A survey of robotics in Ruby

A Survey of Robotics
in Ruby
Josh Adams | @knewter
Adam Dill | @adamdill
Saturday, June 15, 13
A
This is Josh Adam from Isotope 11
I am Adam DIll from Inside.com
And how can it not be fun, were talking about robots!

This talk has two parts
• Survey / knowledge dump
• Project narrative
J:
This talk has a couple of parts. The ﬁrst one is really just a braindump - lots of good information on the library landscape.
After that, we’ll dig into building a project together

Part the first
A Survey of Robotics with Ruby
A
So lets dive into the survey so you guys can see what is out there

Robots?
• A machine capable of carrying out a complex series of actions
automatically.
• (esp. in science fiction) A machine resembling a human being
and able to replicate certain human movements and
functions.
• Robotics: The branch of technology that deals with the
design, construction, operation, and application of robots.
A:
What is a robot?
a robot is a force multiplier, it lets you take a simple action and cause a cascade of more complex decisions and actions
JOSH

Robots?
• A machine capable of carrying out a complex series of actions
automatically.
• (esp. in science fiction) A machine resembling a human being
and able to replicate certain human movements and
functions.
• Robotics: The branch of technology that deals with the
design, construction, operation, and application of robots.
LAM
ESaturday, June 15, 13

ROBOTS!!!1!!!one!
http://www.ﬂickr.com/photos/torek/3788181603/
J
We all know what robots are, right? They’re awesome

State of Hobby Robotics
• Growing rapidly
• lots of good mags
• My 3 favorites =>
• Costs have fallen
• Getting really approachable
A
mass production of sensors for phones has made this affordable
while the maker movement has made this approachable approachable
great references are available, make ﬁrst among them

State of Hobby Robotics
with Ruby
• http://artoo.io/ - Sinatra for Robots
• https://github.com/hparra/ruby-serialport/
• http://www.rock-robotics.org - heavily c based, wired
together with Ruby
• right now, Python is better, and certainly more active, and
more mature
• long term, Ruby is a great choice
A
Artoo is like sinatra for Robotics. It’s deﬁnitely leading the pack right now.
Serialport is an easy way to use serial devices, but there are some baud rate issues.
Rock robotics is mostly C-based, but wired together with Ruby
Python’s presently outpacing us in robots, but Ruby is the future.
J
Why is Ruby such a good choice, Adam?

Why is Ruby a great choice?
• All the normal reasons Ruby is great
• DSLs
• Metaprogramming
• Developer happiness
A
All the normal reasons:
DSLs, Metaprogramming, and you can have fun *writing* your robots, not just playing with them.

Artoo.io Example
J
So we aren’t going to dig into artoo too much, but it’s deﬁnitely worth checking out.
Artoo’s awesome and provides a common interface for various
devices. It’s really made for controlling toys, which is fun and
an easy way to start.
It also gives you an easy way to roll a web API interface for your system.
(It also uses Celluloid, which is easily my favorite Ruby library)

Where to start?
• Get easy wins early:
• Sphero - about $130
• Parrot ARDrone - about $150 refurb
A
Don’t start with a giant project
It’s very easy to get bogged down in a small hardware problem (resistor values, etc)
J
When should I learn Ohm’s Law, etc?
A
Right. So make sure to get some easy wins up front to help keep yourself motivated.
I suggest you buy either a sphero or a Parrot ARDrone and just play with it.

Sphero
• http://www.gosphero.com/
• Bluetooth enabled ball
• drives itself around
• best dog toy ever
• waterproof
A
This is a sphero. It’s basically just a ball with a motor inside of it.
It’s bluetooth-controlled (via serialport), it’s a lot of fun and really simple.
These are great for someone just learning to program to see real-world results of the code they’re typing, so it’d be good for
teaching kids and keeping them engaged.
There are some great KidsRuby Artoo resources for the Sphero

Sphero with Ruby
A
Cool Sphero gems, and artoo supports it.
You can see we’re just giving it a speed and a direction. It doesn’t get much simpler than this.
(DEMO)

A
Here’s an example of using Artoo to control an armada (ﬂeet?) of spheros
What’s cool here is you can see how multitasking works with this evented architecture.

Parrot ARDrone
• http://ardrone2.parrot.com/
• Acts as its own wifi AP
• Connect to it over wifi, it’s
just a device with an IP
• Send UDP packets to it
• Stream video from 2
cameras
J
So the other easy toy is the Parrot ARDrone. This guy creates his own WiFi access point that you connect to, then you can just
send him UDP packets to control him. He’s also got a couple of video cameras.
Like we said, it’s $150 for a refurb and you can get a new one for around $250

Parrot ARDrone
J
Jim Weirich wrote the `argus` gem to control it via Ruby
Artoo supports it
(DEMO)

Rolling your own
• What if you don’t want a ball or a quadcopter? What if you
want to be master of your own fate?
J
So now you’ve got your easy wins and you’re still interested. What’s next?

Microcontrollers
A microcontroller is a small computer on
a single IC containing a processor,
memory, and programmable I/O. -
wikipedia
A
Microcontrollers are essentially tiny computers. The real keys are they are on a single board, and have I/O.

