Robotics with Elixir

Transcription

1 Meetup organized by Jean-François Cloutier Held at Big Room Studios, Portland, ME, USA Robotics with Elixir Part 1 Ghost in the Machine September 15, 2015

2 Lego Mindstorms The Greatest Toy Ever! And it got a whole lot better EV3 brick 1998 RCX 2006 NXT EV3 Faster CPU, more memory Linux! Bootable microsd card USB port Daisy chain up to 4 bricks Plug WiFi dongle

3 The programmable brick 4 sensor input ports 4 motor output ports Sensors and actuators 2 large motors 1 medium motor 1 color sensor 1 IR proximity sensor (with remote control) 1 touch sensor The goodies

4 And a whole bunch of Connectors Wheels, cogs, threads Etc. The goodies

5 Programming the EV3 The EV3 set comes with a customized version of LabView Visual programming? Snazzy! If you don't mind coding everything as one big sense and respond loop

6 OK it's not that bad but... We can do better. Blerch!

7 ev3dev.org to the rescue An updated LEGO Linux kernel (Debian) Bootable from a microsd card Can run most Debian packages apt-get install EV3 software rebuilt from the ground up Motor and sensor drivers use sysfs Exposed as character files Sensing = reading files Controlling = writing to files EV3 is now exposed to any and all programming languages running under Linux We can code the EV3 with Elixir!

8 Elixir and EV3 sitting in a tree Elixir/OTP = Functional Programming (FP) + Actor Model FP inputs function output No mutating state and no side-effects => simplicity and predictability OTP's Actor Model Linked processes communicating via self-contained messages Quarantined failures recovered through supervisor trees FP and (supervised) Actors are ideal for programming robots Or at least that's our working hypothesis

9 It's been done! Torben Hoffmann, CTO of Erlang Solutions, did it first So we'll do things a bit differently

10 But first, ev3dev and sysfs We'll be working with the tacho-motor and lego-sensor classes

11 sysfs: tacho-motor

12 tacho-motor commands Run commands Stop modes run-forever coast run-to-abs-pos brake run-to-rel-pos hold run-direct stop reset See doc at

13 tacho-motor specs, controls and state Specs (ro) driver_name count_per_rot commands stop_commands port_name Controls (rw) State (ro) duty_cycle_sp duty_cycle polarity position position_sp speed_sp speed speed_regulation state time_sp running ramping, stop_command holding, ramp_up_sp stalled ramp_down_sp command See doc at

14 Interacting with tacho-motors Large motor ssh cd /sys/class/tacho motor cd motor0 cat driver_name echo 50 > duty_cycle_sp echo run-forever > command echo stop > command Medium motor

15 sysfs: lego-sensor

16 Specs (ro) driver_name port_name modes num_values units lego-sensor specs, controls and values Controls (rw) mode See doc at State (ro) value<n>

17 Touch sensor Interacting with sensors Infrared sensor and remote control cd /sys/class/lego sensor cd sensor1 cat driver_name cat value0 cat modes echo IR SEEK > mode cat value0 cat value1 Color sensor

18 And Elixir in all this? Part 1 (this meetup) - Wrap ev3dev with immutable data and functions Hide the state mutations performed by sysfs (files act as global variables) Expose motors and sensors as static data Use functions to consume and produce (immutable) motors and sensors Part 2 (next meetup) - Use OTP to implement concurrent sense and control for autonomous robots Allocate a process to each sensor and motor to avoid race conditions, prevent damaging command sequences, detect state changes and emits events A central controller listens to events and drives a state machine that sends commands to motors Part 3 (and beyond) - Go nuts Complex event processing ( I am lost, I am stuck etc.)? Use a society of mind model (à la Pixar's Inside Out) instead of a central controller?

19 Modeling motors and sensors We can model the changing state of motors and sensors As mutable global variables is one way to model it (the non-fp way) Or as functions consuming and producing immutable data Device Get connected devices Alter controls Device Execute command (the FP way) Device Device Get state Device Device

