#What is this

...For sheep are stupid, and have to be driven. But goats are intelligent, and need to be led.

-- Terry Pratchett

ROS is basically a distributed actor system. This code is just me playing with making something like that in Rust Erlang. Though ROS is a library, a set of tools, all sorts of stuff, and right now I'm just messing with a program.

Goals:

• Able to fly a drone around in some kind of simulation (Gazebo?)
• Integrate C/C++/Rust numerical code as necessary for heavy lifting
• Supervisor/monitor structure to automatically restart things that fail
• Fuzzing that injects failures, crashes nodes, etc.
• Sequencing and dependencies for startup
• Ability to easily record and replay message logs, with timing information
• Basic TF tree

Non-goals:

• Distributed operation on multiple systems at the same time
• GCS running the erlang shell or such as part of the same cluster
• General purpose tool for robotics
• Hard real time - it will give commands to a flight controller in soft real time, but the flight controller does the flying

Maybe goals:

• Run on an embedded-ish system a la nerves-project.org
• Actually fly a drone around

Possible alternatives:

• Rust + Bastion crate
• Alternative name: brobot

#Building & running

Use rebar3: https://rebar3.org/

Install deps:

sudo apt-get install libopenblas-dev liblapacke-dev

Building:

• rebar3 compile

Starting and running repl:

• rebar3 shell

Repl reference:

• https://www.erlang.org/doc/man/shell.html

Running tests:

• rebar3 eunit

Buiding docs:

• rebar3 edoc

Running lints:

• rebar3 dialyzer

#Tools

• Build tool: https://github.com/erlang/rebar3 and https://rebar3.org/docs/
• Unit tests: etest
• Linting: dialyzer
• https://github.com/rusterlium/rustler -- Rust NIF's
• Logging: https://hex.pm/packages/lager or https://hex.pm/packages/hut or https://hex.pm/packages/slogger

#References

• https://learnyousomeerlang.com/
• https://erlang-in-anger.com/

#Random notes

Things to figure out:

• Records
• Other changes since like 2009 when learnyousomeerlang was written
• Figure out build system
• Data structures: map, array(?), digraph, queue
• https://learnyousomeerlang.com/the-hitchhikers-guide-to-concurrency
• Might need a good matrix math library, can't find one for Erlang, there's some for Elixir but they aren't native code. https://github.com/elixir-nx/nx perhaps?
• Links: "If X dies then I die too". Monitors: "If X or Y or Z dies then I need to react to it".

One big question is what vehicle/flight controller to use. I can try to use a DJI SDK that I have some kind of access too... but DJI is increasingly in the doghouse and that doesn't seem to be changing, so, the only practical alternative seems to be PX4. I guess I should start learning how PX4 works.