Arduino Lego Robot – Update 1

I’ve been building  an Arduino powered Lego tracked robot on and off for the past half year, and have finally come to the point where there’s something to show.

I didn’t take long to realize that I had to become proficient in programming and not just patch together other people’s code from the web, so I took a crash course in Python (using the excellent book Python Crash Course by Eric Matthes) and became familiar with C and C++ for the Arduino code.

After a few months of coding I’m finally at the point where it is all coming together. I’ve had the basic Lego robot built for months but never really programmed it to do anything other than running forward and stopping. The robot is built of parts from the Lego Crawler Crane kit (#42042), it’s basically the tracked base with some modifications like a motor for each track to allow steering. The motors are controlled via the Arduino (see my first blog entry), which in turn is controlled with a Python program on my PC via the serial monitor. The plan is to have a Raspberry Pi as the onboard PC, which in turn will be controlled via Wifi from another PC or laptop.

Back view of the robot

Top View

At the moment the robot is controlled with a simple Python program using the WASD keyboard keys, allowing forward and backward movement and turning. This works relatively well, with about a 1 second delay.

I took the video below when testing the serial communications; at that point I had only programmed forward movement.

I have attached the Arduino code below. It waits for a serial command to actuate the motors. If you intend to use this code yourself, be aware that some lines may be split because of the narrow WordPress theme format (should be fixed by now).

// Tank movement controlled via serial commands
// Works with Adafruit Motor Shield v.2.3
// Written by Kenneth Larsen, 2017

#include <Wire.h>
#include <Adafruit_MotorShield.h>
#include "utility/Adafruit_MS_PWMServoDriver.h"

// Create the motor shield object with the default I2C address
Adafruit_MotorShield AFMS = Adafruit_MotorShield();

// Select ports for motors: M1 - M4. 
Adafruit_DCMotor *Motor1 = AFMS.getMotor(1);
Adafruit_DCMotor *Motor2 = AFMS.getMotor(2);

String input; // input for Serial
int c = -20; // error correction
int FULLSPEED = 255;
int HALFSPEED = 126;

void setup()
 {
 Serial.begin(115200);
 AFMS.begin(); // create with the default frequency of 1,6KHz
 }

void moveForward()
// Define forward movement
{
 Serial.println("Moving forward...");
 uint8_t i;
 Motor1->run(FORWARD);
 Motor2->run(FORWARD);
 for ( i = 30 ; i < 255 ; i++ ) // accelerate slowly
 {
 Motor1->setSpeed(i);
 Motor2->setSpeed(i+c); 
 delay(10);
 }
 Motor1->setSpeed(FULLSPEED); // maintain max speed
 Motor2->setSpeed(FULLSPEED+c);
}

void moveBackward()
// Define backward movement
{
 Serial.println("Moving backward...");
 uint8_t i;
 Motor1->run(BACKWARD);
 Motor2->run(BACKWARD);
 for ( i = 30 ; i < 255 ; i++ ) // accelerate slowly
 {
 Motor1->setSpeed(i);
 Motor2->setSpeed(i+c); 
 delay(10);
 }
 Motor1->setSpeed(FULLSPEED); // maintain max speed
 Motor2->setSpeed(FULLSPEED+c);
}

void turnLeft()
// Define left turns
{
 Serial.println("Turning left...");
 Motor1->run(BACKWARD);
 Motor2->run(FORWARD);
 Motor1->setSpeed(HALFSPEED);
 Motor2->setSpeed(HALFSPEED);
}

void turnRight()
// Define right turns
{
 Serial.println("Turning right...");
 Motor1->run(FORWARD);
 Motor2->run(BACKWARD);
 Motor1->setSpeed(HALFSPEED);
 Motor2->setSpeed(HALFSPEED);
}

void stopMovement()
// Define stopping
{
 Serial.println("Stopping...");
 Motor1->run(RELEASE); // stop motors
 Motor2->run(RELEASE);
}

void loop()
{
 if (Serial.available() > 0)
 {
 input = Serial.readString();
 if (input == "forward")
 {
 moveForward();
 }
 if (input == "backward")
 {
 moveBackward();
 }
 if (input == "left")
 {
 turnLeft();
 }
 if (input == "right")
 {
 turnRight();
 }
 if (input == "stop")
 {
 stopMovement();
 }
 }
}

The Python code uses pygame to grab the keystrokes and send them to the Arduino via serial. I’ll split this program into two, one for the PC to send the commands and receive video, and another for the Raspberry Pi to forward the commands to the Arduino and send video directly from the Raspicam to the PC. This will be done over WiFi to make the robot completely cordless, and with better range than if I went with Bluetooth (and better security!).