20 Source code

21 Device data structure Devices - motors and sensors are represented as Elixir structs (think of them as records)

22 Device generation Functions that get the connected devices

23 Device initialization Function that gets device props from sysfs files (here, for motors)

24 Device control specs Function that gets the current motors specs

25 Controlling a device Functions that change control specs always return a new device

26 Getting device state Functions that access the device or sysfs read-only files containing device state

27 Getting device state

28 Synchronizing devices and sysfs Updating sysfs files to reflect current device specs

29 Interfacing with sysfs Reading from and writing to sysfs device files

30 Let's play with motors! iex> alias EV3.Tachomotor, as: TM... iex> [motor _] = TM.motors # Detect motors and hold on to the first one [%EV3.Device{class: :tacho_motor, path: "/sys/class/tacho motor/motor0", port: "outa", props: %{commands: ["run forever", "run to abs pos", "run to rel pos", "run timed", "run direct", "stop", "reset"], controls: %{duty_cycle: 0, polarity: :normal, position: 0, ramp_down: 0, ramp_up: 0, speed: 0, speed_mode: nil, speed_regulation: :off, time: 0}, count_per_rot: 360, stop_commands: ["coast", "brake", "hold"]}, type: :large}, %EV3.Device{class: :tacho_motor, path: "/sys/class/tacho motor/motor1", port: "outb", props: %{commands: ["run forever", "run to abs pos", "run to rel pos", "run timed", "run direct", "stop", "reset"], controls: %{duty_cycle: 0, polarity: :normal, position: 0, ramp_down: 0, ramp_up: 0, speed: 0, speed_mode: nil, speed_regulation: :off, time: 0}, count_per_rot: 360, stop_commands: ["coast", "brake", "hold"]}, type: :medium}]

31 Let's play with motors! iex> motor = TM.set_speed(motor, :rps, 1) # Set motor speed to 1 rotation per second... iex> TM.run motor # Stop the motor quickly... iex> motor = TM.reset # Reset the motor to its initial state... iex> motor = motor > TM.set_duty_cycle(50) > TM.reverse_polarity # 50% power and in reverse... iex> motor = TM.run_for(motor, 10000) # run for 10 secs... iex> IO.puts TM.current_speed(motor, :dps) # Print the current speed in degrees per sec 360 iex> TM.stalled? motor # Is the motor stalled? false

32 Let's play with sensors! iex> alias EV3.LegoSensor, as: LS... iex> sensors = LS.sensors # Detect all connected sensors [%EV3.Device{class: :sensor, path: "/sys/class/lego sensor/sensor0", port: "in3", props: %{mode: "TOUCH"}, type: :touch}, %EV3.Device{class: :sensor, path: "/sys/class/lego sensor/sensor1", port: "in1", props: %{mode: "IR REMOTE"}, type: :infrared}, %EV3.Device{class: :sensor, path: "/sys/class/lego sensor/sensor2", port: "in2", props: %{mode: "COL COLOR"}, type: :color}] iex> ir = sensors > Enum.find((LS.infrared? 1)) # Get an infrared sensor %EV3.Device{class: :sensor, path: "/sys/class/lego sensor/sensor1", port: "in1", props: %{mode: "IR REMOTE"}, type: :infrared} iex> color_sensor = sensors > Enum.find((LS.color? 1)) # Get a color sensor... iex> touch = sensors > Enum.find((LS.touch? 1)) # Get a touch sensor...

33 The infrared sensor iex> alias EV3.InfraredSensor, as: IR... iex> IR.proximity(ir) # Get proximity of obstacle as percent of range 62 iex> IR.seek_distance(ir, 1) # Get distance (as % of range) of beacon on channel 1 15 iex> IR.seek_heading(ir, 1) # Get heading of beacon on channel 1 (far left is 25) 12 iex> IR.remote_buttons(ir, 1) # What buttons were pushed on remote set to channel 1? %{blue: :down, red: :up}

34 The color sensor iex> alias EV3.ColorSensor, as: CS iex> color_sensor = CS.set_reflect_mode(color_sensor) reflected light detection mode # Set to %EV3.Device{class: :sensor, path: "/sys/class/lego sensor/sensor2", port: "in2", props: %{mode: "COL REFLECT"}, type: :color} iex> CS.reflected_light(color_sensor) # How much light is reflected from the sensor (in % of maximum)? 16 iex> CS.ambient_light(color_sensor) # How much ambient light is detected (in % of maximum)? 3 iex> :blue CS.color(color_sensor) # What color is detected?

35 The touch sensor iex> alias EV3.TouchSensor, as: TS... iex> TS.pressed? touch false iex> TS.released? touch true

36 I have a blog

37 Thank you! Next meetup Robotics with Elixir, part 2 Soul of a New Machine Programming autonomous robots with Elixir/OTP Processes, events, finite state machines, oh my!