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Beam Bots - The framework for resilient robotics.

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usage-rules.md 

<!--

SPDX-FileCopyrightText: 2026 James Harton



SPDX-License-Identifier: Apache-2.0

-->



# Beam Bots (BB) Usage Rules



BB is a framework for building resilient robots in Elixir. You describe a

robot's physical structure with a Spark DSL (`use BB`); BB compiles that to a

struct and generates a supervision tree that mirrors the robot, so a crash is

isolated to the affected subtree rather than taking the whole robot down.



Read the documentation before reaching for a feature. Do not assume prior

knowledge of BB — its DSL, its safety model, and its message conventions are

specific and easy to guess wrong. Search it with

`mix usage_rules.search_docs "<topic>" -p bb` and consult

[hexdocs](https://hexdocs.pm/bb) rather than inventing an API.



## Golden rules



1. **A robot is a module that does `use BB`.** By convention it is named

   `MyRobot.Robot`. Never hand-roll GenServers or a `Supervisor` for a robot's

   components — declare them in the DSL and let BB build the tree.

2. **Physical quantities use the `~u` sigil, never bare numbers:**

   `~u(90 degree)`, not `1.57`. `use BB` brings the sigil into scope. Values are

   converted to SI base units (metres, radians, kg) in the compiled struct.

3. **A robot starts `:disarmed` and ignores motion commands until armed.**

   Arming runs user-defined prearm checks. Change the safety state through the

   command system, never by calling `BB.Safety` directly.

4. **Talk to a running robot through its public API** — `BB.PubSub`,

   `BB.Actuator`, `BB.Parameter`, `BB.Motion`, and the command functions

   generated onto the robot module — not by messaging its processes yourself.



## Sub-rules



Consult the focused rules for the area you are working in:



| Sub-rule | Covers |

|---|---|

| `bb:dsl-topology` | Defining a robot: links, joints, units, attaching components |

| `bb:safety-and-commands` | The arm/disarm contract, the state machine, writing commands |

| `bb:pubsub-and-sensors` | Subscribing to and publishing messages; message naming |

| `bb:actuators` | Commanding motion; joint-space vs motor-space |

| `bb:kinematics` | Forward kinematics and inverse kinematics |

| `bb:parameters` | Runtime-adjustable configuration and bridges |

| `bb:simulation` | Running a robot without hardware |

| `bb:anti-patterns` | The mistakes assistants make most often |



Pull them into your project with `mix usage_rules.sync <file> bb:all`.



## Further reading



- [Your First Robot](https://hexdocs.pm/bb/01-first-robot.html) — start here

- [DSL reference](https://hexdocs.pm/bb/dsl-bb.html)

- [Understanding Safety](https://hexdocs.pm/bb/understanding-safety.html)