Microcontrollers!!!!!11!!!
wtfbbqhax
J
The arduino showed up right around the same time Make magazine did, and they had a huge impact on hobbyists (though people
that were doing microcontrollers before that will hate me for saying that). Still, it’s only a 16MHz device with virtually no storage,
no networking, and it had to be programmed in C. Now we have a whole range of options, from the Beaglebone Black to the
PCDuino, which offers a 1GHz chip, 1GB of RAM, a Mali 400 GPU, and an Arduino-compatible pinout (so you can take advantage
of existing shields). Those are both far more expensive and power hungry than the almighty Raspberry Pi, though. With a RasPi,
you get 700MHz, 512MB RAM, and networking for $35, as well as lots of GPIO to hook into. It just really hits a sweet spot.

wtfbbqhax
Arduino
J

wtfbbqhax
Beaglebone
Black
Arduino
J

wtfbbqhax
Beaglebone
Black
Arduino
PCDuino
J

wtfbbqhax
Beaglebone
Black
Arduino
PCDuino
Raspberry Pi
J

Raspberry Pi
The Raspberry Pi is a credit-
card sized computer that plugs
into your TV and a keyboard.
It’s a capable little PC which
can be used for many of the
things that your desktop PC
does, like spreadsheets, word-
processing and games. It also
plays high-definition video.
A
Josh will go ahead and pass around the Pi
[run through ports]

RaspberryPi Setup
• dd image to memory card
• plug it all up (power last)
• about a dozen setup questions
• Debian LXDE setup (lightweight x11)
• can also run Arch
• straight console if that's all you want
A
setup is really easy, dd takes about 30 min, but other than that your running in under 15 min

RaspberryPi:
Running Ruby
• install RVM normally
• install ruby via rvm
• takes a long time to compile
• 1.9.3 seems to work better, mostly due to compile times and
gem compatibility
• expect this to change in the coming months
((Josh setup RC car))
A
Getting ruby running is about as easy, I used RVM, compile takes a few hours
1.9.3 seems to be the best right now, I expect this will change soon

RaspberryPi GPIO and Tips
• be careful with the Pi, need buffering, grab some transistors
or a ULN2003 to protect it.
• limited hardware PWM out of the box (1, shared with audio).
We’ll get you around that limitation a little later.
• You need at least a 1-amp power supply, and you probably
want a powered USB hub if you want more than kb/mouse.
A

RaspberryPi Tips (cont)
• Get a Pi Cobbler breakout board to make your life easier
• Cirago wifi/bluetooth dongle for $11, works great
• Buy a nice case (or 3d print one :D :D :D)
• Use a class 10 SD card if you can. dd is *slooooow* on a bad
card.
• There’s a camera module for $25.
A
explain pi cobbler is the ribbon cable attached to the one going around, it makes breadboarding easier
cirago wiﬁ/bluetooth seems to work great for basic IO and is low powered
cases keep you from shorting it out, i put some heatsinks so i can overclock mine a bit
class 10 sd cards are great, makes dd faster, and UX faster

GPIO Examples
using pi_piper gem, see: https://github.com/jwhitehorn/pi_piper
Event driven Raspberry Pi GPIO programming in Ruby
J

Output
J

Control schemes
• Serial Ports
• Connection Types
• Bluetooth
• USB
• GPIO
• Or my favorite, straight DRb over the network
A
lots of ways to control hardware, serial ports you ust write too like appending to a text ﬁle, can attach over bluetooth usb or gpio
(J interupts)
DRB

Part the second
Building something neat
J

Rubotnik
(This slide intentionally
left dumb)
J

So you have a RasPi
• We made it blink earlier with `pi_piper`
• What’s the next quick win we can get?
• (note: most of the upcoming code is super quick-n-dirty)
• Our goal is just to demystify this stuff - none of this code is
beyond a Ruby Nuby.
A
So we got some easy wins with the toys earlier, and we took a microcontroller and made an LED blink
What is our next steps?
Going forward we have a lot of quick code, goal isn’t to provide code examples but to demystify how this works. No magic here.

Twitter-powered blinkenlights
J

That was cool. Now what?
• How’s about some more direct control?
• Android -> JRuby <- DRb -> MRI -> RasPi -> Blinkenlight
A
So all this is cool, but how can we get into some more direct control of robots?
talk through adding android and DRB
J
Something about how awful writing custom protocols is
compared to DRb

J
This is the pickaxe example of DRb objects basically, completely standard...talk through class brieﬂy

So now android?
• Eww, java
• Not the worst thing in the world
• Tiny code
J
You came to this conference looking for Java code and we know it.

