Lego EV3

This library leverages the ev3dev.org project to provide a dead simple way to program the Lego Mindstorms EV3 starter kit in Ruby.

Getting started

gem install lego_ev3

Then:

mkdir example
touch example/script.rb
touch example/config.yml

Put in script.rb:

require 'lego_ev3'

connection = LegoEv3::Connection.new

brick = LegoEv3::Brick.new(connection)

# Plug any sensor in any input.
s = brick.sensors.first

100.times do
  puts s.poll
end

connection.close

Put in config.yml:

entry_point: script.rb
remote:
  host: '192.168.2.3'
  hostname: 'ev3dev'
  username: 'root'
  password: 'r00tme'
  ssh: 22
  tcp: 13603
  service: 'ssh'

Execute the script with:

lego-ev3 example -R

This will open an SSH connection to the brick to send commands. This is one way of doing things, read below for more options.

Setup the brick to use Ruby

Make sure you have the necessary dependencies

The ev3dev.org distribution contains Ruby 2 but some libraries are missing to build native extensions. Running local scripts with this lib requires native extensions to work.

Solution #1: Use RVM.

Solution #2: Install those dependencies:

apt-get install build-essential bison openssl libreadline6 libreadline6-dev curl git-core zlib1g zlib1g-dev libssl-dev libyaml-dev libxml2-dev autoconf libc6-dev ncurses-dev automake libtool ruby-dev

(Optional) Faster gem install operations

To install gems faster, make sure your ~/.gemrc on the brick looks like:

---
:verbose: true
:sources:
- http://rubygems.org/
:update_sources: true
:backtrace: false
:bulk_threshold: 1000
:benchmark: false
gem: --no-ri --no-rdoc --verbose

Running a script remotely on the brick for debugging

This is the mode used in Getting started above. This mode requires remote.service: 'ssh' in the config.

• [+] No need to setup the brick to use Ruby
• [+] No need to send files to the brick
• [+] Can use breakpoints in script using Pry
• [-] The slowest approach (~200 ms per command)

Execute the script with:

lego-ev3 example -R

Running a script locally on the brick

The same script in Getting started above can be ran locally on the brick without modifying the code.

• [-] Need to setup the brick to use Ruby
• [-] Need to send files to the brick
• [-] Cannot use breakpoints in script
• [+] Fastest approach (~0.7 ms per command)

Sending a script to the brick:

lego-ev3 example -u -r

This will:

• Upload the script to the brick (-u) at /home/example.
• Execute ruby /home/example/script.rb through an SSH connection and capture the output.

How can the same code be used remotely and locally?

The LegoEv3::Connection class is smart enough to determine if the script being executed is on your machine or directly on the brick. To accomplish this, this class uses the hostname parameter in the config.

Running a script remotely on the brick for a test run

• [-] Need to setup the brick to use Ruby
• [+] No need to send files to the brick
• [+] Can use breakpoints in script using Pry
• [+] Slow approach (~40 ms per command)

This mode requires remote.service: 'tcp' in the config.

lego-ev3 example -s # Spawn the TCP server on the brick
lego-ev3 example -R # Execute the script with a TCP client

Note that the TCP server is spawned in background on the brick. To spawn it in foreground, you need to connect to the brick.

TODO

• Add a DSL on top of current lib
• Add a state machine on top of current lib
• Use the state machine to produce graphs of robot logic
• Add logging and easy way to produce sensor graphs
• Polling sensors should probably be multi-threaded
• Add examples