not in any way be seen as reflecting the views of any organisation the Author has any association with. Twitter @scottturneruon

genetic algorithms to select filters for evoked potential enhancement

Use of evolutionary algorithms to select filters for evoked potential enhancement

Scott Turner

University of Leicester

Published: 2000

http://hdl.handle.net/2381/29366
DOI: 10.13140/RG.2.1.3654.3204

Abstract
Evoked potentials are electrical signals produced by the nervous system in response to a stimulus. In general these signals are noisy with a low signal to noise ratio. The aim was to investigate ways of extracting the evoked response within an evoked potential recording, achieving a similar signal to noise ratio as conventional averaging but with less repetitions per average. In this thesis, evolutionary algorithms were used in three ways to extract the evoked potentials from a noisy background. First, evolutionary algorithms selected the cut-off frequencies for a set of filters. A different filter or filter bank was produced for each data set. The noisy signal was passed through each filter in a bank of filters the filter bank output was a weighted sum of the individual filter outputs. The goal was to use three filters ideally one for each of the three regions (early, middle and late components), but the use of five filters was also investigated. Each signal was split into two time domains: the first 30ms of the signal and the region 30 to 400ms. Filter banks were then developed for these regions separately. Secondly, instead of using a single set of filters applied to the whole signal, different filters (or combinations of filters) were applied at different times. Evolutionary algorithms are used to select the duration of each filter, as well as the frequency parameters and weightings of the filters. Three filtering approaches were investigated. Finally, wavelets in conjunction with an evolutionary algorithm were used to select particular wavelets and wavelet parameters. A comparison of these methods with optimal filtering methods and averaging was made. Averages of 10 signals were found suitable, and time-varying techniques were found to perform better than applying one filter to the whole signal.

Full text versions are available from:

• https://lra.le.ac.uk/handle/2381/29366
• https://www.researchgate.net/publication/235424726_Use_of_evolutionary_algorithms_to_select_filters_for_evoked_potential_enhancement

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Cozmo, Ohbot go to Code Club

I have recently taken two robots to a Code Club, here are a couple of reflections/observations.


Cozmo
This robot produced by Anki is incredibly cute - a cross between Wall-E and a pet in some respects.

The code below was produced by the 'Code-Clubbers' and gets Cozmo to speak move around and operate its forks at the front. Anecdotally, someone was trying to work on something but couldn't resist coming and having another look at what it was doing.

Ohbot

Ohbot provided a different opportunity to play with a robot, getting to move the mouth, speak and track faces. My first impression was some of the children were a bit wary, until they found out they could control what it says and that seemed to break the ice.





All opinions in this blog are the Author's and should not in any way be seen as reflecting the views of any organisation the Author has any association with. Twitter @scottturneruon