# Serial control for Arduino robot
# Written by Kenneth Larsen, 2017
import serial, sys
import pygame

# Initialize pygame
pygame.init()
pygame.display.set_caption("Robot Control Center")
screen = pygame.display.set_mode((640,480))

# Initialize serial connection
try:
 ser = serial.Serial('/dev/ttyACM1', 115200)
except serial.serialutil.SerialException:
 try:
 ser = serial.Serial('/dev/ttyACM0', 115200)
 except serial.serialutil.SerialException:
 print("No serial connection found. Is the Arduino connected?\n")

# Define stop keys. Releasing any of these keys will cause the robot to stop
stopkeys = (pygame.K_w, pygame.K_a, pygame.K_s, pygame.K_d)

def quitprogram():
 """Handles program shut down."""
 print("Stopping robot and exiting...\n")
 # Stop motors
 ser.write(b'stop')
 sys.exit()

# Main loop
while True:
 screen.fill((255,255,255))
 for event in pygame.event.get():
 if event.type == pygame.QUIT:
 quitprogram()
 # Keyboard controls
 if event.type == pygame.KEYDOWN:
 if event.key == pygame.K_q:
 quitprogram()
 if event.key == pygame.K_w:
 ser.write(b'forward')
 print(ser.readline().decode('UTF-8'))
 if event.key == pygame.K_s:
 ser.write(b'backward')
 print(ser.readline().decode('UTF-8'))
 if event.key == pygame.K_a:
 ser.write(b'left')
 print(ser.readline().decode('UTF-8'))
 elif event.key == pygame.K_d:
 ser.write(b'right')
 print(ser.readline().decode('UTF-8'))
 elif event.type == pygame.KEYUP:
 if event.key in stopkeys:
 #if event.key == pygame.K_w or pygame.K_s or pygame.K_a or pygame.K_d:
 ser.write(b'stop')
 print(ser.readline().decode('UTF-8'))
 
 # Update display
 pygame.display.update()

This is just the initial programming of the robot. I’ve tried to keep everything as simple as possible to assure that it all works.

Next step will be to get the Raspberry Pi on the robot and connect the Arduino directly to it. I’m currently experimenting with sending live video from the Raspberry over Python. The next update will hopefully focus on this, with the robot controlled over WiFi from a laptop.

Part 2 is now available!

Running Linux on the Asus C201PA Chromebook

I was recently looking for a cheap laptop to run Linux on, mostly for programming. I settled on the Asus C201PA Chromebook for two reasons: I have good experience with Asus Hardware, and there were many success stories of people running Linux on it.

Kali Linux have an image available for the Chromebook Flip, which is almost identical to the C201PA. Installation is really straightforward, but I’m going to detail how I did it here since I ran into a few issues.

First, put the Chromebook into Developer Mode (warning: this will erase all personal data in ChromeOS). This lets you boot other operating systems. To do this, hold down ESC + REFRESH (F3) and touch the Power button. When the Chromebook reboots, select Recovery, then press CTRL + D. This boots ChromeOS in Developer Mode.

Once booted, press CTRL + ALT + T to open the terminal. Write

shell

to get the shell, then

sudo su

to get root. In order to boot Linux from a microSD or USB drive, run the command

crossystem dev_boot_usb=1

which enables USB booting.

Now you need to prepare the MicroSD (or USB) drive with Kali Linux. Download the Kali Linux image to your computer (or Chromebook) and run

xzcat kali-$version-veyron.img.xz | dd of=/dev/sdx bs=512k

Substituting $version with the specific version you downloaded. /dev/sdx would be your MicroSD card or USB drive (be extra careful to get it right, as the dd command will erase your drive!).

