Week One: Discord, Robot Arms, and Livebook Widgets

Beam Bots gets a Discord channel, a 5-DoF robot arm donation, interactive Livebook widgets, a safety system, and two servo drivers. Not bad for a week.

It's been six days since I announced Beam Bots, and things have moved faster than expected. Here's what happened.

We Have a Discord Channel

The Elixir Discord community has given Beam Bots its own #beam-bots channel. If you want to chat about resilient robotics on the BEAM, ask questions, or just lurk, come say hello.

Frank Hunleth Donated a Robot Arm

Frank Hunleth, co-creator of Nerves, has donated a Trossen Robotics WidowX-200 5-DoF robot arm to the project.

WidowX-200 Robot Arm

This is a proper piece of kit - Dynamixel servos, aluminium construction, and enough reach to knock things off my desk.

This means I'll be able to test Beam Bots against real hardware that isn't just a servo taped to a breadboard. Expect tutorials and examples using this arm as the development progresses.

Thanks Frank.

BB Kino: Livebook Widgets for Robot Control

The biggest code drop this week is bb_kino - a suite of interactive Livebook widgets for controlling and monitoring BB robots.

BB Kino Demo

The package includes:

Safety Widget - arm/disarm controls with real-time state indicators
Joint Control Widget - sliders for setting joint positions, respecting limits
Event Stream Widget - live message monitoring with path filtering
Command Widget - dynamic forms for executing robot commands
3D Visualisation Widget - interactive Three.js rendering with real-time joint updates
Manage Robot Smart Cell - a unified dashboard combining everything

This isn't the "LiveView-based introspection" from the roadmap - that's still planned as an embeddable dashboard for Phoenix apps. But for prototyping and development, being able to control your robot interactively in Livebook while watching state update in real-time is pretty useful.

Safety System

BB v0.4.0 adds BB.Safety, a centralised arm/disarm controller that ensures your robot can always be stopped safely. Key features:

BB.Safety behaviour - actuators controlling hardware implement a disarm/1 callback
Global safety state - one place to arm or disarm all safety-registered components
Error state handling - if disarm callbacks fail, the robot enters an :error state and won't re-arm until you explicitly acknowledge with force_disarm/1
Documentation covering BEAM's soft real-time limitations and why you still need a hardware kill switch

The safety system is critical infrastructure. When things go wrong, you need the disarm to work even if the process that controlled the actuator has crashed. The disarm/1 callback is designed to work without GenServer state for exactly this reason.

Servo Driver Packages

Two new packages for driving RC servos:

bb_servo_pigpio - drives servos via GPIO PWM on Raspberry Pi using pigpio. Good for simple setups with a few servos directly connected to GPIO pins.

bb_servo_pca9685 - drives servos via the PCA9685 16-channel PWM controller over I2C. Better for projects needing more channels or cleaner wiring.

Both packages implement BB.Safety for safe disarm, use the standard actuator command interface, and work with BB.Sensor.OpenLoopPositionEstimator for position feedback on servos without encoders.

Other Changes

Standard actuator command interface - BB.Actuator.set_position/4 and friends provide a consistent API across all actuator types
OpenLoopPositionEstimator - estimates joint position over time based on commanded velocity, for servos that don't report their actual position
BeginMotion/EndMotion messages - actuators now publish motion lifecycle events for coordination and logging

What's Next

The WidowX-200 uses Dynamixel servos with their own protocol, so I'll be writing a Dynamixel driver package. After that, I want to get inverse kinematics working so I can command the arm to move to a point in space rather than specifying individual joint angles.

The rover project is on hold until the arm is working. One robot at a time.