Published September 6, 2019 © CC BY-NC-SA

Mooomba - The Cow Roomba

Always wanted a cow, but don't have the space? Build yourself this Roomba-sized cow!

IntermediateFull instructions providedOver 1 day2,118

Things used in this project

Hardware components

Raspberry Pi 3 Model B

Seeed Studio Grove - 2-Channel SPDT Relay

Battery Holder, AA x 8

Powerbank 5v 2.1A

Adafruit Mini External USB Stereo Speaker

Wheels

DC Motor - 37mm - 12V - 50RPM

Swivel Wheel

Cow

Fake grass

Wooden Platform

Software apps and online services

Raspberry Pi Raspbian

Hand tools and fabrication machines

Hot glue gun (generic)

3D Printer (generic)

Paint

Multitool, Screwdriver

Scissors, Free Fall

Story

Overview

Below a quick overview of the content.

Introduction and showcase video
Movement
Control
Sound
Style
Adventure

Introduction and showcase video

My girlfriend really wants a cow. Sadly, that's a bit tricky because we live in an apartment. I did however find a small inflatable version in the local thrift store. This means we can make her a robot cow for adventuring, The Mooomba!

Project Video

Movement

A cow can move around, so our Mooomba needs some wheels and power to match. Two DC motors in the front and a small swivel wheel in de back will do perfectly!

Baseplate with motors and wheel

To attach the motor we drill two holes on each side, and using the motor bracket, screw them both in place.

Motor #1

Here's a dirty bit, the wheels I'm using don't really fit on the motor shaft. To fix this we're going to us some hot glue, I know....

Sinning

We can attach the swivel wheel in exactly the same way.

Screwing in the swivel

With our motors, wheels and swivel in place we can test if it has enough oempf to move around our pint-sized cow.All we need to do is attach the motor wires to a 12v power source and see what happens.

It works!

Our miniature herbivore can move, woopwoop!It's still manually controlled though, let's change that by mo(o)ving on to the next part.

Control

To make our lives easier and give the Mooomba a sense of self, we're going to add some electronics.

Electronics

The Raspberry Pi is powered by a 5v powerbank (black block on the left).This Pi controls a two channel relay (black/blue thing on the right). The relay on its turn will open/close the connections between the 12v battery pack and the two motors. This means;

Both relays open => no power => no movement
Both relays closed => both motors powered => forward
One relay closed => one motor powered => left or right

We want to make a high quality cow, so we 3D print some braces to keep everything in place. The files for these braces are attached to this article.

All that is left to do is write some code. You can find the full code in the section "Code", but here's a overview of how it works.
Generate a number between 0 and 3 and do the following;
0 => Forward
1 => Turn right
2 => Turn left
3 => Play audio (see next section)

This is repeated until eternity, or the batteries run out.

Sound

Every cow can make sound, so ours will too!The first thing we need is a volunteer to do their best cow impression on camera.

Cow impression

We take this audio and save it as mp3, adding a USB speaker makes sure everyone can hear Mooombas majestic calls.

USB Speaker

Style

Last but not least, some style. To really bring out the best we add some fake grass to our moving platform, give Mooomba a good wash and add the all important cowbell. Doesn't she look fab?

Looking good!

Adventure

MOOOOOOO

Now you're all ready to go adventuring with your mini cow! Just don't forget to stop and smell the flowers. :-)

Code

Code

import RPi.GPIO as GPIO  
import time  
import random
import os

GPIO.cleanup()
GPIO.setmode(GPIO.BCM)  

left = 20
right = 21
GPIO.setup(left, GPIO.OUT) 
GPIO.setup(right, GPIO.OUT) 



def turnLeft():

    print("Left!")
    GPIO.output(left, GPIO.LOW)  
    time.sleep(2)
    GPIO.output(left, GPIO.HIGH)


def turnRight():
    print("Right!")
    GPIO.output(right, GPIO.LOW)  
    time.sleep(2)
    GPIO.output(right, GPIO.HIGH)

def forward():

    print("Forward!")
    GPIO.output(left, GPIO.LOW)  
    GPIO.output(right, GPIO.LOW)

    time.sleep(2)  

    GPIO.output(left, GPIO.HIGH)  
    GPIO.output(right, GPIO.HIGH)  

def playAudio():
    # Collect all the names of the images in out folder and the amount
    names = [name for name in os.listdir('/home/pi/Desktop/moomba/audio')]
    total = len([name for name in os.listdir('/home/pi/Desktop/moomba/audio')])

    # Generate a random number, -1 because our index start at 0
    randomInt = random.randint(0, total-1)
    print(total)

    # Fetch the name belonging to this random number
    name = '/home/pi/Desktop/moomba/audio/'+names[randomInt]
    print(name)

    #Play the audio
    os.system('mpg123 ' + name)
    time.sleep(0.2)

def turnOff():
    print('Off')
    GPIO.output(left, GPIO.HIGH)  
    GPIO.output(right, GPIO.HIGH)  

while True:

    actionInt = random.randint(0,3) 

    if actionInt == 0:
        forward()
    elif actionInt == 1:
        turnRight()
    elif actionInt == 2:
        turnLeft()
    elif actionInt == 3:
        playAudio()

    time.sleep(2)

Mooomba - The Cow Roomba

Things used in this project

Hardware components

Software apps and online services

Hand tools and fabrication machines

Story

Overview

Introduction and showcase video

Movement

Control

Sound

Style

Adventure

Custom parts and enclosures

Bracket

Code

Code

Credits

Comments

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Mooomba - The Cow Roomba

Mooomba - The Cow Roomba

Things used in this project

Hardware components

Software apps and online services

Hand tools and fabrication machines

Story

Overview

Introduction and showcase video

Movement

Control

Sound

Style

Adventure

Custom parts and enclosures

Bracket

Code

Code

Credits

Comments

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