This is where I started to run into a small issue: The Kali image is made for an 8 GiB drive, and I was using a 16 GiB. This meant 8 GiB completely unusable space on the drive. To solve this, you need to use parted and cgpt (cgpt is part of vboot-utils) to change the size of the root partition:

parted /dev/sdx
>print

Where /dev/sdx is once again your Kali drive. Parted will complain that not all the space appears to be used, and that it can fix it for you. Let it do so. Unfortunately, we are not done yet. If you try to boot Kali now, you will find that the drive is unbootable.

You’ll have to run

cgpt show /dev/sdx

And write down the number in the column Start at the row Sec GPT table. We need this number to calculate the size of the root partition for the next command:

cgpt add -i 2 -t data -b 40960 -s `expr X – 40960` -l Root /dev/sdx

where X is the number you just found. Careful, the “`” is the key to the left of the “1” (on UK keyboards).

Repair the partition layout using

cgpt repair /dev/sdx

Re-add the boot partitions by

cgpt add -i 1 -S 1 -T 5 -P 10 -l KERN-A /dev/sdx
cgpt add -i 2 -S 1 -T 5 -P 5 -l KERN-B /dev/sdx

And finally, expand the root filesystem by:

mount /dev/sdx2 /mnt/tmp

Assuming /mnt/tmp exits, and then

resize2fs /dev/sdx2

 

Finally, the microSD or USB drive is ready! Plug it into the Chromebook, power it on, and press CTRL + U at the white boot screen to boot from USB. Kali Linux should now boot and present you with the login screen. Username is root, password is toor.

You should change the root password with ‘passwd’, and if you decide to use Kali for everyday use, I’d recommend adding a new user with

useradd -m -s /bin/bash (username)
passwd (username)

And then install and use sudo for when you need elevated privileges.

 

Apart from Kali, it is also possible to install and run Arch Linux. I have it running on another microSD card, but have to solve some issues before I’m happy with it (probably related to the framebuffer).

I’ve also tried installing Gentoo Linux, and got as far as running it but was unable to get the network adaptors working. They need pre-compiled modules that I was not able to load. If I ever get it working, I’ll make a new blog post about it. Gentoo is what I’m running on my desktop and Raspberry Pi, and would prefer to run it on the Chromebook too.

I’m also debating whether to move Kali or Arch to the internal memory, wiping ChromeOS. I have still to make that decision, though.


Sources:

  1. https://www.chromium.org/a/chromium.org/dev/chromium-os/developer-information-for-chrome-os-devices/generic
  2. http://docs.kali.org/kali-on-arm/kali-linux-asus-chromebook-flip
  3. https://forums.kali.org/showthread.php?27350-Chromebook-expand-resize-grow-partition-rootfs

My Model Shipyard

For the past 15 years or so I’ve been building model sailing ships on and off. This has resulted in 2 finished kit models, one of them modified, and one scratch-built model still under construction.

I’ve had some pictures of my ship models on several websites, but what with the nature of the web, most of these sites no longer exist.  For that reason I’ve decided to leave a few pictures on this blog, with a brief description of the ships.

 

HM MORTAR VESSEL CONVULSION

This was the first kit model I finished, and while the subject is certainly not the most beautiful ship ever built, I was quite happy with the result. It’s a rather small ship and doesn’t have as many details as my later models.

HM Mortar Vessel Convulsion

Deck details

HM BOMB VESSEL GRANADO

Continuing my theme with bomb vessels, I then built the “Granado”, a British bomb vessel from 1756. This is also a kit model, but I have made several modifications such as the hand-carved stern gallery and figurehead.

HM Bomb Vessel Granado

Stern details – the gallery is hand-carved from Swiss pear.

Hermes decorating the stem – with a bomb in his right hand!

Rigging

Stern view

USS SYREN

The current ship I’m building – and have been building for the past 9 years or so – is the USS Syren, a 18-gun brig of the fledgling US Navy of 1803. This is a scratch-built model made from plans acquired at Model Ship World.  As can be seen from the photos, it is far from finished and will take several years more to finish, especially at my current tortuous pace…

USS Syren

Carronade details

Head rails

Progress as of writing

I’d like to say that my skills have progressed noticeably since my first ship; unfortunately, that has come at the cost of slower progress, especially since I have a large amount of other hobbies demanding my time.