J
This interface is literally just a button

J
I don’t think this is scary Java code, but it has lots of things I learned about jruby that will be helpful

Use JRuby jars from ruboto project
J

...or JRuby asplode
J

if you don’t add stdlib to loadpath
you spend three days crying
J

AsyncTask because no network
on main thread (also, you need
the INTERNET permission for DRb)
J

Cat’ing ruby strings together.
With globals for control flow.
Nothing unusual here.
Move along.
J

RGB LED
A
What’s the next obvious step past a single red led?
A single RGB LED. Let’s make it happen

RGB LED
• So now we have an LED, so what’s the next simplest way to
ratchet up?
A

RGB LED
ratchet up?
• RGB LED, controlled by a color picker on the android device,
that changes color in realtime.
A

RGB LED
ratchet up?
• RGB LED, controlled by a color picker on the android device,
that changes color in realtime.
• Problem: RGB LED requires analog levels, but we only have
digital with pi_piper.
A

Pulse Width Modulation
A
So you can use PWM to simulate analog levels, but you’re really just switching them on and off. If an output is switched on 10% of
the time, evenly distributed, then it makes an LED look like it’s been sent a 10% max output signal.
Later we’ll use them for logic level stuff, but for now we’ll just treat PWM like fake-analog.

• RasPi only has one hardware PWM pin, and it’s shared with
the audio output (so you can’t use PWM and play sound at the
same time)
• So you can run pi-blaster to get 8 PWM outputs. It’s a
userland driver that hooks into the true PWM pin’s interrupt
and uses it to drive any GPIO pin like it’s PWM
• https://github.com/sarfata/pi-blaster/
J
pi-blaster, up to 8 PWM

• To completely turn off pin1:
echo "1=0" > /dev/pi-blaster
• To completely turn on pin1:
echo "1=1" > /dev/pi-blaster
• To set pin1 to a PWM of 20%
echo "1=0.2" > /dev/pi-blaster
A
Here’s how you use pi-blaster - everything’s just a ﬁle, and you write commands to it

J
Here’s a really basic class representing our rgb led. I’m just showing the red channel code here.

This class is actually
like 200 lines long :-
J
If we’d used any metaprogramming at all here, it’d have been much smaller. I promised quick-n-dirty code right?

Buuuuut
• Turns out that most RGB LEDs expect the common leg to be
high, and the channel-specific legs to be a modulated ground
(our code assumed the common leg would be ground)
• Luckily, Ruby’s awesome so when I ran into this when testing
it took all of three seconds to fix it up. NOTE: I also had to
run the 3.3V line to the common leg, then you’re just
modulating the difference (so 100% duty cycle for a given leg
means no voltage potential difference, or ‘off’)
J

ZOMG
J
Hey hey, object oriented programming is awesome.
Anyway, let’s go ahead and see what the android interface for this project looks like

A
Just a basic color picker, nothing fancy here. As you change the slider, we want the led updating in real time

J
More java code. Last time we ran code each time you hit a button, but now we have a slider. At ﬁrst I ran code on each change
event from the slider, but it turns out DRb can’t handle 200 messages/second and it would get laggy.

Timer Task that fires 20 times
per second. That seems to be
a sweet spot.
J
So my solution to this is to sample the UI 20x/second and send a message over DRb each time

If you’re going this route, have a single
method that accepts the state of the
User Interface. Then handle it on
the server side (rather than multiple
messages, one per user interface
component)
J
I found out later that apparently that’s what RC Controllers in the real world do anyway, so that was serendipitous. So there’s
basically all the code, how well does it work?

J
Pretty darn well....

So what’s next?
• Let’s finish this project up with something
fun.
• You go to the thrift store, and you buy one
of these bad boys for $2. This is the way
to go for this stuff by the way - there’s a
TON of old toys waiting to be awesome
again.
• Tank steering R/C base - this is the RAD2.
A
Alright, so we’ve got PWM control of a ruby process from android now. What next?
Let’s ﬁnish up by building an RC Tank steering thingie...
bullet points...

Speed Construction
• Take a Sabertooth 2x12RC ($65)
• Add a RasPi
• Add a 12V battery
• Add a cirago wifi/bt stick
• Mutilate a usb micro cable
J
Put all this stuff together aaaand

J
This is what you end up with

PWM and the Sabertooth
• So to control the Sabertooth,
you send a PWM signal per-
motor.
• 2000us pulse width: 100%
forward
• 1500us pulse width: idle
• 1000us pulse width: 100%
reverse
Mapped
to 0..1
values for
pi-blaster
J
Explain sabertooth logic levels, and show how we’re mapping them to pi-blaster levels

-1.0
1.0
A
Here’s the interface. Just two sliders, mapped from -1 to 1. Your standard tank steering controls

Map those values from the last
slide into our pwm output values
for pi-blaster
J

This all looks
familiar by now
J

This is
familiar
too
J

Demo
Advance to the next slide if the demo fails...

Thank you for coming
J
Thanks for being so attentive. As a rather generous thanks for attending our talk, we’ve provided free iPads under everyone’s
seats.
OMG THAT GUY ACTUALLY LOOKED of course we didn’t do that
A
Once again, thanks for coming. Any questions?

J
Thanks for being so attentive. As a rather generous thanks for attending our talk, we’ve provided free iPads under everyone’s
seats.
OMG THAT GUY ACTUALLY LOOKED of course we didn’t do that

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