 

In the future, I’ll detail some specific parts of the construction of the USS Syren, which may be of interest to other model ship builders.

If you have any questions or comments, please don’t hesitate to contact me (contact details in ‘about’ in the upper right corner)!

Audio Selector

I usually change a lot between speakers and headphones on my PC – Speakers when I watch movies or listen to music, and headphones when I’m at the desktop. I hate having to insert and remove the jack every time I want to change, so about a year ago I bought a cheap audio selector from Amazon. That worked for about half a year until one channel started to become lower volume than the other. So instead of just buying some new cheap selector, I decided to channel my inner maker and make my own.

I decided to go with 3 outputs so I could connect an extra pair of speakers in the future. I was able to get some 3-input 2-position switches at my local electronics store that I could just wire with 1 input and 1 output to get the desired off-on effect.

The circuit is rather simple: connect the centre of all the switches to the input jack (red wire right speaker (ring), white wire left speaker (tip), black ground (sleeve)), and one side of each switch to an output jack (the 3rd side will be empty, corresponding to OFF).

audio_selector_schem

Diagram shows only 2 switches, but can easily be expanded

Having taken some quick measurements (the box had to fit below my secondary monitor) I made a back-of-the-envelope draft of the design and collected the parts. For my design I needed 4 3,5mm female audio jacks, 2 male jacks (to connect the input side of the box to the PC), 3 switches and some cable.

Audio Selector - Pieces

I decided to go with American walnut for the box as I had several sheets lying around at varying thickness. I ended up using 4 mm thick sheets for the end pieces and 2 mm for the rest. The backside was problematic, the female audio jacks I had bought could only be screwed onto a plate of maximum 1 mm thickness, and walnut is rather brittle at that thickness. Eventually I found the lid of a plastic cookie box and used that for the back side. Cheap and easy!

Construction of the box was quick and straightforward:

Creating the box

Creating the box

Though soldering the switches and cables allowed me to practice some new swear words (I’ve never been good at soldering).

To finish the box I sanded it with some fine grit sandpaper and gave it a coat of linseed oil. In the future I might draw numbers or symbols over each switch on the front to identify it.

Audio Selector - Back

Viewed from the back. The red plate is from a cookie box.

Audio Selector - Front

Finished audio selector

All in all, this was a fun 2-day project for me. In total I think the parts cost me some 20€; I might have been able to get a finished box cheaper, though I’ve not had much luck finding any for sale, and the few on Amazon are either very expensive or poor quality.  I’m very happy with the result, the switches are nice to operate and the box is sturdy and looks good on my desk. And most importantly, you just can’t beat home-made electronics!

Arduino & Lego PF Motors

Working through the book Arduino Workshop by John Boxall I’ve finally come to the chapter describing how to build an Arduino Tank Robot. However, instead of buying a premade robot chassis I decided to make it out of Lego Technic instead, something I played a lot with as a child.

This presented me with some interesting challenges, first of all, how to interface the Lego Power Functions motors with the Arduino. Luckily, I’m not the first one doing this stuff, and I quickly found a great blog detailing how to cut the motor cables. As I didn’t want to permanently destroy the great Lego set I had just bought (the 42042 Crawler Crane), I bought some new cables and an extra motor from Lego.

Preparing the cables was easy: cut them, strip and tin the two outer wires for the battery pack (+9V and GND), and the two inner cables for the motors.

Jpeg

Cutting the cables (Lego fans should look away!)

To check if it all worked, I built a quick circuit with a TIP122 transistor according to this Arduino tutorial (though a bit simplified, I didn’t really need the switch). It worked perfectly, and I was able to control the motor speed with some simple PWM code. Next step was to run 2 motors off the Adafruit motor shield. As you can see in the video below, it all worked perfectly.

Jump on over to the first entry of how I built and programmed my Arduino Lego Robot: Arduino Lego Robot – Entry 1.

Jpeg

Arduino Lego Tank Robot